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| author | Ryan Bigg <radarlistener@gmail.com> | 2011-03-22 12:16:15 +1100 |
|---|---|---|
| committer | Ryan Bigg <radarlistener@gmail.com> | 2011-03-22 12:16:15 +1100 |
| commit | 5a44951186b410c3a79685f8aeaa926d93a6aab0 (patch) | |
| tree | be5394145590a884c690c064518b02372b328a83 /railties/guides | |
| parent | c24e5548fd372e4d0058ab417230ebc2fa3bebde (diff) | |
| download | rails-5a44951186b410c3a79685f8aeaa926d93a6aab0.tar.gz rails-5a44951186b410c3a79685f8aeaa926d93a6aab0.tar.bz2 rails-5a44951186b410c3a79685f8aeaa926d93a6aab0.zip | |
Querying guide: mention that performing a where on an relation that contains an includes statement will generate a LEFT OUTER JOIN rather than an INNER JOIN or another query
Diffstat (limited to 'railties/guides')
| -rw-r--r-- | railties/guides/source/active_record_querying.textile | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/railties/guides/source/active_record_querying.textile b/railties/guides/source/active_record_querying.textile index e0fab46db9..009d541106 100644 --- a/railties/guides/source/active_record_querying.textile +++ b/railties/guides/source/active_record_querying.textile @@ -759,7 +759,9 @@ This would generate a query which contains a +LEFT OUTER JOIN+ whereas the +join 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 in this case 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. +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 |