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author | John Mileham <jmileham@gmail.com> | 2011-03-24 15:03:08 -0400 |
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committer | John Mileham <jmileham@gmail.com> | 2011-03-24 15:03:08 -0400 |
commit | b44a0ec153c84384e9b97a069e81f28bc5c2a4bf (patch) | |
tree | 94713aff0c241f91530dfd714bf685019c84ccab /railties/guides/source/active_record_querying.textile | |
parent | d5994ee48af14d67f0eec7d23863d4b19211b078 (diff) | |
parent | 5214e73850916de3c9127d35a4ecee0424d364a3 (diff) | |
download | rails-b44a0ec153c84384e9b97a069e81f28bc5c2a4bf.tar.gz rails-b44a0ec153c84384e9b97a069e81f28bc5c2a4bf.tar.bz2 rails-b44a0ec153c84384e9b97a069e81f28bc5c2a4bf.zip |
Merge branch 'master' of github.com:rails/rails into count_behavior
Diffstat (limited to 'railties/guides/source/active_record_querying.textile')
-rw-r--r-- | railties/guides/source/active_record_querying.textile | 18 |
1 files changed, 17 insertions, 1 deletions
diff --git a/railties/guides/source/active_record_querying.textile b/railties/guides/source/active_record_querying.textile index 64a68f7592..009d541106 100644 --- a/railties/guides/source/active_record_querying.textile +++ b/railties/guides/source/active_record_querying.textile @@ -420,7 +420,7 @@ Client.limit(5).offset(30) will return instead a maximum of 5 clients beginning with the 31st. The SQL looks like: <sql> -SELECT * FROM clients LIMIT 5, 30 +SELECT * FROM clients LIMIT 5 OFFSET 30 </sql> h3. Group @@ -747,6 +747,22 @@ h4. Specifying Conditions on Eager Loaded Associations Even though Active Record lets you specify conditions on the eager loaded associations just like +joins+, the recommended way is to use "joins":#joining-tables instead. +However if you must do this, you may use +where+ as you would normally. + +<ruby> +Post.includes(:comments).where("comments.visible", true) +</ruby> + +This would generate a query which contains a +LEFT OUTER JOIN+ whereas the +joins+ method would generate one using the +INNER JOIN+ function instead. + +<ruby> + SELECT "posts"."id" AS t0_r0, ... "comments"."updated_at" AS t1_r5 FROM "posts" LEFT OUTER JOIN "comments" ON "comments"."post_id" = "posts"."id" WHERE (comments.visible) +</ruby> + +If there was no +where+ condition, this would generate the normal set of two queries. + +If, in the case of this +includes+ query, there were no comments for any posts, all the posts would still be loaded. By using +joins+ (an INNER JOIN), the join conditions *must* match, otherwise no records will be returned. + h3. Scopes Scoping allows you to specify commonly-used ARel queries which can be referenced as method calls on the association objects or models. With these scopes, you can use every method previously covered such as +where+, +joins+ and +includes+. All scope methods will return an +ActiveRecord::Relation+ object which will allow for further methods (such as other scopes) to be called on it. |