how to translate method call into lambda expression

Question

I have a question about LinqToSql approach.

Model:

public class Person
{
    public int ID { get; set; }
    public string LastName { get; set; }
    public Phone Phone { get; set; }
}

public class Phone
{
    public int ID { get; set; }
    public string Number { get; set; }

    public bool IsUkr()
    {
        return this.Number.StartsWith("380");
    }
}

I use Nhibernate as ORM and I want to execute

IQueryable<Phone> phones = session.Query<Phone>().Where(x => x.IsUkr());

But Nhibernate can't translate this expression into sql because it doesn't know about method IsUkr().

Solution is to write some wrapper to IQueryable interface and use:

session.Query<Phone>().ToExpandable().Where ....

But I don't understand how translate LambdaExpression x => x.IsUkr() into
x => x.Number.StartsWith("380")

Can someone help me?

If this is a routine check you may consider making this a computed property in the database table. — Gert Arnold, Oct 24 '17 at 20:39
@GertArnold Thanks for idea. But there are many conditions like this to other properties in model, so this approach is not very good — Тарануха Юрій, Oct 24 '17 at 20:53
I'm not sure what you are looking for, but you can take a look at https://stackoverflow.com/a/26922208/1486443 — Najera, Oct 25 '17 at 19:56

score 0 · Answer 1 · answered Oct 25 '17 at 06:21

0

Take a look at this answer: https://stackoverflow.com/a/13679572/5126411

IsUkr criteria is specific for the Phone entity so you can just add a static method like this:

public static Expression<Func<Phone, bool>> IsUkr = x => x.Number.StartsWith("380");

and use it:

IQueryable<Phone> phones = session.Query<Phone>().Where(Phone.IsUkr);

Maybe it would be better to create a special static class for such methods/properties.

answered Oct 25 '17 at 06:21

Roman Koliada

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It's good idea and it works. But I want to know is it possible to create such expression at runtime – Тарануха Юрій Oct 25 '17 at 08:40

how to translate method call into lambda expression

1 Answers1