Here is a little trick if you want to issue a query to the database and select a batch of entities by ID only:
//assemble an array of ID values
int[] customerIds= new int[] { 1, 2, 3 };
var customers = from customer in context.CustomerSet
where customerIds.Contains(customer.Id)
select customer;
This will make Entity Framework issue an SQL query with the where clause “where customerId in (1,2,3)”, and thus, you can batch select specific entities with a single query.
I will get back to this idea in a later post because this is related to how I design my entities and aggregates in DDD.
//Rogerr
Roger Johansson Blog 
Actually this is basic Linq query stuff, although it’s hard to do in a Linq provider (as the set contains works on can be a query as well as the parameter passed into contains ;))
EF1.0 lacked this Contains operator, which has always surprised me.
It is pretty annoying that EF v1 lacks support for this. I agree that it’s basic LINQ stuff (no matter how complicated how complicated this is for a LINQ provider).
Any way to get this working in EF v1. How would you handle this?
The best workaround I have found for EF 1 is the following:
//assemble an array of ID values
int[] customerIds= new int[] { 1, 2, 3 };
string customerIdsString = customerIds.ToString(", ");
var customers =
from customer in context.CustomerSet.Where("it.Id in {" + customerIdsString + "}")
select customer;
For this to work correctly you need to add some extension methods as described at codemeit. I found the initial where clause idea from an MSDN thread.
EF translate `customerIds.Contains(customer.Id)` to ` … WHERE (1 = id) AND (2 = id) AND (3 = id) AND … `. It’s realy bad with 10.000 items
thanks its work…….
Is this possible where can pass sql query in ef where ? like that
var query = db.users.where(“username like ‘test user%’ “);