diff options
Diffstat (limited to 'activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb')
-rw-r--r-- | activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb | 44 |
1 files changed, 43 insertions, 1 deletions
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb index 15e329a1c8..44c2fa439c 100644 --- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb +++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb @@ -517,6 +517,48 @@ module ActiveRecord # DATABASE STATEMENTS ====================================== + def explain(arel) + sql = "EXPLAIN #{to_sql(arel)}" + ExplainPrettyPrinter.new.pp(exec_query(sql)) + end + + class ExplainPrettyPrinter # :nodoc: + # Pretty prints the result of a EXPLAIN in a way that resembles the output of the + # PostgreSQL shell: + # + # QUERY PLAN + # ------------------------------------------------------------------------------ + # Nested Loop Left Join (cost=0.00..37.24 rows=8 width=0) + # Join Filter: (posts.user_id = users.id) + # -> Index Scan using users_pkey on users (cost=0.00..8.27 rows=1 width=4) + # Index Cond: (id = 1) + # -> Seq Scan on posts (cost=0.00..28.88 rows=8 width=4) + # Filter: (posts.user_id = 1) + # (6 rows) + # + def pp(result) + header = result.columns.first + lines = result.rows.map(&:first) + + # We add 2 because there's one char of padding at both sides, note + # the extra hyphens in the example above. + width = [header, *lines].map(&:length).max + 2 + + pp = [] + + pp << header.center(width).rstrip + pp << '-' * width + + pp += lines.map {|line| " #{line}"} + + nrows = result.rows.length + rows_label = nrows == 1 ? 'row' : 'rows' + pp << "(#{nrows} #{rows_label})" + + pp.join("\n") + "\n" + end + end + # Executes a SELECT query and returns an array of rows. Each row is an # array of field values. def select_rows(sql, name = nil) @@ -836,7 +878,7 @@ module ActiveRecord # Returns the active schema search path. def schema_search_path - @schema_search_path ||= query('SHOW search_path')[0][0] + @schema_search_path ||= query('SHOW search_path', 'SCHEMA')[0][0] end # Returns the current client message level. |