Data Annotations And Validation In MVC

This is the initial set up and we need to run this data annotation validation project.

Now, we are going to discuss the validation available in data annotation only by one.

Note

Data annotations are the attributes that we can find in the System.ComponentModel.DataAnnotations namespace. These attributes provide Server side validation and the framework also supports client side validation.

Required

We will force the student to give their first name and last name, we can decorate the FirstName and LastName properties of the student Model with required attributes.
When we run the page without giving the FirstName and LastName, we will get error message, as shown below:



These attributes raise a validation error, if either property value is null or empty. Like all the built in validation attributes the required attributes deliver both client side and server side validation.

With these attributes in place, if someone tries to submit the page without proving the FirstName and LastName, they will see the default error, shown above.

Attributes based on validation ensures that our client and server side validation rules are kept in synchronization because they have been declared in one place.

StringLength

We are forcing the user to enter his name but what happens if he enters a name with enormous length? For student LastName, we will set maximum 60 characters that can be entered. Hence, for doing that, we must decorate LastName with StringLength attributes.
When we run the page after entering LastName more than 60 characters, we will get the error message, as shown below:



We notice that we can attack multiple validation attributes on the single properties. MinimumLength is an optional named parameter we can use to specify the minimum length for a string.
Here, last name requires a minimum of four character words.

RegularExpression

Regular expressions are an efficient means to enforce the shape and contains a string value. Suppose, we need to validate the Email ID of the student without sending the Email and Regular expression attributes will do it for us in the way, shown below:
When a user tries to enter an invalid Email ID and submit the page, he will get validation error, as shown below:



We will see how to display user friendly error message in a later part of this article.

Range

The Range attributes specifies the minimum and maximum constrains for a numerical number, as shown below:
In this example, the age for student will be between 10 to 30 years to pass the validation. Here, the first parameter of the attribute is the minimum value and second part is the maximum value. The Range attributes will work with an integer, double and another overloaded versions will take Type as parameters, as shown below:
Compare

Compare to ensure two properties of a model has same value. For example, Email ID and confirm email ID.
If both Email ID and confirm Email ID are not same, the user will get model validation error, as shown below:



Display

Display attribute sets the friendly name for the model properties. We can use the Display attributes to fix the name for label for LastName field.
When we will set the last name display properties then it will look like



ScaffoldColumn

The ScaffoldColumn attribute hides the properties from HTML helper such as EditorForModel and DisplayForModel,
Address will not be shown in UI if ScaffoldColumn is false.

DisplayFormat

DisplayFormat attribute handles formatting option for the properties via named parameters. We can provide an alternative text for display, when property is null. We can also specify data format string, currency symbol etc. Suppose we have student income property for which we want to set currency symbol, which is shown below:
By default, ApplyFormatInEditMode is false because MVC binder might not to parse the value formatted for display only.

ReadOnly

If we decorate an attribute with ReadyOnly attribute, the user can not set that property's value.
DataType

DataType attributes enable us to provide the runtime information about the specific purpose of the properties. For example, a property of type string can have various scenarios as it might hold Email address, URL or a password. There are various data types that includes Currency, Date, Time, Password and MultilineText etc.
When we set DataType as password, we will see the password field in non readable format.



Custom Error Message and Localization

Every validation attribute allows you to pass the name parameter with custom error message. We can configure the default error message with a user friendly error message as we need to pass the custom error message with ErrorMessage named attribute shown below:
If a user will not input the correct Email format, he will get an error, shown below:



The ErrorMessage can also have a single format item in the string. The built in attributes format provide the properties name with a user friendly message.


If we create an Application with globalization and localization features then this string message will be not sufficient. Hence, in this case, we can configure the error message with the resource string.
In this case, ErrorMessage considers a resource file name with LastName as a key for an associated error message.

Validation and Model Binding

By default, ASP.Net MVC framework executes validation logic during model binding. In Controller side, we need to check
We can also use,
We can also check Individual validation, as shown below:
To display the error message in our view, we must need to include following line with all the properties in which we are applying validation.
Conclusion

In this article, we learned about the built in data annotation validation in ASP.Net MVC framework. If you have any question or comments regarding this article, please post it in the comment section of this article. In the next article, we will learn to create a custom validation in ASP.NET MVC. Thank you for reading this article. I hope you like it.