带有多选和子查询的 EF Core CROSS JOIN

Question

I have a problem writing a LINQ query using CROSS JOIN on two tables, and subquery in the result.

I'll show you the SQL query that I made, and it is working in my PostgreSQL Server:

SELECT t2.id, t1.id,
      (
       SELECT COALESCE(avg(t3.value), -1) 
       FROM table3 t3
       LEFT JOIN table4 t4 ON t4.id = t3.tag_id
       LEFT JOIN table5 t5 ON t5.id = t4.device_id
       LEFT JOIN table6 t6 ON t6.id = t4.system_id
       WHERE t4.tag_type_id = 171 --TT Value
       AND t1.id = ANY(t4.control_area)
       AND t6.zone_id = t2.id
       ) 
FROM table1 t1
CROSS JOIN table2 t2
ORDER BY t2.z_index,t1.d_index

And I try now to duplicate this query in EF Core code and this is what I got so far:

var ss = ctx.Table1.SelectMany(
                t1 => ctx.Table2,
                (t1, t2) => new
                {
                    T1 = t1.Id,
                    T2 = t2.Id,
                    Value = ctx.Table3
                            .Include(s => s.Table4.Table5.Table6)
                            .Where(s => s.Table4.TagTypeId == 171 
                                    && s.Table4.Table5.ControlArea.Any(a => a == t1.Id)
                                    && s.Table4.Table5.Table6.Zone == t2.Id)

                }).ToList();

When I run this I get the following error:

Unable to cast object of type 'System.Linq.Expressions.MethodCallExpression2' to type 
'System.Linq.Expressions.LambdaExpression'.

I'm not sure how can I accomplish this without using ctx.Database.ExecuteSqlRaw("SELECT....");

Is there a way to do it?

Thanks in advance, Julian

Answer 1

I was able to solve my problem. I'm posting this answer with hope that it will help others with similar problem. The solution is just to add .Average(s=>s.Value) to the end of the subquery.

Something like this:

var ss = ctx.Table1.SelectMany(
            t1 => ctx.Table2,
            (t1, t2) => new
            {
                T1 = t1.Id,
                T2 = t2.Id,
                Value = ctx.Table3
                        .Include(s => s.Table4.Table5.Table6)
                        .Where(s => s.Table4.TagTypeId == 171 
                                && s.Table4.Table5.ControlArea.Any(a => a == t1.Id)
                                && s.Table4.Table5.Table6.Zone == t2.Id).Average(s=>s.Value)

            }).ToList();