Temporary Queries
Using theTmpQuery Class in Reports and Forms
by Michael Nuwer



dBASE Plus has a number of powerful and easy-to-use tools for modeling data. With a dataModule you can define relationships among query objects, create calculated fields, add lookup rowsets and much more. When such a dataModule is added to a form object, the User Interface controls have instant access to all the data.

Connecting to data from a report is not quit as easy. The dBASE Report Designer works well with a single query object or with two queries that hold a parent-child relationship. However, it has difficulty with parent-child-grandchild relationships and with queries where the parent has two or more children.

There are different strategies used to deal with these limitations. Some developers use Vic McClung’s Printer Class while others use Crystal Reports. Those how wish to use the dBASE Report Designer have found that using a temporary table is sometimes helpful. With this latter method the data to be printed is added to a temporary table based on the needs of the report and the selection criteria of the user. The report is then printed from this temporary table.

This article explores a custom query class designed specifically for creating and using temporary tables. Todd Kreuter is the author of this class, which can be found in the file named TmpQuery.cc.

Files refered to in this article 

The dBASE Query Class

Query objects are the center of the dBASE data model. They are used to reference fields in an individual table, or a subset of fields from a table or fields from multiple tables joined by an sql statement. When a query is added to a form, a dataModule or a report, the Form Designer streams code similar to the following:
this.MYTABLE1 = new QUERY()
this.MYTABLE1.parent = this
with (this.MYTABLE1)
   left = 48
   top = 13
   database = form.database1
   sql = "select * from MyTable.dbf"
   active = true

This code creates an instance of the query object and then assigns a few properties. When the active property is set true, the statement stored in the sql property is executed and dBASE creates a rowset.

There are two events that fire when a query object’s active property is set true. First the canOpen() event fires. This event determines whether the query can be opened (or activated). The event handler assigned to this property must return a true or false to indicate whether the object is opened. The canOpen() event is also used to do something with the query, just before it opens. In this case, the canOpen() event handler would always return true. The TmpQuery class exploits this property of the query class.

The second event that fires when a query object’s active property is set true is the onOpen() event. This event fires after the query is opened successfully. A return value is not required when an event handler is assigned. The onOpen()event is used to do something with the query, the rowset, or the fields array immediately after it is active. For example, the onOpen() event handler is often used to create a calculated field and add it to the rowset.

The TmpQuery Class

Todd Kreuter’s TmpQuery class is subclassed from the dBASE Query class. It thereby contains all the properties, methods, and events of that build-in class. In addition, Todd has added functionality to the class. The new class contains custom properties and methods designed to work with temporary tables. For example, this class contains a method to create a table, another to create an index, and another method to delete the table when the query is deactivated.

One advantage of this class is that a temporary table is created from code only when it is needed and deleted after it has been used. This feature reduces clutter. In addition, the temporary table is created on the user’s local hard drive, which is convenient in a multiple users system. If two users run the same report at the same time, each will have their own customized temporary table. In fact, a single user can run two instances of the same report and each will have it’s own temporary table.

The following HTML table contains a complete list of the custom properties and methods found in the TmpQuery class. It is taken from the header of TmpQuery.cc. Some of these properties and methods are intended for use by the programmer while others are for internal use. Nevertheless, a complete list is useful in order to understand how the TmpQuery class works.
Properties Comments
  skeleton Skeleton for table name, i.e. "_TMP????"
  userDefPath Allow user to specify table path. Uses getDirectory() prompt This overrides useTempPath setting.
  useTempPath Determine if table is created in the OS temporary directory, default is true. Set to false to create in current directory.
  dropOnClose Delete table when query closed. Works only when setting query.active = false. This is disabled when closed internally.
  CreateTable() Creates Table from fields array.
  CreateIndex(tagName, tagExpression) Create an index tag. Returns success on creating index tag (Logical). 
tagName - Index Name 
tagExpression - Index Expression
  CreateFromQuery(qSource, bIndex) Creates Table from existing Query 
qSource - Source query 
bIndex - Whether to create indexes used in Source.
  PackTable() Pack the table. Returns success on packing table (Logical).
  EmptyTable() Empty the table. Returns success on emptying table (Logical).
  DropTable() Deletes the file. Returns success on dropping table (Logical).
  Internal Properties  
  fullPath String containing full path necessary to locate the table, being the path + the tableName.
  fields Array containing fields list for createTable.
  Internal Methods  
  AddField(cField, bSQL) Adds element to fields array 
cField, field Definition 
bSQL, cField is in SQL Syntax (no conversion)
  setFullPath Sets path and file name of table, custom properties determine path and file name. Returns success on setting full path (Logical).
  setActive(bActive) For setting active property internally. Used to prevent canOpen and onClose events from firing 
bActive - Setting of query.active
  Internal Events  
  canOpen() Sets the sql for the query using the name of temp table. Call TMPQuery::CanOpen() when overridden.
  onClose() Drop table when query closed, when applicable. Only fires when set query.active to false.

Using TmpQuery.cc with Reports

The first two reporting examples discussed in this article are comprised of three elements. First, there is a dialog form in which a user selects some criteria. This form contains the TmpQuery object and creates a temporary table populated with data. The name of the temporary table and the name of the report to print are passed to the second element, which is the Preview form found in the dBASE User Function Library Project (dUFLP). The Preview form loads the third element, which is the report, into a reportViewer object and renders the data from the temporary table.

In the next few paragraphs we will discuss adding a TmpQuery object to a dialog form. To begin the TmpQuery class needs to be loaded into memory. Typing the following line in the Command Window does this:
set procedure to tmpquery.cc additive

Next a new form must be opened in the Form Designer. On the Custom tab of the Component Palette you should see an icon for the TmpQuery object. Drag this object onto the form. If you were creating a normal query object, you would set the sql property so the query could select data from the table and you would set the active property true. The TmpQuery object, however, is a bit different from the normal query object because there is no table that can be used in the sql property.

When using a TmpQuery object the table is created in the query’s canOpen() event handler. Thus you should use the Inspector and add a canOpen() event handler for the TmpQuery1 object on your form. (You will be prompted with a message that asks whether you want to override the existing event handler. Click yes to the question.)

The code generated for the resulting form will look very similar to the following:
class DemoForm of FORM
   set procedure to tmpquery.cc additive
   with (this)
      height = 16
      left = 75.8571
      top = 0.3182
      width = 40
      text = ""

   this.TMPQUERY1 = new TMPQUERY()
   this.TMPQUERY1.parent = this
   with (this.TMPQUERY1)
      canOpen = class::TMPQUERY1_CANOPEN
      left = 2
      top = 0.5
      width = 0
      height = 0

   function tmpquery1_canOpen
      return true



The TmpQuery object should not reference a database object. The createTable() method in the TmpQuery class will ignore the database property if it is set. A database object can be used with other query objects, the ones that are selecting data from your permanent tables. But the temporary table is stored in the application’s working folder or in the Windows temp folder. It is not stored in a database folder.

The canOpen() event handler is an important part of the TmpQuery class. This is where the fields are defined and the table is created. It is also where the sql property is set to point to the temporary table. This last step can be done manually or by calling the canOpen() event handler in the super class (the one you overrode above).

The following canOpen() event handler is taken from one of the sample forms (ItemMover.wfm) used in this article.
Function TMPQUERY1_canOpen
   with (this.fields)
      add("Last Name C20")
      add("First Name C20")
      add("Street1 C40")
      add("City C30")
   this.useTempPath = false
   this.dropOnClose = false
   return TMPQuery::canOpen()

The fields array (this.fields) is one of the internal properties of the TmpQuery class. The developer adds fields to this array and the class adds them to the temporary table. I have found it most useful to use field names that match the field names in the corresponding permanent table. As we will see later, field name matching simplifies the task of moving data between tables. Notice that this array is a property of the query object, it shouldn’t be confused with the fields array contained in a rowset. The syntax for adding a field to the TmpQuery’s fields[] array is discussed below.

After fields are added to the fields[] array there are two custom properties, useTempPath and dropOnClose, which are set false. I set these to false while developing and debugging my code. I will then change these properties to true after all is working the way I want. The first custom property tells the TmpQuery class to create the temporary table in the current folder, rather than in the user’s Windows temp folder. While developing code, temporary tables are easier to find when they are in the current folder. The second property tells the TmpQuery class not to delete the temporary table when the query is deactivated. This too is useful while developing a form, because one can see what gets into (or doesn’t get into) the table.

The last line in the above code must return a call to the canOpen() method contained in the super class. So you must be sure to replace return true with return TMPQuery::canOpen(). This is very important, because that method sets the sql property.

  If you need or want to set the sql property manually, this can be done by accessing the temporary table name with the fullPath property. In this case the canOpen() event handler should not return a call to the super class. Instead, the following lines should be used.
return TMPQuery::canOpen()
this.sql = [Select * from '] + this.fullPath + [']
return true



The TmpQuery class lets you add fields using a shorthand syntax or standard SQL syntax. The field definition is a string with the field name and the data type. Field names are separated from their data type with a space, no other delimiter is needed. Spaces in field names are permitted. If you use standard SQL syntax the second parameter in the add method must be true. The following table itemizes the short hand and standard SQL syntax for each data type.

Data Type Short Hand Standard SQL
  Character(n) Cn Char(n)
  Numeric Nx,y Numeric(x,y)
  Date D Date
  Logical B Boolean
  Autoincrement A AutoInc
  TimeStamp T TimeStamp
  Long Integer L Integer
  Small Integer S SmallInt
  Float Fx,y Float(x,y)
  Binary On,t BLOB(n,t)

  When you have a large number of fields that need to be created in a temporary table, you may want to use the Command Window to display the field names and data types from the permanent table, and then edit the list. You can do this by typing the following in the Command Window. Then copy the text in the result pane and paste it into the Source Code Editor.
use theTable
display structure

Another technique is to stream the output directly to a text file using the following commands, and then open that text file in an editor:
set alternate to "FieldList.txt"
set alternate on
use theTable
display structure
close alternate
set alternate off


Form One Example (ItemMover)

The sample files that accompany this article include a form named ItemMover.wfm. This form contains a TmpQuery object that is identical to the one above. In addition this form inherits a set of controls from a custom form. I designed the sample this way so that the controls that are not a part of using TmpQuery are isolated in the custom form. This way I hope we can focus on the elements in the ItemMover.wfm and not get distracted (or confused) by the other elements.

The general idea for this form is that a user will use the ItemMover control to choose customer names that they wish to print. When the Print pushbutton is pressed, the onClick() event handler finds the selected customers in the Customer1 rowset and adds their data to the TmpQuery1 rowset. I have tried to keep this first example as simple as possible. Therefore the data to be printed is drawn from only one table and only four fields are used.

When the ItemMover listbox is populated with customer names, the corresponding key field value (Customer ID in this case) is added to the right of the string. The pseudo-code looks like this:
Name + space(20) + ID

With this technique the customer ID is not visible to the user, but it is available in listbox’s datasource for later use.

The Print button’s onClick() event handler is responsible for appending the correct data to the TmpQuery object. The code below is used in that event handler. It is divided into four parts so that we can discuss each piece. Part one is used if the form is going to print a second instance of the report. If the temporary table has already been populated with data, this code empties the table so that new data can be added.

The code in part two loops through the array that contains the selected customer names. In each iteration, the customer ID is taken from the right end of the array element and used to seek the matching value in the Customer1 query. Then the TmpQuery1 rowset is placed into append mode.

Part Three of the code is the inner loop. This cycles through the TmpQuery’s fields array. If the field name in the TmpQuery rowset matches the field name in the Customer1 rowset, then that value is added. This is a very convenient loop, especially when there are a large number of fields in the temporary table. With it we do not need to hard code each of the fieldnames. However, it works only when the field names in the permanent table are the same as the fieldnames in the temporary table.
Function PBPRINT_onClick
   // Part one
   if form.tmpQuery1.rowset.first()

   // Part two
   private cFieldName
   local aList, n, i, nID
   aList = form.ItemMover1.aList2
   for i = 1 to aList.size
      nId = val(right(aList[i],20))

      // Part Three
      for n = 1 to form.tmpquery1.rowset.fields.size
         cFieldName = form.tmpquery1.rowset.fields[n].fieldname
         if type("form.customer1.rowset.fields[cFieldName]")=="O"
            form.tmpquery1.rowset.fields[cFieldName].value = ;

   // Part four
   form.tmpquery1.createIndex("index1","Last Name")


Part four is one line, which creates an index tag in the temporary table. The first argument in this method is the tag name and the second argument is the index expression. In this example a generic index name is used. One reason to do this is that it’s easy to remember: all the reports that use a temporary table have the same index name. But perhaps more important, if your want to give your user the option to choose a sort order, you would do this by changing the index expression. However, the report object always looks for the generic tag name, which means that the controlling index is independent from the sort order of the data.

You might have noticed that the index is being created after the table is loaded with data. An alternative approach would be to create the index in the query’s canOpen() method immediately after the table is created. In that case the index will be updated with each row that is appended. By creating the index after the table is loaded with data, the index is updated only once. This approach can improve the application’s performance particularly when a large amount of data is being added to the temporary table.

  Normally a temporary table that is used in a report will have only one index. This means that the index often needs to be based on a compound expression. The createIndex() method is designed to create this type of index. The expression argument is a literal string and it is used internally to actually create the index. Consequently, the expression that you pass to the createIndex() method should be the same string as you would write in the Table Designer. All of the following are valid index expressions. They are formatted as literal strings for use in the createIndex() method.
"upper(LastName + FirstName)"
"left( upper( trim(:last name:)+', '+:first name: ) + space(40), 40)"



The only other element that needs to be added to our dialog form is a method to handle the form onClose() event. In this event handler the TmpQuery1’s active property needs to be set false. When this is done (and when the dropOnClose property is false), the TmpQuery class will delete the temporary table from the user’s hard drive.
Function form_onClose
   form.TmpQuery1.active = false

We now have a form that will create a temporary table and populated it with user selected data. We still need to pass this data to the report object that will print it, but before considering this feature lets look at another form, which also creates a temporary table.

Form Two Example (GetDates)

The second example form presented in this article offers a bit more complexity than the earlier example. Like the ItemMover form, this form creates a temporary table and populates it with data that matches a user selected criteria. In this case the use selects a date range and a sort order for the report. The table that is created by this dialog form is sometimes called a “flat file” because it contains data from two tables that hold a parent-child relationship. This means that when a parent record has more than one child, the parent data will be duplicated in the temporary table.

The form’s user interface is a simple get dates dialog. It’s purpose is to get the date range from the user and print a report filtered for that range. Additionally, the user can choose a field to sort the output.

Although this form is similar to the ItemMover form it is coded a bit different. My objective is to show some of the variation that is possible with the TmpQuery class. In this form, the TmpQuery object is created in the Print pushbutton’s onClick() event handler and the temporary table is populated in the TmpQuery’s onOpen() event handler.

The code below executes when the Print button is clicked. The temp table is created here rather than in the form’s Constructor code.
Function PBPRINT_onClick
   // Part One
   set procedure to tmpquery.cc additive
   if type("form.qTmp") == "O"
      form.qTmp.active = false

   // Part Two
   form.qTmp = new tmpQuery()
   form.qTmp.parent = form
   with (form.qTmp)
      canOpen := class::qTmp_canOpen
      onOpen  := class::qTmp_onOpen
      active  := true

   // Part Three
   // Before the index can be created the query must be
   // deactivated. After the index exists the query
   // set active again. This means that the onOpen
   // event fires as second time. The next line
   // prevents the event from firing a second time.
   form.qTmp.onOpen = null
   if form.rbLastName.value
      form.qTmp.createIndex("Index1","Last Name")
      form.qTmp.createIndex("Index1","City + :Last Name:")


Part one in this code tests whether the form already contains a TmpQuery object and, if it does, sets the active property false. The temporary table will thereby be deleted. This is necessary because the form is designed to let the user create multiple reports without closing the dialog form.

The second part of the event handler creates an instance of the TmpQuery object and assigns methods to the canOpen() and the onOpen() events. When the active property is set true, these events fire and the methods are called.

The qTmp_canOpen() method is substantially the same as the canOpen() method in our first example. It defines the fields and creates the table.
Function qTmp_canOpen
   with (this.fields)
      //  Fields in parent table
      add("Last Name C20")
      add("First Name C20")
      add("City C30")
      //  Fields in Child table
      add("Invoice ID S")
      add("Order Date D")
      add("Pay Type C3")
   this.useTempPath = false
   this.dropOnClose = false
   return TMPQuery::canOpen()

The actual query is executed after this code runs and then the onOpen() event fires. For the current example, we put the code to populate the temporary table in the onOpen() event handler.
Function qTmp_onOpen
   local dStatDate,dStopDate,oForm
   dStartDate = oForm.spinboxStart.value
   dStopDate = oForm.spinboxStop.value
   oForm = this.parent
   until not oForm.invoice1.rowset.next()

This code begins by filtering the child table from the user defined date range. The rowset’s setRange() method is used because the table is indexed on the invoice date, but you can alternatively use the filter property or the canGetRow() event or you can loop through the entire table and skip rows that don’t meet the condition.

When I create a flat file from a parent child relationship, I always loop throw the child table. When a record is found that meets the condition, an appendRow() method is called. This method actually appends the row to the temporary table. In the current example every row is added to the temporary table because the filter restricts the data. However, this is not always the case. I have loops that contain some elaborate case statements for selecting data.

The appendRow() method begins by appending, into the temporary table, data from the child table. It then seeks the parent record in the master table and adds those fields to the temporary table. Field matching is again used to simplify the coding.
Function appendRow
   local rTemp,fTemp,i,cLookFor,rParent,fParent
   private fChild ,cFieldName

   fChild = form.Invoice1.rowset.fields
   fParent = form.Customer1.rowset.fields
   rParent = form.Customer1.rowset
   fTemp = form.qTmp.rowset.fields
   rTemp = form.qTmp.rowset

   for i = 1 to rTemp.fields.size
      cFieldName = fTemp[i].fieldname
      if type("fChild[cFieldName]")=="O"
         fTemp[cFieldName].value = ;

   //  Lookup Parent Record
   cLookFor = fChild['Customer ID'].value
   if rParent.findKey( cLookFor )
      fTemp['Last Name'].value = fParent['Last Name'].value
      fTemp['First Name'].value = fParent['First Name'].value
      fTemp['City'].value = fParent['City'].value


The final part of the code in the Print button’s onClick() event handler creates an index based on the user selected sort order. This is a bit more complicated than it appears. The query must be deactivated (and the table closed) to create the index. The TmpQuery class handles this task, and then, after the index is created, it reactivates the query object. When this happens the canOpen() and onOpen() event fire, which can cause all kinds of problems. A second temporary table can be created and the data can be added a second time.

To avoid these problems, the TmpQuery class breaks the link between the canOpen() event and its event handler before creating the index. The class does not, however, break the link between the onOpen() event and its event handler. This is why we set the onOpen property null in the code. Other table operations that require exclusive use must be handled the same way. These include the EmptyTable() and PackTable() methods.

Before turning our attention to the report, we need to add an onClose() method to the form. This method needs to deactivate the TmpQuery object so that the temporary table is deleted.
Function form_onClose
   if type("form.qTmp") == "O"
      form.qTmp.active = false

That’s about it. Creating a temporary table with the TmpQuery class is really quit easy.

At this point in our discussion the ItemMover and GetDates forms have created a temporary table and populated it with the data that will be used in the report. The next part of the discussion focuses on creating the report and linking the report to the form.

Before turning to the report, this would be a good time to clean up some of the undeleted temporary tables. Be sure all the dialog forms are closed and use Windows explorer (or the dBASE Navigator) to delete all of the temporary tables. The file names will begin with _tmp (unless you modified the skeleton property). These files should be in the current folder (the folder in the dBASE Navigator’s “Look in” field) if the useTempPath is false and if the TmpQuery object does not have a database property.

Create the Reports

Creating a report based on a temporary table is problematic to say the least. After all, the table doesn’t exist until the dialog form opens and it is deleted when the form closes. The way I deal with this issue is to make a working table that I can use for designing or modifying the report. There is no substantial difference in the procedure used to create the ItemMover report or the GetDates reports so for expository purpose I will discuss creating the report used with the GetDates form.

Run the GetDates form, enter a date range, and click the Print button. This will create a temporary table and an index file. Without closing the form, use the Command Window to make of a copy of this file. The following commands, adjusted for the name of the temporary file, will create that copy. (Use the Navigator to find the actual file name. There should be only one temporary file if you deleted all the temporary table before running this form.)
use _tmp7990
copy to tmpGetDates with production

Now tmpGetDates.dbf can be used to layout the report, which can be done just like you would if you were using a permanent table. After the report is designed to your satisfaction, there are two methods that need to be added. The first method is an overridden render() event and the second is a query canOpen() event.
Function form_render
   return GETDATESREPORT::render()

Function tmpgetdates1_canOpen
   return true


We are designing this reporting system so that the report is rendered with the dUFLP’s Preview form. (In the next section we will design a system that uses it’s own previewer.) When using this form the standard technique for passing parameters to a report is to use it’s render() event. The basic idea is that our dialog form will create an array that contains the parameters to be passed to the report. This array is assigned as a property of the Preview form and that form passes it along to the report. The report needs to check for this array and use the values it contains. When using the dUFLP’s Preview form, that check is done when the report is rendered. The following is the example from the header of the Preview form.
// this is an overridden render event -- the idea
// being that in order to use a params array
// for a report, we need to check to see if it
// exists ... either here or in a reportViewer
// (i.e., PREVIEW.WFM)
// The 'runonce' property checks to make sure
// that the render event code based on the params
// array is only called once -- when the report is
// first loaded ... reportViewers call this when
// rendering each page, which could cause problems,
// depending on your code.
if type( "this.runOnce" ) # "L"
   this.runOnce = true
   if type( "this.reportViewer" ) == "O"
      // we are being called from a reportViewer
      // check to see if the reportViewer's form has
      // a params array:
      if type( "this.reportViewer.form.params" ) == "O"
         // set params array:
         this.params = this.reportViewer.form.params
   // if we have a params array, we need to set the
   // filter for the report:
   if type( "this.params" ) == "O" and ;
      this.params.isKey( "Filter" )
      // assign the filter property of the
      // rowset being used for the report:
      this.address1.rowset.filter := this.params[ "Filter" ]

endif  // this.runOnce

super::render()  // call the overridden render code don't
                 // forget this or report will never render!


For more detail on passing parameters to a report via the Preview form see Example of Preview.wfm and Report Parameters by Steve Hawkins.

  A slightly different approach to using the Preview form is to use a custom report and put the render() event in that class. However, instead of setting the filter or whatever, call a method named setParams(). In your report include a method named setParams() and set whatever parameters are specific to the given report.

For an example of this type of report, see the custom reports in the dUFLP. These files already contain the overridden render method and the call to a setParams() method. For some working examples of this approach see Reporting with dBASE Plus: Using Temporary Tables by Michael Nuwer 



In our example reports, a filter is not needed because the data has already been selected. Remember the report is using an existing table, albeit a temporary table, it is not creating its own TmpQuery. But we need to be sure that the report is using the temporary table, which can be a bit tricky because the file name is randomly generated. The problem is that the report’s query object opens a table when the report is instanced but before it is rendered (and therefore before the render() event fires). In other words the query is included in the report’s Constructor code.

The easiest way to handle this problem is to deactivate the query and then reactive it in the render() method. This should be done after the parameters[] array is assigned to the report so that when the query opens the second time, the canOpen() method can use the parameters.

The following is the render() event used in the GetDates report. I have stripped the comments and the added coded is indicated in bold print.
Function form_render
   if type( "this.runOnce" ) # "L"
      this.runOnce = true
      if type( "this.reportViewer" ) == "O"
         if type( "this.reportViewer.form.params" ) == "O"
            this.params = this.reportViewer.form.params
      if type( "this.params" ) == "O" and ;
          this.params.isKey( "temptable" )
          form.tmpGetDates1.active := false
          form.tmpGetDates1.active := true
          form.tmpGetDates1.rowset.indexName := "index1"
   return GETDATESREPORT::render()

When the query is activated a second time, the params[] array is attached to the report and the canOpen() event fires. The canOpen() event handler can now be used to determine which table to open. The code looks like the following:
Function tmpitemmover1_canOpen
   if type( "this.parent.params" ) == "O"
      this.sql = 'select * from "' + ;
      this.parent.params['temptable'] + '.dbf"'
      this.sql = 'select * from "TmpGetDates.dbf"'
   return true

The last thing that we need to do is to run the preview form and open the report. Return to the GetDates dialog form and locate the pbPrint_onClick() method. The code in that method creates a TmpQuery object and populates the tables with data. After those procedures are complete the Preview form must be opened. The following code is the standard way to call the Preview form.
aParams = new AssocArray()
aParams[ "temptable" ] = form.qTmp.fullPath
set procedure to preview.wfm additive
fPreview = new PreviewForm()
fPreview.bModal = true
// these next two commands must be in this sequence
fPreview.params = aParams
fPreview.viewer.fileName := "GetDates.rep"

The one point to note with respect to using temporary tables is that the table name must be passed to the Preview form in the parameter array. This is indicated above in bold type.

  The metamorphous of the parameter array: It might be worthwhile to take a brief detour and examine how the parameter array gets from the dialog form to the report.

In the Dialog form the parameters array is created and it is assigned as a property of the Preview form just before that form is opened.
aParams = new Array()
fPreview.params = aParams

In the Preview form a report is either displayed in a reportViewer object or it is sent to the printer. When the report is rendered in the reportViewer, the Preview form does nothing with the parameter array. However, when the report is rendered to a printer, the Preview form assigns the array as a property of the report object:
r.params = form.params

When the report is called from the reportViewer the render method assigns the parameter array as a property of the report object.
this.params = this.reportViewer.form.params

Now the parameter array can be accessed as a property of the report and the actual parameters can be used to configure the report according to whichever element has been passed.
this.params[ "theElement" ]

The following schematic highlights the path of the parameter array.


If all of the pieces are configured correctly the GetDates reporting system should work. Run the GetDates form, enter a date range and choose a sort order; then click the Print button. The preview form should open and the report should be displayed in the reportViewer object. Verify that the dates in the report are within the selected date range. One source of error in this system is that the report is using the tmpGetDates.dbf rather than the actual TmpQuery created table.

There is one last issue that we need to discuss before moving on to the next section. Before the foregoing report is deployed to a user’s machine, the query object needs to be deactivated in the Constructor code. Currently, the tmpGetDates table is opened when an instance of the report is created, then it is closed and the temporary table is opened when the render() method runs. The tmpGetDates table is needed only while designing the report and we don’t want to deploy it to all the client computers. The easiest way to deal with this is to set the query’s active property false. This way when the report is instanced, the query will not attempt to open tmpGetDates.

If you open the report in the Source Code Editor the query object will look similar to the following.
this.TMPGETDATES1.parent = this
   with (this.TMPGETDATES1)
      canOpen = class::TMPGETDATES1_CANOPEN
      left = 810
      top = 375
      sql = 'select * from "TmpGetDates.dbf"'
      requestLive = false
      active = true
      active = false

Edit this code and change the active=true line to active=false. Now when this report is called from the dialog form (via the Preview form), the render() event will set the active property true and the temporary table will be opened.

Using a ReportViewer Object

The dUFLP’s Preview form is quit useful and many developers include it with their applications. Some developers, however, prefer to preview a report in the same form that selects the report parameters. One example of this type of form is dQuery. The Current Report tab in the lower pane contains a reportViewer object, which displays the selected report.

In this section we discuss a form that combines the functions of the GetDates dialog form and of the Preview form into a single interface. My intention is to focus on the functional elements that make this form work. It is neither to provide a full array of features nor to offer a professional looking form. The hope is that when you understand the functional elements, you can add them to your full-featured form. (And when you do this, you will want to study the various methods in the Preview form.)

The example combo form looks something like the follow image.

The interface controls on this form include a container at the top and a reportViewer underneath. In the container there are two spinboxes for entering the start date and the end date for the report. There are also four pushbuttons that are used to preview the report, move from page to page, and print the report.

The TmpQuery object in this form is created in the form’s Constructor code. In this regard we are following the structure of the ItemMover form. However, the TmpQuery object could alternatively be created in the pushbutton’s onClick() method like we did in the GetDates form.

The TmpQuery’s canOpen() method is the same as its corresponding method in the previous two examples. It adds the field names and field types to an array and then creates the temporary table.

The Preview button in this form is similar to the Print button in the ItemMover form.
Function PBPREVIEW_onClick
   if form.tmpQuery1.rowset.first()
      form.reportViewer1.filename = ""
   local dStatDate,dStopDate,oForm
   oForm = this.parent.parent.parent
   dStartDate = this.parent.parent.spinboxStart.value
   dStopDate  = this.parent.parent.spinboxStop.value
   until not oForm.invoice1.rowset.next()

   form.reportViewer1.params[ "temptable" ] = ;
   form.reportViewer1.filename = "reportViewer.rep"


Like the previous dialog form, this form begins by emptying the temporary table if it already contains data. Notice that in this form we must remove the report from the reportViewer (i.e. assign an empty string to the filename property) before calling the emptyTable() method. This is necessary so that the table is closed when the method runs. Otherwise we will get an error message claiming that the table is in use by another.

After the temporary table is empty the above code restricts the data to the user defined date range and then loops through the rows appending each one to the table.

The final part of the code opens the report in the reportViewer object. This part is different from the code used in the ItemMover form. In that example we had to create a parameter array and pass it to the Preview form. In the current form, however, we need only set two properties of the reportViewer object. First, since the reportViewer object has a built-in params array, we add the “temptable” element to that array. And second we assign the report file to the filename property. This immediately renders the report into the reportViewer object.

The report

The report used in this example is slightly different than the report used with the Preview form examples. The main difference is where the report looks for the parameter array. When using the Preview form, the parameter array is assigned to the form object like this: fPreview.params=params. Then the report’s render() event looks for this array attached to the parent form and assigns it to the report object (this.params=this.reportViewer.form.params).

In the current form our render event can be simplified a bit. This is because the ReportViewer class has a ref property that stores a reference to the report object and the report class has a reportViewer property that stores a reference back to the reportViewer object. Thus any property of the reportViewer can be seen by the report
form.reportViewer1.params <=> report.reportViewer.params

and any property of the report can be read or set by the reportViewer.
form.reportViewer1.ref.startPage <=> report.startPage

This mutual relationship make is possible to simplify the render() method used in the report. The following code example shows the render() event used in the GetDates report with a strike through type for the lines that can be eliminated and bold face type for the additions.
Function form_render
   if type( "this.runOnce" ) # "L"
      this.runOnce = true
      if type( "this.reportViewer" ) == "O"
         if type( "this.reportViewer.form.params" ) == "O"
             this.params = this.reportViewer.form.params
      if type( "this.reportViewer.params" ) == "O" and ;
          this.reportViewer.params.isKey( "temptable" )
          form.tmpGetDates1.active := false
          form.tmpGetDates1.active := true
          form.tmpGetDates1.rowset.indexName := "index1"
   return SUPER::render()

A similar modification must be made to the TmpQuery object’s canOpen() method. Again rather than looking for the parameter array as a property of the report, we look for it as a property of the report’s reportViewer reference.
Function tmpgetdates1_canOpen
   if type( "this.parent.reportViewer.params" ) == "O"
      this.sql = 'select * from "' + ;
      this.parent.reportViewer.params['temptable'] + '.dbf"'
      this.sql = 'select * from "TmpGetDates.dbf"'
   return true

This form should now work.

TmpQuery and Forms

The TmpQuery class works very well with reports and this task is undoubtedly its most common use. However, a TmpQuery object can also be used with a form. The final section of this article will consider two forms that use a TmpQuery object. The first is a data entry form where the user appends data into a temporary table and, once they are confident that the data is correct, posts it to the permanent table. The second form is a type of lookup form. It loads a list of files from a folder into a grid for display to the user.

Data Entry Form

The following image is a representation of the sample data entry form. The concept for this example is taken from a form in one of my applications, which runs at a home health-care agency. Nurses spend their day visiting homebound patients who require skilled nursing care. Each nurse keeps track of their visits on a “day sheet” and a data-entry operator must enter these after they’re submitted. Before posting a day sheet, the data-entry operator must check the validity of the Nurses’ claims and verify that the total number of entries equals the number of visits on the day sheet.

This sample form does not have the complexity of the original. It does, however, include the primary elements for using a TmpQuery object. In this case the TmpQuery object is created in the form’s Constructor code. Once constructed, the rowset works like any normal rowset on a form.

When the form is instanced, the TmpQuery object’s canOpen() method is used to define the fields and create the table.

Function tmpquery1_canOpen
      add("Last Name C20")
      add("First Name C20")
      add("City C30")
      useTempPath = false
      // dropOnClose = false
      createIndex("Last Name")
   return TMPQuery::canOpen()

dBASE executes the query after the canOpen() method is finished. At this point the temporary table is created and the rowset is active. We now can set any of the rowset properties. These are done in the query’s onOpen() event handler. For the example form this is were the indexName is set.

Function tmpquery1_onOpen
   this.rowset.indexName := "Last Name"

After this code executes, the form opens with an empty grid and the user can begin entering data.

When the user is satisfied that the data is correct, it can then be moved to the permanent table. This might be done with a pushbutton, which would move the data and empty the temporary table or it can be done in the form’s onClose() event handler. The sample form uses the latter event.

In the onClose() event handler a query object is created for the permanent table. Then we loop through each row in TmpQuery1 and append each field whose names match in both tables. The very last task is to deactivate TmpQuery1, which deletes the temporary table.


Function form_onClose
   local PermTable
   PermTable = new QUERY()
   with (PermTable)
      // database = form.hlthn1
      sql = "Select * from customer"
      active = true
   if form.TmpQuery1.rowset.first()
         for i = 1 to form.TmpQuery1.rowset.fields.size
            cFieldname = form.TmpQuery1.rowset.fields[i].fieldname
            PermTable.rowset.fields[cFieldname].value =  ;
      until not form.TmpQuery1.rowset.next()
   form.TmpQuery1.active = false


Array Grid Form

Another type of form where a TmpQuery object can be useful is when there’s a need to display the content of an array in a grid. The dBASE grid object can not be datalinked to an array, but, with a TmpQuery object, the array can be stored in a temporary table and the grid can be datalinked. The next example is a form with a grid that displays the result of the array class’s dir() method. This method fills the array with five characteristics of specified files in a folder (i.e. file name, size, modified date, modified time, and file attributes). The grid in the following image displays those characteristics.

The TmpQuery object that is contained in this sample form is created in the Constructor code. The query’s canOpen() event handler defines the fields, creates the temporary table, and creates three indexes. These indexes can be used to sort the contents of the grid by file name, file size or last modified date.

The TmpQuery class does not create index tags in decending order. This is a minor issue and easy to address. My method is to create a subclass of the TmpQuery class — called TmpQuery2 — and add a new method named CreateIndexDecending(). This new method is identical to the CreateIndex() method except for one additional property. It is used in the canOpen() event handler to index the size field in descending order.

The query’s onOpen() event handler is used to read the file characteristics into the array and store them in the temporary table. Thus, by the time the grid is instanced in the constructor code, a table is created and populated. The grid can therefore be datalinked to the TmpQuery object.


The techniques used to create and populate a temporary table should be rather familiar by this point. We have repeated them, with only slight variations, in each of the foregoing example. But, as its been said, repetition is helpful for learning how to apply specific concepts. The concept in this article is how to use temporary tables in your reports and forms. Although temporary tables are not always required, in those situations where they are needed, the TmpQuery class provides some very useful tools for working with them.

The author would like to thank Todd Kreuter for sharing the TmpQuery class and ___ for proofreading the text. The author remains responsible for any errors in this article.