Validation in Entity Framework Code First

23 October 2013

Entity framework code first has support for validation for frequent validation scenarios. In this post, we will look at a couple of ways on how this can be achieved.

If you are new to Entity framework code first, you might want to check out my post on entity framework quick start.

There are two ways on how to do the validation: through data annotations and through the fluent API.

Using Data Annotations

Let’s say that we have a Person entity with the following declaration:

public class Person
{
    public string Name { get; set; }

    // other properties
}

By default, no validation is applied to its properties. Name can be null, empty, or can have any length.

What if you want to set the Name to required? You can just update the model like so:

using System.ComponentModel.DataAnnotations;

public class Person
{
    [Required]
    public string Name { get; set; }

    // other properties
}

With the [Required] attribute, entity framework will check that the Name field has a value before doing in insert or update. If validation fails, an exception will be thrown when calling SaveChanges.

Using the Fluent API

An alternative way to configure the property is through the Fluent API. Following is the fluent API code that achieves the same effect (setting the Name property to required):

public class MyContext : DbContext
{
    public DbSet<Person> People { get; set; }

    protected override void OnModelCreating
        (DbModelBuilder modelBuilder)
    {
        Entity<Person>().Property(p => p.Name).IsRequired();
    }

    // other members
}

Notice that this time around, we are overriding a DbContext method called OnModelCreating. The fluent API call appears inside this method, which reads: “for the Person entity, set the Name property as required.”

There is also one more effect of configuring property validations when using either data annotations or the fluent API. When entity framework creates the database, any string property will automatically be mapped to columns that are nullable (null). However, when marking a property as Required, the associated column will be made not null.