Linq optional parameters

Question

I have a linq query. I have a bunch of parameters from a form I collect where I need to filter based of fields the user is searching for.

IQueyable

        

Answer 1

If the query doesn't include a particular field, you don't need to include it as part of the where clause at all:

IQueyable<Users> user = from user in edmxObject.Users;

if (model.FirstName != null) 
    users = users.Where(user => user.FirstName.Contains(model.FirstName)

if (/* age is searched for */) 
    users = users.Where(user => user.Age == model.Age);

You can conditionally nest predicates this way to ensure you have only the conditions you really need.

Answer 2

This is one of the best examples of why LINQ is so powerful - deferred execution. You can build up the query in different phases, and only when the query is finally executed or resolved will the SQL statement be generated:

var query = edmxObject.Users.AsQueryable<Users>();

if (! String.IsNullOrEmpty(model.FirstName)) {
    query = from user in query
            where user.FirstName.Contains(model.FirstName)
            select user;
}
if (! String.IsNullOrEmpty(model.UserName) {
    query = from user in query
            where user.UserName.Contains(model.UserName)
            select user;
}

// this will cause the query to execute get the materialized results
var result = query.ToList();