Constraints form - Completing the Constraints tab
Record the computations that constrain the property values. Each row defines a separate constraint. Enter at least one row. Order is not significant.
When the system detects that a constraint fails, it adds a message to the page of the property identified in the left portion of the Require That field (if any). The presence of this message ordinarily prevents the system from saving the page containing this property value to the database.
You can cause a specific additional message ( Rule-Message rule type) to become associated with that property or another property when the constraint fails, in the Else row.
Detection of this message and any later processing to correct the constraint — such as displaying a message to a user, recalculation of the property value, and so on — is an application responsibility.
Each property involved in the constraint expression must be on the primary page (the page that has the class corresponding to the Applies To key part), or on an embedded page identified in Page Context field on the Pages & Classes tab, or on a linked property page.
Using the controls
Click any constraint to enable controls.
| open icon ||Click to review a property (for a field that contains a property reference). If the property does not exist, click the Open icon to create a new property.|
|expression selector||Click the drop-down button to display a drop-down list of all boolean expressions.|
|row buttons||Select any constraint to enable. Click the Add a row icon to add a new constraint, or click the Delete this row icon to delete the selected constraint. (Equivalently, use the Insert, Shift+Insert, and Delete keys.)|
|Display Label|| When reviewing this tab, you can see a presentation using either property names or the Short Description ( |
Modifying constraints with drag and drop operations
To move a constraint to a different location, click and drag the small circle located to the left of the entry.
To copy a constraint, drag the entry while holding down the
|When|| Click the drop-down button to select a boolean expression from the drop-down list. The form changes to reflect the expression selected. |
Most expressions require properties. Use SmartPrompt to select a property. You can enter a linked property reference here.
|Require that|| This area defines the constraint. Click the drop-down button to select an expression from the drop-down list. The form changes to reflect the expression selected. |
Most expressions require properties. Use SmartPrompt to select a property, or enter a linked property reference.
You can't specify single elements of a
|Else add message|| Optional. Type the text of a message within quotes or use the SmartPrompt to select the name of a Rule-Message. The list of options is limited to |
Some messages require parameters. To provide fill-in-the-blank text values for each parameter, follow the message name with a backslash character, the single letter t, and text for each message parameter.
|to|| Optional. Identify the property to be marked with the message. The message remains until this property has a new value (or until an activity performs a Page-Clear-Messages method). |
Ordinarily, choose the property that failed the constraint. Some constraints involve two or more properties, on the same or different pages. Select the one most likely to have a new value that will restore the constraint condition.
For example, if the constraint is of the form
then the message can be associated with the BoxWidth property. If the constraint has the form
then the message can be associated with either property.
In unusual cases, you can leave this blank. When you leave this blank, the message is associated with the entire page rather than a property on that page. However, this is temporary, as page messages are removed upon the next user HTTP Submit operation.
You can't use symbolic page names (such as