Is it possible to express a check constraint?

问题

I'm doing code-first development with Entity Framework 4.3 and it doesn't seem like it's possible to express a CHECK constraint via attribute annotations or, well, any other means. I see that EF 5.0 will be adding support for checking enumerations, but that's not exactly what I'm after here.

To give a simplified example, I'd like to validate that all Person objects have a first name of either "Bob" or "Harry" and are either 5, 10 or 30 years old.

public class Person
{
    [Required]
    [Check("Bob", "Harry")]  //yes, this attribute is imaginary
    public string FirstName { get; set; }

    [Required, Check(5, 30, 50)]  //check is still imaginary
    public int Age { get; set; }
}

I can run an alter script to add these constraints after the fact and I can roll my own check attribute to perform validations, but is there a way I'm missing to actually express non-enumerated CHECK constraints in Entity Framework?

回答1:

You could write one yourself (untested):

public class CheckAttribute : System.ComponentModel.DataAnnotations.ValidationAttribute
{
    object[] ValidValues;

    public CheckAttribute<T>(params T[] validValues)
    {
        ValidValues = validValues;
    }

    public override bool IsValid(object value)
    {
        return ValidValues.FirstOrDefault(v => v.Equals(value)) != null;
    }
}

回答2:

I've been wanting to put Check constraints in, and while there are a couple of ways to do it like the answer given here by M.Babcock and using the ExecuteSql in the Initializer to add constraints to the database manually.

But I think the easiest method is to use a RegularExpression annotation, so in your example you'd go:

public class Person
{
    [Required]
    [RegularExpression(@"Bob|Harry")]  
    public string FirstName { get; set; }

    [Required, RegularExpression(@"5|30|50")]  
    public int Age { get; set; }
}

来源：https://stackoverflow.com/questions/9588606/is-it-possible-to-express-a-check-constraint