Check out example codes for "how to use more than one condition in ef join". It will help you in understanding the concepts better.

Code Example 1

var query = from x in context.table1 
             join y in context.table2 on 
             new  {
                  Key1 = x.col1, 
                  Key2 = x.col2,
                  Key3 = true,
                  Key4 = true
                 }
             equals
             new {
                  Key1 = y.key1, 
                  Key2 =  y.key2,
                  Key3 = y.from_date< DateTime.Now,
                  Key4 = !y.deleted
                 }  
             into result
from r in result.DefaultIfEmpty()
select new  {x.Something, r.Something}

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