These attributes will not be lost when you regenerate the model classes because the metadata attribute is applied in partial classes that are not regenerated. By applying the metadata attribute to the partial class, you ensure that the data validation attributes will be applied to the automatically-generated class. Notice that each class is marked as a partial class, and each matches the name and namespace as the class that is automatically generated. Replace the contents of the file with the following code. In the Models folder, add a class named PartialClasses.cs. Now, you must associate the model classes with the metadata classes. The Display attribute is used to change the value used for text labels. These metadata classes contain all of the validation attributes that you had previously applied to the model classes. Replace the code in Metadata.cs with the following code. In the Models folder, add a class named Metadata.cs. In this approach, the model class can be regenerated without losing all of the attributes that have been applied to the metadata class. When you associate the model class to the metadata class, those attributes are applied to the model. To avoid this problem, you can add a metadata class that contains the attributes. This approach can be very inefficient and prone to losing important validation rules. Add metadata classesĪdding the validation attributes directly to the model class works when you do not expect the database to change however, if your database changes and you need to regenerate the model class, you will lose all of the attributes you had applied to the model class. You will receive this error: The field Grade must be between 0 and 4. Click List of enrollments and select Edit. If you attempt to enter more than 50 characters, an error message is displayed. Public Nullable EnrollmentDate Ĭlick List of students and select Edit. Add the following highlighted code to the class. Select Models > ContosoModel.edmx > ContosoModel.tt and open the Student.cs file. ![]() You will also restrict Grade to values between 0 and 4. If a user provides more than 50 characters for one of those values, the page will crash when attempting to save the value to the database. In the database, these values are limited to 50 characters however, in your web application that character limit is currently not enforced. In this tutorial, you will add data annotations to restrict the length of the values provided for the FirstName, LastName, and MiddleName properties. You can also apply formatting attributes that change how the properties are displayed such as, changing the value used for text labels. These annotations are applied throughout your web application for the specified property. To specify more data validation rules, you can add data annotations to your model class. For example, you can only provide a number for the Grade property. A class like the following would be a step towards hiding some complexity.As you saw in an earlier topic, some data validation rules are automatically applied to the user input. I recommend you bend it to your will and build something that makes it easy to use inside your specific design and architecture. Like everything framework related, the Validator tries to provide an API that will work in a number of validation scenarios. Public IEnumerable Validate( ValidationContext validationContext) The Validator also works with self validating objects that implement IValidatableObject. The Validator also executes any custom attributes you have defined, and for custom attributes you might find the serviceProvider useful as a service locator, while the items parameter is a dictionary of extra data to pass along. You can construct the ValidationContext class without a service provider or items collection, as shown in the above code, as they are optional for the built-in validation attributes. Var isValid = Validator.TryValidateObject(recipe, context, results) įoreach ( var validationResult in results)Ĭonsole.WriteLine(validationResult.ErrorMessage) ![]() Var context = new ValidationContext(recipe, serviceProvider: null, items: null) You could validate the recipe with the following code: var recipe = new Recipe() For example, let's say you have the following class in a console mode application: public class Recipe Specifically, there is a static Validator class to execute the validation rules. ![]() The assembly contains everything you need to execute validation logic in the annotations. Several people have asked me about using data annotations for validation outside of a UI framework, like ASP.NET MVC or Silverlight.
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