diff options
Diffstat (limited to 'activerecord/lib/active_record/connection_adapters/mysql_adapter.rb')
| -rw-r--r-- | activerecord/lib/active_record/connection_adapters/mysql_adapter.rb | 25 |
1 files changed, 25 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb index 9e6cb13cca..a44ac08ce4 100644 --- a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb +++ b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb @@ -192,6 +192,10 @@ module ActiveRecord connect end + def self.visitor_for(pool) # :nodoc: + Arel::Visitors::MySQL.new(pool) + end + def adapter_name #:nodoc: ADAPTER_NAME end @@ -487,6 +491,27 @@ module ActiveRecord execute("RELEASE SAVEPOINT #{current_savepoint_name}") end + # In the simple case, MySQL allows us to place JOINs directly into the UPDATE + # query. However, this does not allow for LIMIT, OFFSET and ORDER. To support + # these, we must use a subquery. However, MySQL is too stupid to create a + # temporary table for this automatically, so we have to give it some prompting + # in the form of a subsubquery. Ugh! + def join_to_update(update, select) #:nodoc: + if select.limit || select.offset || select.orders.any? + subsubselect = select.clone + subsubselect.projections = [update.key] + + subselect = Arel::SelectManager.new(select.engine) + subselect.project Arel.sql(update.key.name) + subselect.from subsubselect.as('__active_record_temp') + + update.where update.key.in(subselect) + else + update.table select.source + update.wheres = select.constraints + end + end + # SCHEMA STATEMENTS ======================================== def structure_dump #:nodoc: |