Using dynamic where clauses in Entity Framework

Question

I am trying to re-design a data access layer that was originally built using Raptier. Raptier generats methods that accept a where clause as a parameter to be passed in to a stored proc. I really need to retain the existing mesthos signatures, so my new DAL needs to accept where clauses as well. I want to use the more up-to-date data access technologies and techniques, so was thinking about using Entity Framework from .Net 4.0.

However, it doesn't look like I can accept dynamic where clauses without implementing some intense reoutines to parse them into lamba expressions. Is there something I've missed? Am I out of luck with Entity Framework?

Thanks, Marc

Answer 1

Two ideas come in mind.

1). Dynamic LINQ, which allows you to define where operators as strings.

var result = Northwind.Products
    .Where("CategoryId=2 And UnitPrice>3")
    .OrderBy("SupplierId");

2). Use something as the EntityFilter<T> (see code here), which allows you to define a filter like this:

IEntityFilter<Person> entityFilter =
    from person in EntityFilter<Person>.AsQueryable()
    where person.Name.StartsWith("a")
    where person.Id < 100
    select person;

You can supply the IEntityFilter<Person> to a business method that will be able to filter that query:

public static Person[] GetAllPersons(
    IEntityFilter<Person> filter)
{
    using (var db = ContextFactory.CreateContext())
    {
        IQueryable<Person> filteredList =
            filter.Filter(db.Persons);

        return filteredList.ToArray();
    }
}