How do you create a CTE with an IList<> passed as a parameter?

My function currently takes an IList<> as a parameter. I need to be able to convert it to a CTE that is joined on in a SQL statement.

When I try to convert it to an IQueryable object and convert it to a CTE like so:

var myQueryable = myList.asQueryable<T>();
var myCTE = myQueryable.AsCte();

But myCTE object doesn’t reflect having any values from the list.

var myQueryableType = myQueryable .GetType(); 

This shows that the type is System.Linq.EnumerableQuery as well.

The myCTE object also has the message: “There is no method ‘AsCte’ on type ‘LinqToDB.LinqExtensions’ that matches the specified arguments”.

[sdanyliv]

There are only four IQueryable sources supported in library

• GetTable
• FromSql
• SelectQuery
• AsCte

Any of them are complicated. I appreciate your interest but it can be really challenging task from the start. For example implementing CTE took about month of my free time to understand how to do that correctly. It is not an just create SQL AST which generates VALUES, but it is also good knowledge in our LINQ parser.

I’ll give you small example which problems needs to be solved: We have array

var data = new [] {
  new Some 
   { 
    Column1 = ..,
    Column2 = ..,
    ...
    ColumnN = ..,
   },
   ...
},

Let’s write query

var query = 
   from d in data.AsQueryable(db)
   join t1 in db.OtherTable1 on d.Colum1 equals t1.Id
   join t2 in db.OtherTable2 on d.Colum2 equals t2.Id
   select new { t1, t2 }

In this query, we have used only two fields from data array. So only two fields should be used in SQL generation. Another trick with reusing values from other table:

var query = 
   from m in db.Master
   from d in new Some[] {
     new Some{Column1 = m.Id, Column2 = 1},
     new Some{Column1 = m.Id2, Column2 = m.Value}
     new Some{Column1 = 1, Column2 = 2}
   }
   join t1 in db.OtherTable1 on d.Colum1 equals t1.Id
   join t2 in db.OtherTable2 on d.Colum2 equals t2.Id
   select new { t1, t2 }

Also If database do not support VALUES, we have to mimic it by UNION ALL A lot of nuances here. Really. That’s why i’m trying to prioritize this task implementation.

If you still interested, i can start pointing you in right direction.

[viceroypenguin]

Yeah, I’m going to write a series of new tests for sure. Need to test that the constant array works for insert, update, delete, merge, and regular select. I’ll put in [ActiveIssue] tests for all of the same for the outer apply version, knowing those won’t work in v1.

Thanks for the add’l places to look for changes though.