c# - Dynamic query with OR conditions in Entity Framework

Question

I am creating an application that searches the database and allows the user to dynamically add any criteria (around 50 possible), much like the following SO question: Creating dynamic queries with entity framework. I currently have working a search that checks each criteria, and if it is not blank it adds it to the query.

C#

var query = Db.Names.AsQueryable();
  if (!string.IsNullOrWhiteSpace(first))
      query = query.Where(q => q.first.Contains(first));
  if (!string.IsNullOrWhiteSpace(last))
      query = query.Where(q => q.last.Contains(last));
  //.. around 50 additional criteria
  return query.ToList();

This code produces something similar to the following in sql server (I simplified for easier understanding)

SQL

SELECT
    [Id],
    [FirstName],
    [LastName],
    ...etc
FROM [dbo].[Names]
WHERE [FirstName] LIKE '%first%'
  AND [LastName] LIKE '%last%'

I am now trying to add a way to generate the following SQL with C# through entity framework but with an OR instead of an AND, while still keeping the ability to add criteria dynamically.

SQL

SELECT
    [Id],
    [FirstName],
    [LastName],
    ...etc
  FROM [dbo].[Names]
WHERE [FirstName] LIKE '%first%'
  OR [LastName] LIKE '%last%' <-- NOTICE THE "OR"

Usually the criteria wont be larger than two or three items for a query but combining them into one gigantic query is not an option. I have tried concat, union, and intersect and they just all duplicate the query and join them with UNION.

Is there a simple and clean way to add "OR" conditions to a dynamically generated query using entity framework?

Edit with my solution - 9/29/2015

Since posting this, I have noticed this has received a little attention, so I decided to post my solution

// Make sure to add required nuget
// PM> Install-Package LinqKit

var searchCriteria = new 
{
    FirstName = "sha",
    LastName = "hill",
    Address = string.Empty,
    Dob = (DateTime?)new DateTime(1970, 1, 1),
    MaritalStatus = "S",
    HireDate = (DateTime?)null,
    LoginId = string.Empty,
};

var predicate = PredicateBuilder.False<Person>();
if (!string.IsNullOrWhiteSpace(searchCriteria.FirstName))
{
    predicate = predicate.Or(p => p.FirstName.Contains(searchCriteria.FirstName));
}

if (!string.IsNullOrWhiteSpace(searchCriteria.LastName))
{
    predicate = predicate.Or(p => p.LastName.Contains(searchCriteria.LastName));
}

// Quite a few more conditions...

foreach(var person in this.Persons.Where(predicate.Compile()))
{
    Console.WriteLine("First: {0} Last: {1}", person.FirstName, person.LastName);
}

Answer 1

You're probably looking for something like Predicate Builder which allows you to control the AND's and OR's of the where statement easier.

There's also Dynamic Linq which allows you to submit the WHERE clause like a SQL string and it will parse it into the correct predicate for a WHERE.