EF db-first can't infer constraints from database.
Use the MaxLenght
data annotation attribute:
public partial class Registrant
{
public Registrant()
{
}
public int id { get; set; }
public string fname { get; set; }
[MaxLength(3, ErrorMessage = "")]
public string mid_initial { get; set; }
public string lname { get; set; }
}
Note: this class is a auto generated class and every time you update and save your model (.EDMX file), this code will be overwritten and you'll loose your attributes.
To avoid that, you should extend your classes with some partial classes with the same name and same namespace as your auto-generated classes. If you need examples to show you how, tell me to put it in answer.