EF6 has two ways to where you can add constraints to your model. One of them is Fluent API and the other one is Data Annotations.
In this blog post, we will look into the Fluent API. When you use Fluent API you keep your model class very clean. You don’t have to add any attributes to properties in your model class.
Let’s say that we have a class Student and we want to add constraints to LastName property. This property should be not null and should have not more than 100 characters.
public class Student
{
public int ID { get; set; }
public string LastName { get; set; }
public string FirstMidName { get; set; }
}
To fulfill your requirements about LastName property we should add the following code to the OnModelCreating method in your DbContext class.
public class SchoolContext : DbContext
{
public SchoolContext() : base("SchoolContext")
{
}
public DbSet<Student> Students { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<Student>()
.Property(s => s.LastName)
.IsRequired()
.HasMaxLength(100);
}
}
As you can see in the previous example you can add constraints directly in the OnModelCreating method but if you have a lot of them it would be a little illegible. Entity Framework allows you to create a separate class with model configuration. This new class should inherit from EntityTypeConfiguration. Below you can see configuration class for the Student class.
public class StudentEntityConfiguration: EntityTypeConfiguration<Student>
{
public StudentEntityConfiguration()
{
Property(p => p.LastName)
.IsRequired()
.HasMaxLength(100);
}
}
As you can see above, this code is very similar to this one from the OnModelCreating method. If you have created this custom configuration class, in the next step you need to add this class to Configurations property of the DbModelBuilder in the OnModelCreating method.
public class SchoolContext : DbContext
{
public SchoolContext() : base("SchoolContext")
{
}
public DbSet<Student> Students { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Configurations.Add(new StudentEntityConfiguration());
}
}
And that’s it. Now you can create separate configuration classes to increase the readability and maintainability of your code.