EF core join with multiple OR conditions

Question

I want to convert this sql query to linq :

select * from  A a
join B b on (    (a.level1= b.PerimeterID and  b.PerimeterLevelID = 1)
              OR (a.level2= b.PerimeterID and  b.PerimeterLevelID = 2)
              OR (a.level3= b.PerimeterID and  b.PerimeterLevelID = 3)
            )

What i tried:

from a in A
join b in B on new {PerimeterID = a.level1, PerimeterLevelID = 1 } equals new { b.PerimeterID, b.PerimeterLevelID }
where (a.level2 == b.PerimeterID && b.PerimeterLevelID == 2) ||
      (a.level3 == b.PerimeterID && b.PerimeterLevelID == 3)

it generate this sql query :

select * from  A a
join B b on (a.level1= b.PerimeterID and  b.PerimeterLevelID = 1)
where (a.level2= b.PerimeterID and  b.PerimeterLevelID = 2)
       OR (a.level3= b.PerimeterID and  b.PerimeterLevelID = 3))

I tried also Linqer but it can't convert OR to linq

SQL cannot be converted to LINQ: OR

what i have to do to convert this sql query

Answer 1

An inner join is equivalent to a filtered crossjoin. So how about

from a in A
from b in B 
where (a.level1 == b.PerimeterID && b.PerimeterLevelID == 1) ||
      (a.level2 == b.PerimeterID && b.PerimeterLevelID == 2) ||
      (a.level3 == b.PerimeterID && b.PerimeterLevelID == 3)
select new {a,b};

?

Answer 2

you can try with DefaultIfEmpty() . Joins will behave like left join with this command

from a in A
from b in B.DefaultIfempty()
where (   (a.level1== b.PerimeterID &&  b.PerimeterLevelID == 1)
       || (a.level2== b.PerimeterID &&  b.PerimeterLevelID == 2)
       || (a.level3== b.PerimeterID &&  b.PerimeterLevelID == 3))

Answer 3

I think that this query will help

var query = from a in context.A
            join b1 in context.B
                on new { Perimeter = a.level1, LevelID = 1 }
                equals new { Perimeter = b1.PerimeterID, LevelID = b1.PerimeterLevelID }
            join b2 in context.B
                on new { Perimeter = a.level2, LevelID = 2 }
                equals new { Perimeter = b2.PerimeterID, LevelID = b2.PerimeterLevelID }
            join b3 in context.B
                on new { Perimeter = a.level3, LevelID = 3 }
                equals new { Perimeter = b3.PerimeterID, LevelID = b3.PerimeterLevelID }
            select new
            {
                a,
                b1,
                b2,
                b3
            };