Why does replacing the lambda in a IQueryable.Sum selector with a function which creates the lambda fail? (Error 1025)

Question

I wanted to abstract a lambda function I have which sums up records in my DB based on their status. The problem is, when I run the generated lambda against LINQ to Entities, I get "Internal .NET Framework Data Provider error 1025." (FYI, it works fine against LINQ to Objects).

Here's the code:

    <Extension()> _
    Public Function Summarize(ByVal auditsToSummarize As IQueryable(Of HvacAudit)) As IQueryable(Of HvacAuditSummary)
        Return From audit In auditsToSummarize
               Group By month = audit.DateCreated.Value.Month Into g = Group
               Select New HvacAuditSummary With {
                    .GroupingKey = month,
                    .Pending = g.Sum(Function(audit) If(audit.AuditStatusInt = CType(AuditStatus.Pending, Integer), 1, 0)),
                    .Issued = g.Sum(Function(audit) If(audit.AuditStatusInt = CType(AuditStatus.Issued, Integer), 1, 0)),
                    .Closed = g.Sum(Function(audit) If(audit.AuditStatusInt = CType(AuditStatus.Closed, Integer), 1, 0)),
                    .Cancelled = g.Sum(Function(audit) If(audit.AuditStatusInt = CType(AuditStatus.Cancelled, Integer), 1, 0))
                }
    End Function

And here's an example of how I try to use the lambda generator:

    Select New HvacAuditSummary() With {
        .Cancelled = g.Sum(AuditsWithStatus(AuditStatus.Cancelled))
    }

    Private Function AuditsWithStatus(auditStatus As AuditStatus) As Func(Of HvacAudit, Integer)
        Return Function(audit) If(audit.AuditStatusInt = CType(auditStatus, Integer), 1, 0)
    End Function

NOTE: I have looked through other questions with this error, they all seem to focus on using the wrong LINQ because a lambda (Func) was used in place of an expression. In the sum method, all the candidates seem to take a Func, so I don't know what else I can change.

score 1 · Accepted Answer · answered Jul 27 '12 at 22:50

1

The Entity Framework query provider does not know your function AuditsWithStatus. EF tries to translate everything in your linq statement into sql, and it can only handle a restricted set of .Net functions of which it knows the sql equivalent. For the rest everything in the linq statement must be an expression (Expression<Func<...>>).

Which means: you can use your function but only after using ToList() or ToArray(), which turns it into linq-to-objects. Or you must turn your function into an expression.

answered Jul 27 '12 at 22:50

Gert Arnold

105,341
31
202
291

How would I convert the Func to an Expression>? – just.another.programmer Jul 29 '12 at 18:01
1

Try [this link](http://www.digitallycreated.net/Blog/37/dynamic-queries-in-entity-framework-using-expression-trees) or use [PredicateBuilder](http://www.albahari.com/nutshell/predicatebuilder.aspx). – Gert Arnold Jul 29 '12 at 18:42
I wish I could double upvote that comment. Most clear intro to expressions I have seen. Thanks. – just.another.programmer Jul 29 '12 at 20:09

score -1 · Answer 2 · answered Jul 27 '12 at 18:10

-1

Check out your anonymous function.

.Sum is expecting what in C# we'd call a Func<bool>. You're returning 1 or 0, which are implicity either integers or doubles (I forget which, but it's unimportant in the context of your question.)

Long story short - true or false, not 1 or 0!

answered Jul 27 '12 at 18:10

Andrew Gray

3,756
3
39
75

Sum expects a Func which returns the value to add for the specified entity. See documentation here: http://msdn.microsoft.com/en-us/library/bb908057%28v=vs.90%29.aspx – just.another.programmer Jul 29 '12 at 18:03

Why does replacing the lambda in a IQueryable.Sum selector with a function which creates the lambda fail? (Error 1025)

2 Answers2

Linked