ASP.NET-Identity limit UserName length

问题

How can I limit the UserName field in the table AspNetUsers?

Neither this:

public class ApplicationUser : IdentityUser
{
    [Required, MaxLength(15)]
    public string UserName { get; set; }

}

or this:

modelBuilder.Entity<ApplicationUser>().Property(x => x.UserName).HasMaxLength(15);

works.

I need this because setting an Index on an nvarchar(max) gives me this error msg:

Column 'UserName' in table 'dbo.AspNetUsers' is of a type that is invalid for use as a key column in an index.

To be verbose, I was trying to set the indexes like this:

public override void Up()
{
    CreateIndex("dbo.AspNetUsers", "UserName", true, "IX_UserName");
}

public override void Down()
{
    DropIndex("dbo.AspNetUsers", "IX_UserName");
}

回答1:

In the latest version released today, this should do the trick:

modelBuilder.Entity<ApplicationUser>().Property(x => x.UserName).HasMaxLength(15);

回答2:

Try this

public class ApplicationUser : IdentityUser
{
    [Required, MaxLength(15)]
    public override string UserName { get; set; }

}

回答3:

A lot of time has passed, but I think someone may still find it useful. I've had the same problem and found a clue to my solution here. The migration mechanisms ignore the MaxLength attribute, but one can add the corrections manually:

public override void Up()
{
    AlterColumn("dbo.AspNetUsers", "UserName", c => c.String(nullable: false, maxLength: 15, storeType: "nvarchar"));
    CreateIndex("dbo.AspNetUsers", "UserName");
}

public override void Down()
{
    DropIndex("dbo.AspNetUsers", new[] { "UserName" });
    AlterColumn("dbo.AspNetUsers", "UserName", c => c.String(nullable: false, maxLength: 256, storeType: "nvarchar"));
}

After update-database the fields are shortened and the SQL queries searching by UserName run faster (at least with mySQL which I use), because the indexes are used to search efficiently.

来源：https://stackoverflow.com/questions/21975717/asp-net-identity-limit-username-length