Change execute_batch to take array of statements

Adapters don't necessarily have the ability to execute a batch of
statements.

Previously execute_batch took a single string of statements separated by
';', this meant that the adapter had to have the ability to execute
batch statements.

Instead, this commit changes the method to take an array of statements.
Adapters which support batched queries can do the join there. For
adapters which don't we provide a fallback implementation: executing
each statement one at a time.

This also improves the implementation for the mysql2 adapter, which
understands that there is a maximium query length. Previously the caller
needed to split the statements before passing them to execute_batch, now
execute_batch itself is responsible for splitting the queries.

activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb

@@ -184,7 +184,7 @@ def delete(arel, name = nil, binds = [])
 
       # Executes the truncate statement.
       def truncate(table_name, name = nil)
-        execute(build_truncate_statements(table_name), name)
+        execute(build_truncate_statement(table_name), name)
       end
 
       def truncate_tables(*table_names) # :nodoc:
@@ -194,9 +194,8 @@ def truncate_tables(*table_names) # :nodoc:
 
         with_multi_statements do
           disable_referential_integrity do
-            Array(build_truncate_statements(*table_names)).each do |sql|
-              execute_batch(sql, "Truncate Tables")
-            end
+            statements = build_truncate_statements(table_names)
+            execute_batch(statements, "Truncate Tables")
           end
         end
       end
@@ -365,14 +364,12 @@ def insert_fixture(fixture, table_name)
       def insert_fixtures_set(fixture_set, tables_to_delete = [])
         fixture_inserts = build_fixture_statements(fixture_set)
         table_deletes = tables_to_delete.map { |table| "DELETE FROM #{quote_table_name(table)}" }
-        total_sql = Array(combine_multi_statements(table_deletes + fixture_inserts))
+        statements = table_deletes + fixture_inserts
 
         with_multi_statements do
           disable_referential_integrity do
             transaction(requires_new: true) do
-              total_sql.each do |sql|
-                execute_batch(sql, "Fixtures Load")
-              end
+              execute_batch(statements, "Fixtures Load")
             end
           end
         end
@@ -408,8 +405,10 @@ def with_yaml_fallback(value) # :nodoc:
       end
 
       private
-        def execute_batch(sql, name = nil)
-          execute(sql, name)
+        def execute_batch(statements, name = nil)
+          statements.each do |statement|
+            execute(statement, name)
+          end
         end
 
         DEFAULT_INSERT_VALUE = Arel.sql("DEFAULT").freeze
@@ -469,11 +468,14 @@ def build_fixture_statements(fixture_set)
           end.compact
         end
 
-        def build_truncate_statements(*table_names)
-          truncate_tables = table_names.map do |table_name|
-            "TRUNCATE TABLE #{quote_table_name(table_name)}"
+        def build_truncate_statement(table_name)
+          "TRUNCATE TABLE #{quote_table_name(table_name)}"
+        end
+
+        def build_truncate_statements(table_names)
+          table_names.map do |table_name|
+            build_truncate_statement(table_name)
           end
-          combine_multi_statements(truncate_tables)
         end
 
         def with_multi_statements

activerecord/lib/active_record/connection_adapters/mysql/database_statements.rb

@@ -82,8 +82,10 @@ def exec_delete(sql, name = nil, binds = [])
         alias :exec_update :exec_delete
 
         private
-          def execute_batch(sql, name = nil)
-            super
+          def execute_batch(statements, name = nil)
+            combine_multi_statements(statements).each do |statement|
+              execute(statement, name)
+            end
             @connection.abandon_results!
           end
 
@@ -99,14 +101,6 @@ def supports_set_server_option?
             @connection.respond_to?(:set_server_option)
           end
 
-          def build_truncate_statements(*table_names)
-            if table_names.size == 1
-              super.first
-            else
-              super
-            end
-          end
-
           def multi_statements_enabled?(flags)
             if flags.is_a?(Array)
               flags.include?("MULTI_STATEMENTS")

activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb

@@ -166,8 +166,12 @@ def exec_rollback_db_transaction
         end
 
         private
-          def build_truncate_statements(*table_names)
-            "TRUNCATE TABLE #{table_names.map(&method(:quote_table_name)).join(", ")}"
+          def execute_batch(statements, name = nil)
+            execute(combine_multi_statements(statements))
+          end
+
+          def build_truncate_statements(table_names)
+            ["TRUNCATE TABLE #{table_names.map(&method(:quote_table_name)).join(", ")}"]
           end
 
           # Returns the current ID of a table's sequence.

activerecord/lib/active_record/connection_adapters/sqlite3/database_statements.rb

@@ -87,7 +87,9 @@ def exec_rollback_db_transaction #:nodoc:
         end
 
         private
-          def execute_batch(sql, name = nil)
+          def execute_batch(statements, name = nil)
+            sql = combine_multi_statements(statements)
+
             if preventing_writes? && write_query?(sql)
               raise ActiveRecord::ReadOnlyError, "Write query attempted while in readonly mode: #{sql}"
             end
@@ -112,11 +114,8 @@ def build_fixture_statements(fixture_set)
             end.compact
           end
 
-          def build_truncate_statements(*table_names)
-            truncate_tables = table_names.map do |table_name|
-              "DELETE FROM #{quote_table_name(table_name)}"
-            end
-            combine_multi_statements(truncate_tables)
+          def build_truncate_statement(table_name)
+            "DELETE FROM #{quote_table_name(table_name)}"
           end
       end
     end