Converting sql statement that contains 'with' cte to linq

Question

Hey, I have this piece of code here, been battling with it for hours. basically what this sql statement does is gets ALL subfolders of a specified folder (@compositeId).

WITH auto_table (id, Name, ParentID) AS
(
SELECT
    C.ID, C.Name, C.ParentID
FROM Composite_Table AS C
    WHERE C.ID = @compositeId

UNION ALL

SELECT
    C.ID, C.Name, C.ParentID
FROM Composite_Table AS C
    INNER JOIN auto_table AS a_t ON C.ParentID = a_t.ID
)

SELECT * FROM auto_table

This query would return something like this:

• Id | Name | ParentId
• 1 | StartFolder| NULL
• 2 | Folder2 | 1
• 4 | Folder3 | 1
• 5 | Folder4 | 4

Now i want to convert the code to linq. I know it involves some form of recursion but still stuck thanks to the with statement. Help?

Answer 1

There is no Linq to SQL equivalent that can do that (in an efficient manner). Best solution would be to call a SP/View/UDF from Linq containing that statement.

Answer 2

You could write code (recursive or not) that repeatedly queries the database, until it has all the results.

But I think there is no way to write a single LINQ to SQL query that would get all the results you need in one go, so it's probably best to keep the query in SQL.

Answer 3

public static List<Composite> GetSubCascading(int compositeId)
{
    List<Composite> compositeList = new List<Composite>();

    List<Composite> matches = (from uf in ctx.Composite_Table
    where uf.Id == compositeId
    select new Composite(uf.Id, uf.Name, uf.ParentID)).ToList();

    if (matches.Any())
    {
        compositeList.AddRange(TraverseSubs(matches));
    }

    return compositeList;
}

private static List<Composite> TraverseSubs(List<Composite> resultSet)
{
    List<Composite> compList = new List<Composite>();

    compList.AddRange(resultSet);

    for (int i = 0; i < resultSet.Count; i++)
    {
        //Get all subcompList of each folder
        List<Composite> children = (from uf in ctx.Composite_Table
        where uf.ParentID == resultSet[i].Id
        select new Composite(uf.Id, uf.Name, uf.ParentID)).ToList();

        if (children.Any())
        {
            compList.AddRange(TraverseSubs(children));
        }
    }

    return compList;
}

//All where ctx is your DataContext