Ayende @ Rahien

Neal Blomfield commented on NH Prof Alerts: Select N + 1

Fri, 09 Jan 2009 00:13:07 GMT

Select N+1 also seems to be caused by specifying lazy = false for the collection in the mapping file. I am guessing that NH2 defaults to using FetchMode.Select if you do not explicitly specify a fetch mode (I need to go read the docs / look at the code but commenting while I remember). Might be worth adding something about this to the alert docs?

Ayende Rahien commented on NH Prof Alerts: Select N + 1

Wed, 07 Jan 2009 11:21:49 GMT

[www.google.co.il/search?q=nhibernate+subselect](http://www.google.co.il/search?q=nhibernate+subselect)

Henning commented on NH Prof Alerts: Select N + 1

Wed, 07 Jan 2009 11:18:40 GMT

OK - so I linked my little playground to the 2.0.1 GA ... so what do I do next :) I mean - how do I this subselect fetching?

Ayende Rahien commented on NH Prof Alerts: Select N + 1

Wed, 07 Jan 2009 06:44:24 GMT

Yes, NH 1.2 doesn't have subselect fetching.

Henning commented on NH Prof Alerts: Select N + 1

Tue, 06 Jan 2009 21:38:39 GMT

... ahh; does it matter that I'm still using NH 1.2? :)

Henning commented on NH Prof Alerts: Select N + 1

Tue, 06 Jan 2009 21:35:33 GMT

maybe I'm missing your point :) what are you trying to tell me by mentioning the "sub select option" - I'm not sure. I did a quick test: I have two orders, one with one orderitem, the otherone with two orderitems. When I do the following: DetachedCriteria criteria = DetachedCriteria.For(typeof (Order)) .SetFetchMode("OrderItems", FetchMode.Select); IList

Ayende Rahien commented on NH Prof Alerts: Select N + 1

Sat, 03 Jan 2009 20:31:32 GMT

Henning, There are many options for eager loading with NH. In this case, you are talking about the sub select option.

Henning commented on NH Prof Alerts: Select N + 1

Sat, 03 Jan 2009 13:57:41 GMT

I might be mistaken, but if I do an eager load, doesn't that like join posts and comments? So when I have like a "bundle" of comments per post, I redundantly retrieve the post-data from the db :( I would rather like two calls to the DB: 1. all the posts 2. get all the comments where the post-id is in the list of post-ids of the posts This would reduce the DB-traffic as much as possible. But how would I do that *painless* with NH? If I would have a methode like "GetAllWithComments()" this could first get all posts, and then issue a second query with a "in"-restriction or something. Or is there a better way?

alberto commented on NH Prof Alerts: Select N + 1

Tue, 30 Dec 2008 17:15:42 GMT

1) Well, if you have N lazy loaded relations there are 2^N possible combinations (hence the method explosion) but you are probably right that in practice YAGNI all those. 2) But the consumers of the repository must now know which of the methods to call. Maybe I'm worrying to much, as it should be obvious (while "1" remains true) depending on what they want. Thanks for the insight!

Ayende Rahien commented on NH Prof Alerts: Select N + 1

Tue, 30 Dec 2008 16:27:18 GMT

1) Yes, it does. In practice, there are only a few ways of processing the graph. 2) There is a big difference, the only code that needs to know about this is the persistence code, not all the rest of the code, as is the case with EF.

alberto commented on NH Prof Alerts: Select N + 1

Tue, 30 Dec 2008 16:19:21 GMT

My concerns with that solution are: 1) Does it really work in more complex, real world apps? Seems like it would lead to method explosion in the repository, polluting the API. 2) It doesn't seem a big difference from a PI point of view to the (openly criticized) "explicit lazy loading" in EF.

Ayende Rahien commented on NH Prof Alerts: Select N + 1

Tue, 30 Dec 2008 14:35:27 GMT

Alberto, You have GetAllWithComments(), or something like that

alberto commented on NH Prof Alerts: Select N + 1

Tue, 30 Dec 2008 13:15:51 GMT

If you have a PostRepository and a GetAll() method that lazy loads Comments. Now you want run into this problem for some scenario. What do you do?

Ayende Rahien commented on NH Prof Alerts: Select N + 1

Mon, 29 Dec 2008 12:37:22 GMT

Alberto, I don't follow you, can you explain further?

alberto commented on NH Prof Alerts: Select N + 1

Mon, 29 Dec 2008 11:04:15 GMT

Indirectly related, I'm not so sure how people deal with this cases when you have a separate DAL (i.e Repositories), maybe a hint would be useful for your users too.

Ayende Rahien commented on NH Prof Alerts: Select N + 1

Mon, 29 Dec 2008 05:57:40 GMT

Steve, Thanks, I updated the docs & the post.

anonymous coward commented on NH Prof Alerts: Select N + 1

Sun, 28 Dec 2008 21:57:35 GMT

I believe a more common name for "Select N+1" is "N+1 selects" antipattern, I don't think there's anything bad in selecting a number N+1 from a database :)

Steve Bohlen commented on NH Prof Alerts: Select N + 1

Sun, 28 Dec 2008 20:27:09 GMT

>>Select N+1 is a data access anti pattern, in which we are accessing the database in the least optimal way. I think this should say 'non-optiimal' or 'sub-optimal' as I'm not 100% certain that I cannot think of an even less-optimal way to access the DB :D >> which are also used to solved the issue of Too Many Queries. Minor point, but I think '...solve the issue of...' is what's meant here (recognizing that english isn't your first language and its my ONLY (non-programming) language, so offering as helpful input, not criticism). Looking (really) forward to this becoming a product I can buy~!