Validating Data in a LightSwitch Application

Article
03/27/2017

For the latest documentation on Visual Studio 2017, see Visual Studio 2017 Documentation.

This lesson shows how to validate the data that a user enters in a LightSwitch application. For example, in your LightSwitch application, you might want to verify that a telephone number contains the correct number of digits or that a required field isn't empty.

Adding Data Validation

In almost any application that involves data input, the data must be validated before it's saved.

The Data Designer contains an example of one kind of validation: Every entity field has a Required check box. If a field is empty but marked as required, LightSwitch displays a warning when the user tries to save the data.

You can also handle validation in LightSwitch by usingproperties that specify minimum or maximum values for a field, or by writing custom validation code.

To set minimum or maximum values

In Solution Explorer, open the shortcut menu for the Contacts.lsml node, and then choose Open.
In the Data Designer, on the Perspective bar, choose Server.
Choose the <Add Property> link and enter ContactState.
In the Type column, choose String.
In the Required column, clear the check box to mark the ContactState property as optional.
In the Properties window, set the Maximum Length property to 2.

This setting ensures that users can enter no more than two characters in the ContactState field.

To add custom validation code

In Solution Explorer, open the shortcut menu for the Order_Details.lsml node, and then choose Open.
In the Data Designer, on the Perspective bar, choose Server, and then choose the Quantity field.
In the Properties window, choose the Custom Validation link.

The Code Editor opens, and a code block for the Quantity_Validate method appears.
Add the following code to the Quantity_Validate method immediately under the comment line.

Warning

Add either Visual Basic or C# code, depending on the programming language that you chose when you created the project.
```
If Quantity < 1 Then  
    results.AddPropertyError("Quantity must be greater than zero.")  
End If  
```
```
if (Quantity < 1)   
{  
    results.AddPropertyError("Quantity must be greater than zero.");  
}  
```
This code triggers a validation error if a user tries to save a value that's less than one in the Quantity field.

Closer Look

This lesson showed how to validate data by setting validation properties or by writing validation code. You can set different properties for different data types. For example, a String type has a Maximum Length property, and an Integer has Minimum Value and Maximum Value properties. All types have an Is Required property, which is used for the Required check box in the Data Designer.

The validation properties for the Customers entity appear dimmed and can't be changed. Some fields such as Address already have a value in the Maximum Length property. You can’t set validation properties for an entity from an attached data source; you can set them only in the entities that you create.

You can add validation for an entity from an attached data source by writing your own validation code. You can’t override existing validation properties unless you're adding more restrictive validation. For example, for a field that has a Maximum Length of 30, you can’t add validation code to set the length to 40. However, you could add code to restrict the length to less than 30.

Next Steps

In the next lesson, you’ll learn how to add computed properties to data entities.

Next lesson: Adding a Computed Property