Refactor `table_exists?` in AbstractMysqlAdapter

`table_exists?` calls `tables` twice when passed `'dbname.tblname'` arg.
This change is that `table_exists?` execute only once query always and
extra args of `tables` is removed.

3 files changed, 10 insertions, 27 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index 97f54dc0b0..feb41e96f0 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -625,33 +625,24 @@ module ActiveRecord
         show_variable 'collation_database'
       end
 
-      def tables(name = nil, database = nil, like = nil) #:nodoc:
-        sql = "SHOW TABLES "
-        sql << "IN #{quote_table_name(database)} " if database
-        sql << "LIKE #{quote(like)}" if like
-
-        execute_and_free(sql, 'SCHEMA') do |result|
-          result.collect(&:first)
-        end
+      def tables(name = nil) # :nodoc:
+        select_values("SHOW FULL TABLES", 'SCHEMA')
       end
 
       def truncate(table_name, name = nil)
         execute "TRUNCATE TABLE #{quote_table_name(table_name)}", name
       end
 
-      def table_exists?(name)
-        return false unless name.present?
-        return true if tables(nil, nil, name).any?
+      def table_exists?(table_name)
+        return false unless table_name.present?
 
-        name          = name.to_s
-        schema, table = name.split('.', 2)
+        schema, name = table_name.to_s.split('.', 2)
+        schema, name = @config[:database], schema unless name # A table was provided without a schema
 
-        unless table # A table was provided without a schema
-          table  = schema
-          schema = nil
-        end
+        sql = "SELECT table_name FROM information_schema.tables "
+        sql << "WHERE table_schema = #{quote(schema)} AND table_name = #{quote(name)}"
 
-        tables(nil, schema, table).any?
+        select_values(sql, 'SCHEMA').any?
       end
 
       def views # :nodoc:
diff --git a/activerecord/test/cases/adapters/mysql2/schema_test.rb b/activerecord/test/cases/adapters/mysql2/schema_test.rb
index 880a2123d2..faf2acb9cb 100644
--- a/activerecord/test/cases/adapters/mysql2/schema_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/schema_test.rb
@@ -36,14 +36,6 @@ module ActiveRecord
         assert(!@connection.table_exists?("#{@db_name}.zomg"), "table should not exist")
       end
 
-      def test_tables_quoting
-        @connection.tables(nil, "foo-bar", nil)
-        flunk
-      rescue => e
-        # assertion for *quoted* database properly
-        assert_match(/database 'foo-bar'/, e.inspect)
-      end
-
       def test_dump_indexes
         index_a_name = 'index_key_tests_on_snack'
         index_b_name = 'index_key_tests_on_pizza'
diff --git a/activerecord/test/cases/test_case.rb b/activerecord/test/cases/test_case.rb
index f93e85f5e2..47e664f4e7 100644
--- a/activerecord/test/cases/test_case.rb
+++ b/activerecord/test/cases/test_case.rb
@@ -103,7 +103,7 @@ module ActiveRecord
     # ignored SQL, or better yet, use a different notification for the queries
     # instead examining the SQL content.
     oracle_ignored     = [/^select .*nextval/i, /^SAVEPOINT/, /^ROLLBACK TO/, /^\s*select .* from all_triggers/im, /^\s*select .* from all_constraints/im, /^\s*select .* from all_tab_cols/im]
-    mysql_ignored      = [/^SHOW TABLES/i, /^SHOW FULL FIELDS/, /^SHOW CREATE TABLE /i, /^SHOW VARIABLES /, /^\s*SELECT column_name\b.*\bFROM information_schema\.key_column_usage\b/im]
+    mysql_ignored      = [/^SHOW FULL TABLES/i, /^SHOW FULL FIELDS/, /^SHOW CREATE TABLE /i, /^SHOW VARIABLES /, /^\s*SELECT (?:column_name|table_name)\b.*\bFROM information_schema\.(?:key_column_usage|tables)\b/im]
     postgresql_ignored = [/^\s*select\b.*\bfrom\b.*pg_namespace\b/im, /^\s*select tablename\b.*from pg_tables\b/im, /^\s*select\b.*\battname\b.*\bfrom\b.*\bpg_attribute\b/im, /^SHOW search_path/i]
     sqlite3_ignored =    [/^\s*SELECT name\b.*\bFROM sqlite_master/im, /^\s*SELECT sql\b.*\bFROM sqlite_master/im]