Adding Validation to the Model | Microsoft Docs
Note: An updated version of this tutorial is available here that uses ASP.NET MVC 5 and Visual Studio 2013. It's more secure, much simpler to follow and demo...
Adding Validation to the Model
[!NOTE] An updated version of this tutorial is available here that uses ASP.NET MVC 5 and Visual Studio 2013. It's more secure, much simpler to follow and demonstrates more features.
In this section you'll add validation logic to the
Movie model, and you'll ensure that the validation rules are enforced any time a user attempts to create or edit a movie using the application.
Keeping Things DRY
One of the core design tenets of ASP.NET MVC is DRY ("Don't Repeat Yourself"). ASP.NET MVC encourages you to specify functionality or behavior only once, and then have it be reflected everywhere in an application. This reduces the amount of code you need to write and makes the code you do write less error prone and easier to maintain.
The validation support provided by ASP.NET MVC and Entity Framework Code First is a great example of the DRY principle in action. You can declaratively specify validation rules in one place (in the model class) and the rules are enforced everywhere in the application.
Let's look at how you can take advantage of this validation support in the movie application.
Adding Validation Rules to the Movie Model
You'll begin by adding some validation logic to the
Open the Movie.cs file. Add a
using statement at the top of the file that references the
Notice the namespace does not contain
System.Web. DataAnnotations provides a built-in set of validation attributes that you can apply declaratively to any class or property.
Run the application and you will again get the following run time error:
The model backing the 'MovieDBContext' context has changed since the database was created. Consider using Code First Migrations to update the database (https://go.microsoft.com/fwlink/?LinkId=238269).
We will use migrations to update the schema. Build the solution, and then open the Package Manager Console window and enter the following commands:
When this command finishes, Visual Studio opens the class file that defines the new
DbMIgration derived class with the name specified (AddDataAnnotationsMig), and in the
Up method you can see the code that updates the schema constraints. The
Genre fields are no longer nullable (that is, you must enter a value) and the
Rating field has a maximum length of 5.
The validation attributes specify behavior that you want to enforce on the model properties they are applied to. The
Required attribute indicates that a property must have a value; in this sample, a movie has to have values for the
Price properties in order to be valid. The
Range attribute constrains a value to within a specified range. The
StringLength attribute lets you set the maximum length of a string property, and optionally its minimum length. Intrinsic types (such as
decimal, int, float, DateTime) are required by default and don't need the
Code First ensures that the validation rules you specify on a model class are enforced before the application saves changes in the database. For example, the code below will throw an exception when the
SaveChanges method is called, because several required
Movie property values are missing and the price is zero (which is out of the valid range).
Having validation rules automatically enforced by the .NET Framework helps make your application more robust. It also ensures that you can't forget to validate something and inadvertently let bad data into the database.
Here's a complete code listing for the updated Movie.cs file:
Validation Error UI in ASP.NET MVC
Re-run the application and navigate to the /Movies URL.
Click the Create New link to add a new movie. Fill out the form with some invalid values and then click the Create button.
Globalize.parseFloat. The following code shows the modifications to the Views\Movies\Edit.cshtml file to work with the "fr-FR" culture:
A real benefit is that you didn't need to change a single line of code in the
MoviesController class or in the Create.cshtml view in order to enable this validation UI. The controller and views you created earlier in this tutorial automatically picked up the validation rules that you specified by using validation attributes on the properties of the
Movie model class.
You might have noticed for the properties
Genre, the required attribute is not enforced until you submit the form (hit the Create button), or enter text into the input field and removed it. For a field which is initially empty (such as the fields on the Create view) and which has only the required attribute and no other validation attributes, you can do the following to trigger validation:
- Tab into the field.
- Enter some text.
- Tab out.
- Tab back into the field.
- Remove the text.
- Tab out.
The above sequence will trigger the required validation without hitting the submit button. Simply hitting the submit button without entering any of the fields will trigger client side validation. The form data is not sent to the server until there are no client side validation errors. You can test this by putting a break point in the HTTP Post method or using the fiddler tool or the IE 9 F12 developer tools.
How Validation Occurs in the Create View and Create Action Method
You might wonder how the validation UI was generated without any updates to the code in the controller or views. The next listing shows what the
Create methods in the
MovieController class look like. They're unchanged from how you created them earlier in this tutorial.
The first (HTTP GET)
Create action method displays the initial Create form. The second (
[HttpPost]) version handles the form post. The second
Create method (The
HttpPost version) calls
ModelState.IsValid to check whether the movie has any validation errors. Calling this method evaluates any validation attributes that have been applied to the object. If the object has validation errors, the
Create method re-displays the form. If there are no errors, the method saves the new movie in the database. In our movie example we are using, the form is not posted to the server when their are validation errors detected on the client side; the second
Create method calls
ModelState.IsValid to check whether the movie has any validation errors.
You can set a break point in the
Below is the Create.cshtml view template that you scaffolded earlier in the tutorial. It's used by the action methods shown above both to display the initial form and to redisplay it in the event of an error.
Notice how the code uses an
Html.EditorFor helper to output the
<input> element for each
Movie property. Next to this helper is a call to the
Html.ValidationMessageFor helper method. These two helper methods work with the model object that's passed by the controller to the view (in this case, a
Movie object). They automatically look for validation attributes specified on the model and display error messages as appropriate.
What's really nice about this approach is that neither the controller nor the Create view template knows anything about the actual validation rules being enforced or about the specific error messages displayed. The validation rules and the error strings are specified only in the
Movie class. These same validation rules are automatically applied to the Edit view and any other views templates you might create that edit your model.
If you want to change the validation logic later, you can do so in exactly one place by adding validation attributes to the model (in this example, the
movie class). You won't have to worry about different parts of the application being inconsistent with how the rules are enforced — all validation logic will be defined in one place and used everywhere. This keeps the code very clean, and makes it easy to maintain and evolve. And it means that you'll be fully honoring the DRY principle.
Adding Formatting to the Movie Model
Open the Movie.cs file and examine the
Movie class. The
System.ComponentModel.DataAnnotations namespace provides formatting attributes in addition to the built-in set of validation attributes. We've already applied a
DataType enumeration value to the release date and to the price fields. The following code shows the
Price properties with the appropriate
DataType attributes are not validation attributes, they are used to tell the view engine how to render the HTML. In the example above, the
DataType.Date attribute displays the movie dates as dates only, without time. For example, the following
DataType attributes don't validate the format of the data:
The attributes listed above only provide hints for the view engine to format the data (and supply attributes such as <a> for URL's and <a href="mailto:EmailAddress.com"> for email. You can use the RegularExpression attribute to validate the format of the data.
An alternative approach to using the
DataType attributes, you could explicitly set a
DataFormatString value. The following code shows the release date property with a date format string (namely, "d"). You'd use this to specify that you don't want to time as part of the release date.
Movie class is shown below.
Run the application and browse to the
Movies controller. The release date and price are nicely formatted. The image below shows the release date and price using "fr-FR" as the culture.
The image below shows the same data displayed with the default culture (English US).
In the next part of the series, we'll review the application and make some improvements to the automatically generated