Apply dynamic where clause to joined table

I need to build a LINQ query that allows me to vary the where clause on a joined table but can't find a way to do it.

A simplified example of the two queries I'm constructing are:

var myQuery = from tab1 in context.Table1
           开发者_高级运维   join tab2 in context.Table2 on Table1.ID equals Table2.Table1ID
              where tab1.TypeCode == 3
                    tab2.SomeID == 4 &&  
              select tab1.ID;

var myQuery2 = from tab1 in context.Table1
              join tab2 in context.Table2 on Table1.ID equals Table2.Table1ID
              where tab1.TypeCode == 3
                    tab2.SomeOtherID == 4 &&  
              select tab1.ID;

The only difference between them being the tab2.SomeID where clause changes to tab2.SomeOtherID.

If the changing where clause was being applied to tab1 I could just add a .Where to the query but how do I use a common query and specify a different tab2 where clause?

Dynamically Composing Expression Predicates

or

You need something like this? Use the Linq Dynamic Query Library (download includes examples).

Check out ScottGu's blog for more examples.

You can have optional parameters in queries:

int? someID = null;
int? someOtherID = 4;

var myQuery = from tab1 in context.Table1 
              join tab2 in context.Table2 on Table1.ID equals Table2.Table1ID 
              where tab1.TypeCode == 3 
               && (someID == null || tab2.SomeID == someID)
               && (someOtherID == null || tab2.SomeOtherID == someOtherID)
              select tab1.ID;

Linq-to-SQL will eliminate the parts that can be evaluated client-side from the query, so in the above example the where clause will filter on tab1.TypeCode and tab2.SomeOtherID.