LINQ Join with Multiple Conditions in On Clause

Question

I\'m trying to implement a query in LINQ that uses a left outer join with multiple conditions in the ON clause.

I\'ll use the example of the following two tables

Answer 1

You can't do it like that. The join clause (and the Join() extension method) supports only equijoins. That's also the reason, why it uses equals and not ==. And even if you could do something like that, it wouldn't work, because join is an inner join, not outer join.

Answer 2

You just need to name the anonymous property the same on both sides

on new { t1.ProjectID, SecondProperty = true } equals 
   new { t2.ProjectID, SecondProperty = t2.Completed } into j1

Based on the comments of @svick, here is another implementation that might make more sense:

from t1 in Projects
from t2 in Tasks.Where(x => t1.ProjectID == x.ProjectID && x.Completed == true)
                .DefaultIfEmpty()
select new { t1.ProjectName, t2.TaskName }

Answer 3

Here you go with:

from b in _dbContext.Burden 
join bl in _dbContext.BurdenLookups on
new { Organization_Type = b.Organization_Type_ID, Cost_Type = b.Cost_Type_ID } equals
new { Organization_Type = bl.Organization_Type_ID, Cost_Type = bl.Cost_Type_ID }

Answer 4

This works fine for 2 tables. I have 3 tables and on clause has to link 2 conditions from 3 tables. My code:

from p in _dbContext.Products join pv in _dbContext.ProductVariants on p.ProduktId equals pv.ProduktId join jpr in leftJoinQuery on new { VariantId = pv.Vid, ProductId = p.ProduktId } equals new { VariantId = jpr.Prices.VariantID, ProductId = jpr.Prices.ProduktID } into lj

But its showing error at this point: join pv in _dbContext.ProductVariants on p.ProduktId equals pv.ProduktId

Error: The type of one of the expressions in the join clause is incorrect. Type inference failed in the call to 'GroupJoin'.