Question

Starting with the following LINQ query:

from a in things   where a.Id == b.Id &&   a.Name == b.Name &&   a.Value1 == b.Value1 &&   a.Value2 == b.Value2 &&   a.Value3 == b.Value3   select a; 

How can I remove (at runtime) one or more of the conditions in the where clause in order to obtain queries similar to the following ones:

from a in things   where a.Id == b.Id &&   a.Name == b.Name &&   a.Value2 == b.Value2 &&   a.Value3 == b.Value3   select a; 

Or

from a in things   where  a.Name == b.Name &&   a.Value3 == b.Value3   select a; 

Answer 1

Rather than try to change existing where clauses, I’d refactor it to this:

from a in things   where a.Id == b.Id  where a.Name == b.Name  where a.Value1 == b.Value1 where a.Value2 == b.Value2 where a.Value3 == b.Value3   select a; 

That then becomes:

things.Where(a => a.Id == b.Id)       .Where(a => a.Name == b.Name)       .Where(a => a.Value1 == b.Value1)       .Where(a => a.Value2 == b.Value2)       .Where(a => a.Value1 == b.Value3); 

Now it should be reasonably clear how to proceed – conditionalise the calls to Where:

IQueryable<Whatever> query = things; if (useId) {     query = query.Where(a => a.Id == b.Id); } query = query.Where(a => a.Name == b.Name); if (checkValue1) {     query = query.Where(a => a.Value1 == b.Value1); } // etc