LINQ : Convert anonymous type to another anonymous type C#

Question

I want to extend LINQ query based on some conditions.

Actually I am writing a dynamic search functionality where user can select any field and can search. Here if user selects a field that is not available in default LINQ query then I want to extend existing LINQ Query.

For Example

var query = 
    from tbl1 in context.Table1
    join tbl2 in context.Table2 on tble1.Id equals tble2.tble1Id
    where tble1.IsDeleted == false;

And If User Selects a field that cannot be searched in this above query then I want to extend "query" variable as below.

query = query
    .GroupJoin(context.table3, 
        a => new { contactId = a.contact.Id, formId = a.contact.FormIdFK }, 
        DynamicFieldData => new { contactId = DynamicFieldData.EntityIdFK, formId = DynamicFieldData.FormIdFK }, 
        (x, y) => new { a = x, DynamicFieldData = y })
    .SelectMany(x => x.DynamicFieldData.DefaultIfEmpty(),(x, y) => new { a = x.a, DynamicFieldData = y })
    .AsQueryable();

And At the end I can apply dynamic Where Claus on above finalized query.

But when I try to assign updated query to "query" variable it says.

Errror: system.linq.iqueryable <some anonymous type 1 > cannot be implicitly converted to system.linq.iqueryable <some anonymous type 2 >

Answer 1

Usually I use the following pattern:

// apply join
var withOtherTable = 
    from q in query
    join t in context.table3 on ... equals ... into gj
    from t in gj.DefaultIfEmpty()
    select new { q, t };

// apply filters
withOtherTable = withOtherTable.Where(x => x.t.SomeField == "some");

// back to original query
query = withOtherTable.Select(x => x.q);