Data Annotations - MaxLength Attribute in EF 6 & EF Core

The MaxLength attribute specifies the maximum length of data value allowed for a property which in turn sets the size of a corresponding column in the database. It can be applied to the string or byte[] properties of an entity.

using System.ComponentModel.DataAnnotations;
    
public class Student
{
    public int StudentID { get; set; }
    [MaxLength(50)]
    public string StudentName { get; set; }
        
}

In the above example, the MaxLength(50) attribute is applied on the StudentName property which specifies that the value of StudentName property cannot be more than 50 characters long. This will create a StudentName column with nvarchar(50) size in the SQL Server database, as shown below.

Entity Framework also validates the value of a property for the MaxLength attribute if you set a value higher than the specified size. For example, if you set more than 50 characters long string value, then EF 6 will throw System.Data.Entity.Validation.DbEntityValidationException and EF Core will throw Microsoft.EntityFrameworkCore.DbUpdateException.

Note: The MaxLength attribute can also be used in ASP.NET MVC to validate the value of a property. Visit Implement Validations in ASP.NET MVC for more information.