Question

I am playing with a basic implementation of the Query Object “pattern” (in quotes since this is an implementation of the interpreter pattern), and I was thinking of an enhancement which I do not know how to implement.

As you know a Criterion object would look something like the following:

public class Criterion
{
  ...
  string FieldName { get; set; }
  string Value { get; set; }
  ....
}

What I do not like is the fact that I have to add the field a string so I was thinking if I could create some kind of generic Criterion class so I could use it like so:

var criterion = new Criterion<Person>();
criterion.Field = c => c.FirstName;
criterion.Value = "John";

or something along those lines.

Of course there also would be the part where the criteria needs to be converted into SQL so I could do something like:

string query = "SELECT * FROM Person WHERE " + criteria.Field.ToString() + " = '" + criteria.Value + "'"

I am sure there’s got to be a way of doing this but I just can’t wrap my head around it.

Thanks for your help.

Answer 1

You can pretty easily do this with Expressions. This article has an example – Get property name and type using lambda expression