Entity Framework Code-First（9.6）：DataAnnotations

DataAnnotations - StringLength Attribute:

StringLength attribute can be applied to a string type property of a class. EF Code-First will set the size of a column as specified in StringLength attribute. Note that it can also be used with ASP.Net MVC as a validation attribute.

Consider the following example.

using System.ComponentModel.DataAnnotations;

public class Student
{
    public Student()
    { 
        
    }
    public int StudentID { get; set; }
     
    [StringLength(50)]
    public string StudentName { get; set; }
        
}

As you can see in the above code, we have applied StringLength attribute to StudentName. So, Code-First will create a nvarchar(50) column StudentName in the Student table as shown below.

Entity Framework also validates the value of a property for StringLength attribute if you set the value more than the specified size. For example, if you set more than 50 chars long StudentName then EF will throw EntityValidationError.