ObjectSet's Where() method and memory

Question

I'm using an ObjectSet's methods to do various queries in a table, namely, selecting a few records from it as such:

    var results = Repository.Find(c => c.Enabled == 1).ToList();

Here is the Find method of my repository:

    public IEnumerable<T> Find(Func<T, bool> predicate)
    {
        try
        {
            return _objectSet.Where<T>(predicate);
        }
        catch
        {
            throw;
        }
    }

Now, if there is about 1,000,000 records in the targeted table, I can see the process's memory usage grow quite a lot even if the Find call I'm doing should return a few records at most.

It seems all the records are pulled client side, then filtered. This is obviously not what I want LINQ to do.

Do you see anything obviously wrong with what I'm doing ?

Thanks in advance.

don't use IEnumerable it is pulling every datarow at once into memory instead you should use IQueryable — MUG4N, Feb 08 '13 at 15:09
Your `Find` method accomplishes nothing productive at all. Why are you not just using `Where` directly on the `Repository`? — Servy, Feb 08 '13 at 15:11
@MUG4N He's only using that for his output, which should already be filtered, so that's not the problem. — Servy, Feb 08 '13 at 15:12

Matthias Meid · Accepted Answer · 2013-02-08T15:52:55.127

2

I think you should use Expression<Func<T, bool>> instead of a plain Func<T, bool>:

public IEnumerable<T> Find(Expression<Func<T, bool>> predicate) {
  // your code
}

Where is overloaded (see ObjectSet Class), and the Func<T>-overload is defined by IEnumerable<T>, whereas Expression<TDelegate> is used by IQueryable<T>. Because predicate is a Func<T> the compiler invokes the extension method defined for IEnumerable<T>, which in turn fetches all the records and does LINQ to objects.

edited Feb 08 '13 at 15:52

answered Feb 08 '13 at 15:10

Matthias Meid

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From which namespace is Expression ? System.Linq.Expressions ? – Francis Ducharme Feb 08 '13 at 15:40
Then I must be doing something wrong because I get this: The non-generic type 'System.Linq.Expressions.Expression' cannot be used with type arguments Using the generic type 'System.Linq.Expressions.Expression' requires 1 type arguments – Francis Ducharme Feb 08 '13 at 15:45
I see. Excuse me, I was wrong. Basically it's an `Expression>` instead of an `Expression`. I edited my answer, and I'll double-check. – Matthias Meid Feb 08 '13 at 15:53
Right, I found another example through Google that worked. Thanks. – Francis Ducharme Feb 08 '13 at 15:58
Now it should be right, isn't it? I double-checked on my Visual Studio 2012 installation. – Matthias Meid Feb 08 '13 at 15:59
Yes it is. Windows Task Manager also shows the process not growing to an outrageous size! Kudos. – Francis Ducharme Feb 08 '13 at 16:18

ObjectSet's Where() method and memory

1 Answers1