Linq dynamic queries for user search screens

Question

I have a database that has a user search screen that is \"dynamic\" in that I can add additional search criteria on the fly based on what columns are available in the partic

Answer 1

As for your first question, you can do this using Dynamic Linq as described by Scott Gu here

var query = Northwind.Products.Where("Lastname LIKE "test%");

Answer 2

I'm not sure how detailed your dynamic query needs to be, but when I need to do dynamic queries, I create a class to represent filter values. Then I pass that class to a search method on my repository. If the value for a field is null then the query ignores it. If it has a value it adds the appropriate filter.

public class CustomerSearchCriteria{
    public string LastName { get; set; }
    public string FirstName { get; set; }
    public string PhoneName { get; set; }
}


public IEnumberable<Customer> Search(CustomerSearchCriteria criteria){
    var q = db.Customers();

    if(criteria.FirstName != null){
        q = q.Where(c=>c.FirstName.Contains(criteria.FirstName));
    }

    if(criteria.LastName!= null){
        q = q.Where(c=>c.LastName.Contains(criteria.LastName));
    }

    if(criteria.Phone!= null){
        q = q.Where(c=>c.Phone.Contains(criteria.Phone));
    }
    return q.AsEnumerable();
}