Adding Validation | Microsoft Docs
by Rick Anderson
[!INCLUDE Tutorial Note]
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. Notice the
System.ComponentModel.DataAnnotations 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. (It also contains formatting attributes like DataType that help with formatting and don't provide any validation.)
StringLength attribute sets the maximum length of the string, and it sets this limitation on the database, therefore the database schema will change. Right click on the Movies table in Server explorer and click Open Table Definition:
In the image above, you can see all the string fields are set to NVARCHAR (MAX). 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 (
DataAnnotations), and in the
Up method you can see the code that updates the schema constraints:
Genre field is no longer nullable (that is, you must enter a value). The
Rating field has a maximum length of 5 and
Title has a maximum length of 60. The minimum length of 3 on
Title and the range on
Price did not create schema changes.
Examine the Movie schema:
The string fields show the new length limits and
Genre is no longer checked as nullable.
The validation attributes specify behavior that you want to enforce on the model properties they are applied to. The
MinimumLength attributes indicates that a property must have a value; but nothing prevents a user from entering white space to satisfy this validation. The RegularExpression attribute is used to limit what characters can be input. In the code above,
Rating must use only letters (white space, numbers and special characters are not allowed). 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. Value types (such as
decimal, int, float, DateTime) are inherently required 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 a DbEntityValidationException exception when the
SaveChanges method is called, because several required
Movie property values are missing:
The code above throws the following exception:
Validation failed for one or more entities. See 'EntityValidationErrors' property for more details.
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.
Validation Error UI in ASP.NET MVC
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. As soon as jQuery client side validation detects the error, it displays an error message.
[!NOTE] to support jQuery validation for non-English locales that use a comma (",") for a decimal point, you must include the NuGet globalize as described previously in this tutorial.
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. Test validation using the
Edit action method, and the same validation is applied.
The form data is not sent to the server until there are no client side validation errors. You can verify this by putting a break point in the HTTP Post method, by using the fiddler tool, or the IE 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) checks
ModelState.IsValid to see whether the movie has any validation errors. Getting this property evaluates any validation attributes that have been applied to the object. If the object has validation errors, the
Create method redisplays the form. If there are no errors, the method saves the new movie in the database. In our movie example, the form isn't posted to the server when there are validation errors detected on the client side; the second
Create method gets
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.
Using DataType Attributes
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
The DataType attributes 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. The DataType attribute is used to specify a data type that is more specific than the database intrinsic type, they are not validation attributes. In this case we only want to keep track of the date, not the date and time. The DataType Enumeration provides for many data types, such as Date, Time, PhoneNumber, Currency, EmailAddress and more. The
DataType attribute can also enable the application to automatically provide type-specific features. For example, a
mailto: link can be created for DataType.EmailAddress, and a date selector can be provided for DataType.Date in browsers that support HTML5. The DataType attributes emits HTML 5 data- (pronounced data dash) attributes that HTML 5 browsers can understand. The DataType attributes do not provide any validation.
DataType.Date does not specify the format of the date that is displayed. By default, the data field is displayed according to the default formats based on the server's CultureInfo.
DisplayFormat attribute is used to explicitly specify the date format:
ApplyFormatInEditMode setting specifies that the specified formatting should also be applied when the value is displayed in a text box for editing. (You might not want that for some fields — for example, for currency values, you might not want the currency symbol in the text box for editing.)
You can use the DisplayFormat attribute by itself, but it's generally a good idea to use the DataType attribute also. The
DataType attribute conveys the semantics of the data as opposed to how to render it on a screen, and provides the following benefits that you don't get with
- The browser can enable HTML5 features (for example to show a calendar control, the locale-appropriate currency symbol, email links, etc.).
- By default, the browser will render data using the correct format based on your locale.
- The DataType attribute can enable MVC to choose the right field template to render the data (the DisplayFormat if used by itself uses the string template). For more information, see Brad Wilson's ASP.NET MVC 2 Templates. (Though written for MVC 2, this article still applies to the current version of ASP.NET MVC.)
If you use the
DataType attribute with a date field, you have to specify the
DisplayFormat attribute also in order to ensure that the field renders correctly in Chrome browsers. For more information, see this StackOverflow thread.
[!NOTE] jQuery validation does not work with the Range attribute and DateTime. For example, the following code will always display a client side validation error, even when the date is in the specified range:
You will need to disable jQuery date validation to use the Range attribute with DateTime. It's generally not a good practice to compile hard dates in your models, so using the Range attribute and DateTime is discouraged.
The following code shows combining attributes on one line:
In the next part of the series, we'll review the application and make some improvements to the automatically generated