EF Core StringLength Attribute

The StringLength attribute is applied to a property to specify a maximum number of characters or bytes for the column that the property should map to. The following example specifies that the Title column in the Books table is to be have a maximum length of 150 characters instead of the default which is unlimited:

public class Book
{
    public int BookId { get; set; }
    [StringLength(150)]
    public string Title { get; set; }
    public Author Author { get; set; }
}

The StringLength attribute also allows you to specify a minimum acceptable length for a string:

public class Book
{
    public int BookId { get; set; }
    [StringLength(150, MinimumLength = 5)]
    public string Title { get; set; }
    public Author Author { get; set; }
}

Setting the MinimumLength property value has no effect on database configuration, but can be used to provide client-side validation in validation-aware UI frameworks, such as ASP.NET MVC.

In terms of database configuration, the StringLength attribute works in the same way as the MaxLength attribute. In previous versions of Entity Framework, the MaxLength attribute also enforced entity validation and an exception was raised if the supplied value exceeded the maximum length specified. Entity validation is not included in Entity Framework Core 1.0.

Fluent API

The Fluent API equivalent for the StringLength attribute is the HasMaxLength method.