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| author | Ryuta Kamizono <kamipo@gmail.com> | 2016-11-07 00:27:50 +0900 |
|---|---|---|
| committer | Ryuta Kamizono <kamipo@gmail.com> | 2016-11-09 18:47:39 +0900 |
| commit | 2bf7c30049558c2503f20e9810fdf4727650fe99 (patch) | |
| tree | 27f7aebb843c001060d6d1b39bd97d443f23ef43 /activerecord | |
| parent | 1b16e4c348055e9e7909e59e47dbe346b149ba52 (diff) | |
| download | rails-2bf7c30049558c2503f20e9810fdf4727650fe99.tar.gz rails-2bf7c30049558c2503f20e9810fdf4727650fe99.tar.bz2 rails-2bf7c30049558c2503f20e9810fdf4727650fe99.zip | |
Should except `:distinct` rather than `:order` for `exists?`
Records fetching order is very important for performance if `limit` is
presented. Should not except the order in the case.
And `exists?` replaces select list to `1 AS one` therefore `:distinct`
is useless (`DISTINCT 1 AS one`). And PostgreSQL raises the following
error if `:distinct` and `:order` are used in the same time.
```
ERROR: for SELECT DISTINCT, ORDER BY expressions must appear in select list
```
Diffstat (limited to 'activerecord')
| -rw-r--r-- | activerecord/CHANGELOG.md | 3 | ||||
| -rw-r--r-- | activerecord/lib/active_record/relation/finder_methods.rb | 2 |
2 files changed, 3 insertions, 2 deletions
diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md index dd2a1b4b19..a85fa321cd 100644 --- a/activerecord/CHANGELOG.md +++ b/activerecord/CHANGELOG.md @@ -7,7 +7,8 @@ *Pavel Evstigneev* -* Avoid `unscope(:order)` when `limit_value` is presented for `count`. +* Avoid `unscope(:order)` when `limit_value` is presented for `count` + and `exists?`. If `limit_value` is presented, records fetching order is very important for performance. Should not unscope the order in the case. diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb index 97a819c5af..55ded4c6d0 100644 --- a/activerecord/lib/active_record/relation/finder_methods.rb +++ b/activerecord/lib/active_record/relation/finder_methods.rb @@ -321,7 +321,7 @@ module ActiveRecord relation = apply_join_dependency(self, construct_join_dependency(eager_loading: false)) return false if ActiveRecord::NullRelation === relation - relation = relation.except(:select, :order).select(ONE_AS_ONE).limit(1) + relation = relation.except(:select, :distinct).select(ONE_AS_ONE).limit(1) case conditions when Array, Hash |