EF Core Check Constraint Validation Constraints

The .NET provides various built-in validation attributes, which allow you to use certain constraints on properties. Typically, these attributes are used by web frameworks such as ASP.NET to validate data provided by users but EFCore.CheckConstraints allows you to enforce them in the database as well.

Let's say we have the following Author class.

public class Author
{
    public int AuthorId { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }
    public virtual ICollection<Book> Books { get; set; }
}

When you use the code-first approach, EF Core will generate the following table against the Author class.

CREATE TABLE [dbo].[Authors] (
    [AuthorId] INT            IDENTITY (1, 1) NOT NULL,
    [Name]     NVARCHAR (MAX) NULL,
    [Age]      INT            NOT NULL,
    CONSTRAINT [PK_Authors] PRIMARY KEY CLUSTERED ([AuthorId] ASC)
);

Now we have to add some attributes as shown below.

public class Author
{
    public int AuthorId { get; set; }
    [MinLength(3)]
    public string Name { get; set; }
    [Range(18, 100)]
    public int Age { get; set; }
    public virtual ICollection<Book> Books { get; set; }
}

To register the constraints, we need to call the UseValidationCheckConstraints() method.

public class BookStore : DbContext
{
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder
            .UseSqlServer(@"Data Source=(localdb)\ProjectsV13;Initial Catalog=BookStoreDb;")
            .UseValidationCheckConstraints();
    }

    public DbSet<Author> Authors { get; set; }
    public DbSet<Book> Books { get; set; }
}

Let's execute your code again so that EF regenerates the tables again.

CREATE TABLE [dbo].[Authors] (
    [AuthorId] INT            IDENTITY (1, 1) NOT NULL,
    [Name]     NVARCHAR (MAX) NULL,
    [Age]      INT            NOT NULL,
    CONSTRAINT [PK_Authors] PRIMARY KEY CLUSTERED ([AuthorId] ASC),
    CONSTRAINT [CK_Authors_Age_Range] CHECK ([Age]>=(18) AND [Age]<=(100)),
    CONSTRAINT [CK_Authors_Name_MinLength] CHECK (len([Name])>=(3))
);

As you can see, EF now defines the constraints on the table as well.