Q:

union of different types using linq2db

I have type definition of DocumentField_1 & DocumentField_2, which is totally different.  
DocumentField_1 has records if assigned value is true otherwise record will not be there, so it is of boolean type.  and DocumentField_2 has value with date.  
I have following query in sql which I want to write using linq2db.  
What is the way to do that having said that those are of different types (boolean & date)?  
select 'True' from DocumentField_1 where DocumentField_1.DocumentId = 2
union all
select CONVERT(varchar, value) from DocumentField_2 where DocumentField_2.DocumentId = 2

schema of DocumentField_1 is 
Id          -> int
DocumentId  -> int

schema of DocumentField_2 is 
Id          -> int
DocumentId  -> int
Value       -> datetime

A:

If I understand your question correctly, it should be simple:
subquery1.Select(_ => “True”).UnionAll(subquery2.Select(_ => _.Date. ToString());

Instead of ToString(), you can also use Sql. Convert / Sql. Convert2 extensions to customize format

