Question

I have started using the entity framework for a web application and would like to know what the best way would be to allow users to filter lists dynamically.
i.e. If we have a list of people the user can filter by lastname, city, etc.

The problem I am having is that I am using EF 4 with code first and all the fitlering I can find is using Linq queries but I can’t see a way to build up the where clause for the filter dymaically based on the filter options the user has selected. i.e. in SQL you could build,

select * from people, address where lastname = 'jones' and address.city = 'sydney'

Is there a way to build up this list dynamically using linq?

EDIT
The solution I’m going to try will be similar to this Implementing Dynamic Searching Using LINQ. As I prefer to be as generic as possible where I can.

Answer 1

The way to do this is for example defining some type for search criteria:

public class PeopleSearchCriteria
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string City { get; set; }
}

and define custom extension method for IQueryable<Person> :

public static IQueryable<Person> FilterBySearchCriteria(this IQueryable<Person> query, 
     PeoplseSearchCritera criteria)
{
    if (!String.IsNullOrEmpty(criteria.FirstName))
    {
        string firstName = criteria.FirstName;
        query = query.Where(p => p.FirstName == firstName);
    }

    // do similar code for other criterias

    return query;
}

Now you only need to create model binder (or use default one if possible) to fill your serach options to PeopleSearchCriteria instance and execute simply:

var data = context.People.FilterBySearchCriteria(searchCriteria).ToList();

If you really want some dynamic approach you can build expression tree manually or check Dynamic Linq (you will lose compile time checks).