Question

I’m trying to reduce the number of database queries and in doing so I’m attempting to retrieve a series of hierarchical entities (that were previously fetched recursively) in one go.

I’ve got a Labels property holding a set of strings:

public string[] Labels { get; set; } // new string[] {"{{a}}", "{{b}}", "{{c}}", "{{d}}", "{{e}}"};

that I’m using to construct a first query:

var IDeferredTopLabels= 
    db.labels
        .Where(l =>
            l.site_id == this.site_id &&
            this.Labels.Contains(l.name_for_code)
        )
    .Select(l => new LabelWithParentId { Label = l, ParentId = null });

The above, if inspected while debugging, would generate the following TSQL

SELECT [t0].[id], [t0].[name_for_code], [t0].[site_id], [t0].[priority_level]
FROM [dbo].[labels] AS [t0]
WHERE ([t0].[site_id] = 15) AND ([t0].[name_for_code] IN ('{{a}}', '{{b}}', '{{c}}', '{{d}}', '{{e}}')) 

So far so good, following the IDeferredToplabels declaration I’m extending the first query with a Union specifying how child Label entities should be fetched:

var IDeferredWithChildLabels = IDeferredTopLabels
    .Union(
        db.label__labels
        .Where(ll => 
            db.labels
                .Where(l =>
                    l.site_id == this.site_id &&
                    this.Labels.Contains(l.name_for_code)
                )
            .Select(l => l.id)
            .Contains(ll.parent_label_id)
        )
    .Select(ll => new LabelWithParentId { Label = ll.label1, ParentId = ll.parent_label_id})
    );

Now if I inspect the TSQL generate is:

SELECT [t4].[id], [t4].[name_for_code], [t4].[site_id], [t4].[priority_level], [t4].[value] AS [ParentId]
FROM (
    SELECT [t0].[id], [t0].[name_for_code], [t0].[site_id], [t0].[priority_level], NULL AS [value]
    FROM [dbo].[labels] AS [t0]
    WHERE ([t0].[site_id] = 15) AND ([t0].[name_for_code] IN ('{{a}}', '{{b}}', '{{c}}', '{{d}}', '{{e}}'))
    UNION
    SELECT [t2].[id], [t2].[name_for_code], [t2].[site_id], [t2].[priority_level], [t1].[parent_label_id] AS [value]
    FROM [dbo].[label__label] AS [t1]
    INNER JOIN [dbo].[labels] AS [t2] ON [t2].[id] = [t1].[label_id]
    WHERE EXISTS(
        SELECT NULL AS [EMPTY]
        FROM [dbo].[labels] AS [t3]
        WHERE ([t3].[id] = [t1].[parent_label_id]) AND ([t3].[site_id] = 15) AND ([t3].[name_for_code] IN ('{{a}}', '{{b}}', '{{c}}', '{{a}}'0, '{{a}}'1))
        )
    ) AS [t4]

If you see at the end of this second TSQL Query, the part IN ('{{a}}', '{{b}}', '{{c}}', '{{a}}'0, '{{a}}'1)), the set of strings have some unespected 0 and 1 next to the second last and last element plus it is no longer the initial set of strings (ie ‘{{a}}’, ‘{{b}}’, ‘{{c}}’, ‘{{d}}’, ‘{{e}}’) but instead '{{a}}', '{{b}}', '{{c}}', '{{a}}', '{{a}}'.

What I’m I doing wrong!?

I’m clueless, I appreciate your help, thank you.

EDIT:

I just tried to use an int[] and compare the id rather then the name_for_code and I’m still getting 1 and 0 appended to the last 2 elements of the array as well as the array elements are wrong:

SELECT [t4].[id], [t4].[name_for_code], [t4].[site_id], [t4].[priority_level], [t4].[value] AS [ParentId]
FROM (
    SELECT [t0].[id], [t0].[name_for_code], [t0].[site_id], [t0].[priority_level], NULL AS [value]
    FROM [dbo].[labels] AS [t0]
    WHERE ([t0].[site_id] = 15) AND ([t0].[id] IN (1, 2, 3, 4, 5))
    UNION
    SELECT [t2].[id], [t2].[name_for_code], [t2].[site_id], [t2].[priority_level], [t1].[parent_label_id] AS [value]
    FROM [dbo].[label__label] AS [t1]
    INNER JOIN [dbo].[labels] AS [t2] ON [t2].[id] = [t1].[label_id]
    WHERE EXISTS(
        SELECT NULL AS [EMPTY]
        FROM [dbo].[labels] AS [t3]
        WHERE ([t3].[id] = [t1].[parent_label_id]) AND ([t3].[site_id] = 15) AND ([t3].[id] IN (1, 2, 3, 10, 11))
        )
    ) AS [t4]

Answer 1

OK I found the problem and actually it was not happening when running the code but only in debug mode and specifically it seems it is a bug in Scott Gu’s LINQ to SQL Debug Visualizer

That is why the TSQL that I was grabbing was not parameterized, @David B you made a very good point!

I will leave a comment on Scott Gu’s page pointing to this question.

Thanks all!