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Validate the fields of a form

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  • When users enter data in a form and click a submit button, check if the data is valid. If the data seems valid, the app can continue. If not, you should tell the users which fields contain the errors and how to fix them.

    For example, if your users need to enter their emails in the field, and they enter their name instead — that information isn't valid. You can use the built-in capabilities of the app to show the error message and ask the users to retry.

    The client-side validation improves the user experience because it's quick feedback about information users enter in the form. However, you should always check the data that comes from the client side before you save that data to the database.

    Most of this document applies to Reactive Web App and Mobile App. For Traditional Web App, see Validation in Traditional Web.

    Using accelerators to create initial validation flow

    In OutSystems low-code approach, the automatic client-side form validation is provided by default for the supported data types. To use the built-in validations, you need to:

    1. Set the data types of the values in the form. You can do this manually or scaffold the form fields from Entity.
    2. Set the fields as mandatory, if required.
    3. Trigger an accelerator to create a new Client Action with initial validation flow. To automatically create the logic, select the New Client Action from the Event list of the element that submits the data inside the form. Check this example step to create a new Action for a Button.

    Set an input field as mandatory

    The field is mandatory if users must enter a value in that field. To set a field as mandatory, select the widget and in the Properties pane set the Mandatory property to True. Widgets have the Mandatory field, for example, Input Widget or ButtonGroup Widget, if their common use case requires it.

    Mandatory property of the input widget

    Set the data type of a form field

    To automatically check whether the value user enters is valid, you first need to tell the app which value you expect. Select the data type from the Input Type list in the properties of the widget. There are several Data Types you can choose from, such as Integer, Currency, Date, Time, Email.

    Data type of the input value

    Enable or disable the built-in validation

    To activate the built-in client-side validation, set the Built-In Validations property of the Event that submits the data to Yes. For example, On Click Event of a Button Widget or a Link Widget that calls a Client Action.

    Event with Built-In Validations set to on

    Validate the data in a Client Action

    With the built-in validation enabled, you can access the boolean Valid property of the Form Widget in the Client Action that submits the form. For example, if you have a form ReorderItemForm, and a user submits correct data, the value of ReorderItemForm.Valid is True. If a check for any of the fields fails, the value of ReorderItemForm.Valid is False.

    In this example, an If node has ReorderItemForm.Valid in the Condition. If the value of Valid is False, the validation fails and the False branch of the If flow runs.

    The If Node evaluates Valid boolean form the form

    The app validates only the fields you set as mandatory. The app skips the fields that you don't set as mandatory, as those fields are then optional.

    Customizing validation error and warning messages

    Here are some ways to edit the validation messages.

    Editing the default validation messages

    You can edit the default validation messages on the module level. Go to the module properties by clicking the module name (1) in any of the main Service Studio tabs (Process, Interface, Logic, or Data). Then, edit the messages in the Validation Messages section (2).

    The list of the default validation messages

    Changing the field validation messages programmatically

    You can change the validation messages for fields during the execution of the app. You do that by assigning a text value to the ValidationMessage of the widget. Keep in mind that the message only shows after the validation fails, when the value of Field.Valid is False.

    Editing the validation message for a field

    Examples of the client-side validation with accelerators

    There are two examples of the client-side validation in this section.

    Auto-creation of form fields with predefined data types

    Insert fields in forms using a low-code accelerator, which can help you be more efficient when you're using Entity as the data source. Follow the steps below.

    1. Drag a Form Widget to the Screen.
    2. Drag an Entity to the Form Widget. The fields of the form populate automatically.
    3. Go through the fields and set Mandatory to Yes for all fields that aren't optional.
    4. Select the Save button. In the button properties, in the Events section, from the On Click list select New Client Action. A new Action opens, with a default validation logic.
    5. Add different logic when Form.Valid is True or False.

    You can create the form, fields, and the save button, as in this Screen, by dragging an Entity to a Form.

    Auto-created form with data types set for fields

    Step by step example

    Service Studio creates the initial logic for validation automatically, which can speed up your work significantly. Here is a step by step example of creating validation logic. There is a Screen in the app, where users can reorder an item after entering the following information:

    • Name — string, optional
    • Email — email address, mandatory
    • Quantity — integer, mandatory

    Here are the steps to create the UI and basic logic.

    1. Create a new app and add a Screen. Name the Screen "ReorderItemScreen".
    2. Create three Local Variables, and set their properties like this:

      Name Data Type
      EmployeeName Text
      EmployeeEmail Email
      Quantity Integer

      It should look like this, with the Local Variables (1) and entered Name (2) and Data Type (3) properties.

      Local variables in Screen

    3. Drag a Form Widget to the Screen and name it "ReorderItemForm".

    4. Drag three Input Widgets to the "ReorderItemForm", and set the properties like this:

      Name Variable Mandatory
      Input_EmployeeName EmployeeName No
      Input_EmployeeEmail EmployeeEmail Yes
      Input_Quantity Quantity Yes

      Notice how the Input Type property changes automatically to match the Variable data type.

    5. Drag a Button Widget to the form, below the input fields. Set the label of the button as "Reorder". At the end of this step you should have something like this:

      Local variables in Screen

      There is a form (1), and in it the input fields (2) with the properties (3). The button (4) needs to be inside the form.

      Add labels on top of the input fields by dragging a Label Widget above the Input Widget.

    6. Select the button, go to the properties, find the Event section, and in it On Click. Open the On Click list and select New Client Action. New action triggers an accelerator to create a Client Action with an initial validation flow.

      New client Action for On Click

      If you go back to the Screen, you can see that Service Studio created the "ReorderOnClick" Client Action (1). Select the "Reorder" button (2) and confirm that the Built-In Validation property in the Events section has the value Yes (3).

      Low-code created by an automated action

    7. Finally, edit the flow to show an error message if the user enters invalid data, and a success message when the data is valid. Open the ReorderOnClick and it should look something like this:

      Initial flow for validation

      Drag a Message node from the toolbox to the False branch of the If node. Enter "Check if all fields have the correct information and then retry." in the Message property of the Message node, and in the Type list select Error (1). Drag another Message node from the toolbox, this time to the True branch. Enter ""Item reordered!"" and in the Type list select Success (2).

      Validation flow with success and error messages in nodes

    8. Publish and run the app. If you enter valid data, you now get the success message:

      All validations pass

      However, if you enter an email in an unsupported format, or a float instead of an integer, you get the error message:

      A field validations failed

      Note that the name field is optional.

    Creating custom validation logic

    The built-in validation for supported data types works automatically as long as you provide information about the expected data type.

    If you need to extend the validation mechanism for more complex scenarios, create your validation logic and set the Valid variables of the widget fields. If you invalidate any of the fields in the form, that invalidates the entire form (the value of Form.Valid is False).

    Example of custom validation

    In this example, the form contains a field to enter a date for a shipment. The validation logic checks if the date is in the past (1), and if it is, the app marks the field as not valid (2) by setting Input_Date.Valid=False. For better user experience, set a custom message in Input_Date.ValidationMessage, telling users that the date can't be in the past (2).

    Custom date validation logic

    Invalidating the date field invalidates the entire form (3), and shows the custom message next to the field. Also, there's an extra feedback message on top of the screen (4), before the end of the flow. If the validation logic passes successfully, the app calls the Server Action to finalize the request by the user (5).

    Here is the custom validation message in the app running in a browser, with a custom validation message (1) and the feedback message after the form validation failed (2).

    Custom validation message while the app is running

    Validation in Traditional Web

    This section applies to the Traditional Web Apps, where validation runs on the server side.

    To implement the form validations, use server action that the app calls after submitting the form data. Add all validations at the beginning of the flow:

    1. For each validation:
      1. Add the logic to validate the input value.
      2. If the validation fails, assign the input's runtime properties as follows:
        • Input.Valid = False
        • Input.ValidationMessage = "<your error message>"
    2. Check the value of Form.Valid after all input validations. If an inputs isn't valid, the form is also not valid:
      1. Add an If element with the following condition: Form.Valid
      2. If True, continue the action flow.
      3. If False, end the action flow. The form displays validation messages next to all inputs that aren't valid.

    Form validation in Traditional

    The Valid property of the form is False when:

    • Built-in validation for any field fails
    • You assign False to the Valid property of any field of the form

    The validation messages show next to all fields with invalid inputs.