# Eager loading by sql **URL:** \ **Category:** Rails\ **Created:** [September 27, 2008, 3:28pm UTC](https://www.ruby-forum.com/t/eager-loading-by-sql/149660 "2008-09-27T15:28:09Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![captaffy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/f04885/32.png) [@captaffy](https://www.ruby-forum.com/u/captaffy)\ **Post date:** [September 27, 2008, 3:28pm UTC](https://www.ruby-forum.com/t/eager-loading-by-sql/149660/1 "2008-09-27T15:28:09Z")
I can see how to do eager loading of associations in the cases where you’re letting AR construct the SQL and passing in :include =\>{:assoc1,:assoc2} and so on. But my case using LEFT OUTER JOIN it generates is mind numbingly slow so I have to hand code my SQL to get an acceptable speed. But doing this means that I can’t see how to get the thing to eager load. The issue is that I have and M2M relationship. model\_1 and model\_2 both have a mutual HABTM relationship. When I select all instances of model\_1 that are linked to a particular instance of model\_2 I also want to see for each instance of model\_1 all the instances of model\_2 that it’s linked to. I can see how to generate such a query by hand coding, and the result set will be something like model\_1.id,model\_1.field\_1, model\_1.field\_2, model\_2.id,model\_2.field\_1 1 avalue anothervalue 20 m2\_value 1 avalue anothervalue 650 m2\_different\_value 1 avalue anothervalue 785 m2\_another\_different\_value and so on. Now that’s the kind of result set that AR must be getting back when it automagically creates SQL for eager loading. So how does it work out to creating 3 instances of model\_2 linked to one instance of model\_1 from the above result set? To eager load the associations given the above result set does AR need to know that the input parameters had an :include in them. Or does it work things out purely from the result set? If it can work purely from a result set then I’ll be able to hand code the SQL. If I have to tap on :include =\>{:something} into automagic SQL creation then I’m stuffed. Any thoughts? John S. ---
**Author:** ![captaffy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/f04885/32.png) [@captaffy](https://www.ruby-forum.com/u/captaffy)\ **Post date:** [September 27, 2008, 5:18pm UTC](https://www.ruby-forum.com/t/eager-loading-by-sql/149660/2 "2008-09-27T17:18:23Z")
On 27 Sep 2008, at 14:28, John S. > To eager load the associations given the above result set does AR need > to know that the input parameters had an :include in them. Or does it > work things out purely from the result set It’s not by inspection of the result set (although it does used a certain well defined set of aliased column names. There’s a plugin called eager finder SQL that claims to allow eager loading with custom SQL. Fred ---
**Author:** ![captaffy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/f04885/32.png) [@captaffy](https://www.ruby-forum.com/u/captaffy)\ **Post date:** [September 27, 2008, 9:10pm UTC](https://www.ruby-forum.com/t/eager-loading-by-sql/149660/3 "2008-09-27T21:10:56Z")
Frederick C. wrote: > It’s not by inspection of the result set (although it does used a > certain well defined set of aliased column names. There’s a plugin > called eager finder SQL that claims to allow eager loading with custom > SQL. > > Fred Perfect, just what I’m looking for. Thanks John S.