ComboBox.ValidationRule property (Access)

Use the ValidationRule property to specify requirements for data entered into a record, field, or control. When data is entered that violates the ValidationRule setting, you can use the ValidationText property to specify the message to be displayed to the user. Read/write String.

Syntax

expression.ValidationRule

expression A variable that represents a ComboBox object.

Remarks

Enter an expression for the ValidationRule property setting and text for the ValidationText property setting. The maximum length for the ValidationRule property setting is 2048 characters. The maximum length for the ValidationText property setting is 255 characters.

For controls, you can set the ValidationRule property to any valid expression. For field and record validation rules, the expression can't contain user-defined functions, domain aggregate or aggregate functions, the Eval function, the CurrentUser method, or references to forms, queries, or tables. In addition, field validation rules can't contain references to other fields. For records, expressions can include references to fields in that table.

For table fields and records, you can also set these properties in Visual Basic by using the DAO ValidationRule property.

Microsoft Access automatically validates values based on a field's data type; for example, Access doesn't allow text in a numeric field. You can set rules that are more specific by using the ValidationRule property.

If you set the ValidationRule property but not the ValidationText property, Access displays a standard error message when the validation rule is violated. If you set the ValidationText property, the text that you enter is displayed as the error message.

For example, when a record is added for a new employee, you can enter a ValidationRule property requiring that the value in the employee's StartDate field fall between the company's founding date and the current date. If the date entered isn't in this range, you can display the ValidationText property message: "Start date is incorrect."

If you create a control by dragging a field from the field list, the field's validation rule remains in effect, although it isn't displayed in the control's ValidationRule property box on the property sheet. This is because a field's validation rule is inherited by a control bound to that field.

Control, field, and record validation rules are applied as follows:

• Validation rules that you set for fields and controls are applied when you edit the data and the focus leaves the field or control.

• Validation rules for records are applied when you move to another record.

• If you create validation rules for both a field and a control bound to the field, both validation rules are applied when you edit data and the focus leaves the control.

The following table contains expression examples for the ValidationRule and ValidationText properties.

If you create a validation rule for a field, Access doesn't normally allow a Null value to be stored in the field. If you want to allow a Null value, add "Is Null" to the validation rule, as in "<> 8 Or Is Null" and make sure that the Required property is set to No.

You can't set field or record validation rules for tables created outside Access (for example, dBASE, Paradox, or SQL Server). For these kinds of tables, you can create validation rules for controls only.

Example

The following example creates a validation rule for a field that allows only values over 65 to be entered. If a number less than 65 is entered, a message is displayed. The properties are set by using the SetFieldValidation function.

Dim strTblName As String, strFldName As String 
Dim strValidRule As String 
Dim strValidText As String, intX As Integer 
 
strTblName = "Customers" 
strFldName = "Age" 
strValidRule = ">= 65" 
strValidText = "Enter a number greater than or equal to 65." 
intX = SetFieldValidation(strTblName, strFldName, _ 
 strValidRule, strValidText) 
 
Function SetFieldValidation(strTblName As String, _ 
 strFldName As String, strValidRule As String, _ 
 strValidText As String) As Integer 
 
 Dim dbs As Database, tdf As TableDef, fld As Field 
 
 Set dbs = CurrentDb 
 Set tdf = dbs.TableDefs(strTblName) 
 Set fld = tdf.Fields(strFldName) 
 fld.ValidationRule = strValidRule 
 fld.ValidationText = strValidText 
End Function

The following example uses the SetTableValidation function to set record-level validation to ensure that the value in the EndDate field comes after the value in the StartDate field.

Dim strTblName As String, strValidRule As String 
Dim strValidText As String 
Dim intX As Integer 
 
strTblName = "Employees" 
strValidRule = "EndDate > StartDate" 
strValidText = "Enter an EndDate that is later than the StartDate." 
intX = SetTableValidation(strTblName, strValidRule, strValidText) 
 
Function SetTableValidation(strTblName As String, _ 
 strValidRule As String, strValidText As String) _ 
 As Integer 
 
 Dim dbs As Database, tdf As TableDef 
 
 Set dbs = CurrentDb 
 Set tdf = dbs.TableDefs(strTblName) 
 tdf.ValidationRule = strValidRule 
 tdf.ValidationText = strValidText 
End Function

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