Attach string where condition in linq query

Question

string StrWhere = string.Empty;
StrWhere = " AND ID =5";
String StrQuery ="SELECT * FROM CITY_MAS WHERE + StrWhere";

I want to achieve the same in LINQ. Something along the lines of the following query...

var result = from c in db.CITY_MAS   
         where + StrWhere
         select new { c.ID,c.Name)

Answer 1

You can use Dynamic Linq to dynamically add criteria.

See http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx

Answer 2

You can either use DynamicLINQ (works also with LINQ to SQL) - see Maarten's post - or you can use the following method:

The ObjectQuery<T> contains a Where method that allows to define a string custom predicate. So, your query could be re-written as follows:

var strWhere = "it.ID = 5";
var result = objSet.Where(strWhere);

In the where clause the it refers to the current object/table - analogous to this in c#. The objSet is an ObjectSet<CITY> (which inherits from ObjectQuery<T> ).

Depending, whether you use an ObjectContext or a DbContext the ways to get to objSet are different:

• ObjectContext

In an ObjectContext CITY already would be an ObjectSet<CITY> so there is no real additional action needed, so:

var objSet = db.CITY;

• DbContext (EF Code First)

Here CITY is a DbSet<CITY> and the described override for the Where method is not available. However, each DbContext has an underlying ObjectContext you can use to do some more complex queries. You just have to get to it and then create the ObjectSet :

// assuming: using System.Data.Entity.Infrastructure;

var var objContext = ((IObjectContextAdapter)ctx).db;
var objSet = objContext.CreateObjectSet<CITY>();

See also this blog post for additional uses. Full documentation on the ObjectSet<T>.Where method can be found here .