Model Validation

In addition to model constraints, you can also provide model validation via column validation attributes or custom validator.

Built-in attributes

Here are some of the built-in column validation attributes:

CreditCard: Validates that the column has a credit card format.
EmailAddress: Validates that the column has an email format.
Phone: Validates that the column has a telephone number format.
RegularExpression: Validates that the column value matches a specified regular expression.
Required: Validates that the field is not null.
StringLength: Validates that a string column value doesn't exceed a specified length limit.
Url: Validates that the column has a URL format.

Error messages

Column validation attributes let you specify the error message to be displayed for invalid input. For example:

C#
VB.Net

[StringLength(8, Message = "Name length can't be more than 8.")]

<StringLength(8, Message = "Name length can't be more than 8.")>

Internally, the attributes call String.Format with a placeholder for the column name and sometimes additional placeholders. For example:

C#
VB.Net

[StringLength(8, Message = "{0} length must be between {2} and {1}.", MinimumLength = 6)]

<StringLength(8, Message = "{0} length must be between {2} and {1}.", MinimumLength = 6)>

When applied to a Name property, the error message created by the preceding code would be "Name length must be between 6 and 8.".

To find out which parameters are passed to String.Format for a particular attribute's error message, see the source code.

Custom attributes

For scenarios that the built-in column validation attributes don't handle, you can create custom validation attributes:

Create a class that inherits from ValidationColumnAttribute;
Override the IsValid method and DefaultMessageString property;
Make sure your custom attribute is correctly decorated with ModelDesignerSpec to be friendly to Model Visualizer.

See the source code of built-in column validation attributes as examples.

Custom validator

Another option for model validation is to implement custom validator with property returns CustomValidatorEntry and a pair of CustomValidatorAttribute and _CustomValidatorAttribute in the model class, as shown in the following example:

C#
VB.Net

[CustomValidator(nameof(VAL_ProductNumber))]
public class SalesOrderInfoDetail : ...
{
    ...
    [_CustomValidator]
    private CustomValidatorEntry VAL_ProductNumber
    {
        get
        {
            string Validate(DataRow dataRow)
            {
                if (ProductID[dataRow] == null)
                    return null;
                var productNumber = Product.ProductNumber;

                if (string.IsNullOrEmpty(productNumber[dataRow]))
                    return string.Format(UserMessages.Validation_ValueIsRequired, productNumber.DisplayName);
                else
                    return null;
            }

            IColumns GetSourceColumns()
            {
                return Product.ProductNumber;
            }

            return new CustomValidatorEntry(Validate, GetSourceColumns);
        }
    }
    ...
}

<CustomValidator("VAL_ProductNumber")>
Public Class SalesOrderInfoDetail
    ...
    <_CustomValidator>
    Private ReadOnly Property VAL_ProductNumber As CustomValidatorEntry
        Get
            Dim validate =
                Function(dataRow As DataRow) As String
                    If ProductID(dataRow) Is Nothing Then Return Nothing
                    Dim productNumber = Product.ProductNumber
                    If String.IsNullOrEmpty(productNumber(dataRow)) Then Return String.Format(My.UserMessages.Validation_ValueIsRequired, productNumber.DisplayName)
                    Return Nothing
                End Function

            Dim getSourceColumns =
                Function() As IColumns
                    Return Product.ProductNumber
                End Function

            Return New CustomValidatorEntry(validate, getSourceColumns)
        End Get
    End Property
    ...
End Class

You can add custom validator by clicking the left top drop down button of Model Visualizer tool window, then click 'Add Custom Validator...':

The following dialog will be displayed:

Fill the dialog form and click "OK", code of a to-be-implemented custom validator will be generated automatically.