module ActiveRecord::ConnectionAdapters::DatabaseStatements
Constants
- DEFAULT_INSERT_VALUE
- TRANSACTION_ISOLATION_LEVELS
Public Class Methods
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 6 def initialize super reset_transaction end
Public Instance Methods
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 424 def add_transaction_record(record, ensure_finalize = true) current_transaction.add_record(record, ensure_finalize) end
Register a record with the current transaction so that its after_commit and after_rollback callbacks can be called.
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 429 def begin_db_transaction() end
Begins the transaction (and turns off auto-committing).
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 454 def begin_isolated_db_transaction(isolation) raise ActiveRecord::TransactionIsolationError, "adapter does not support setting transaction isolation" end
Begins the transaction with the isolation level set. Raises an error by default; adapters that support setting the isolation level should implement this method.
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 468 def commit_db_transaction() end
Commits the transaction (and turns on auto-committing).
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 490 def default_sequence_name(table, column) nil end
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 215 def delete(arel, name = nil, binds = []) sql, binds = to_sql_and_binds(arel, binds) exec_delete(sql, name, binds) end
Executes the delete statement and returns the number of rows affected.
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 520 def empty_insert_statement_value(primary_key = nil) "DEFAULT VALUES" end
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 168 def exec_delete(sql, name = nil, binds = []) affected_rows(internal_execute(sql, name, binds)) end
Executes delete sql statement in the context of this connection using binds as the bind substitutes. name is logged along with the executed sql statement.
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 160 def exec_insert(sql, name = nil, binds = [], pk = nil, sequence_name = nil, returning: nil) sql, binds = sql_for_insert(sql, pk, binds, returning) internal_exec_query(sql, name, binds) end
Executes insert sql statement in the context of this connection using binds as the bind substitutes. name is logged along with the executed sql statement. Some adapters support the ‘returning` keyword argument which allows to control the result of the query: `nil` is the default value and maintains default behavior. If an array of column names is passed - the result will contain values of the specified columns from the inserted row.
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 150 def exec_query(sql, name = "SQL", binds = [], prepare: false) internal_exec_query(sql, name, binds, prepare: prepare) end
Executes sql statement in the context of this connection using binds as the bind substitutes. name is logged along with the executed sql statement.
Note: the query is assumed to have side effects and the query cache will be cleared. If the query is read-only, consider using select_all instead.
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 175 def exec_update(sql, name = nil, binds = []) affected_rows(internal_execute(sql, name, binds)) end
Executes update sql statement in the context of this connection using binds as the bind substitutes. name is logged along with the executed sql statement.
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 139 def execute(sql, name = nil, allow_retry: false) internal_execute(sql, name, allow_retry: allow_retry) end
Executes the SQL statement in the context of this connection and returns the raw result from the connection adapter.
Setting allow_retry to true causes the db to reconnect and retry executing the SQL statement in case of a connection-related exception. This option should only be enabled for known idempotent queries.
Note: the query is assumed to have side effects and the query cache will be cleared. If the query is read-only, consider using select_all instead.
Note: depending on your database connector, the result returned by this method may be manually memory managed. Consider using exec_query wrapper instead.
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 544 def high_precision_current_timestamp HIGH_PRECISION_CURRENT_TIMESTAMP end
Returns an Arel SQL literal for the CURRENT_TIMESTAMP for usage with arbitrary precision date/time columns.
Adapters supporting datetime with precision should override this to provide as much precision as is available.
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 198 def insert(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = [], returning: nil) sql, binds = to_sql_and_binds(arel, binds) value = exec_insert(sql, name, binds, pk, sequence_name, returning: returning) return returning_column_values(value) unless returning.nil? id_value || last_inserted_id(value) end
Executes an INSERT query and returns the new record’s ID
id_value will be returned unless the value is nil, in which case the database will attempt to calculate the last inserted id and return that value.
If the next id was calculated in advance (as in Oracle), it should be passed in as id_value. Some adapters support the ‘returning` keyword argument which allows defining the return value of the method: `nil` is the default value and maintains default behavior. If an array of column names is passed - an array of is returned from the method representing values of the specified columns from the inserted row.
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 504 def insert_fixture(fixture, table_name) execute(build_fixture_sql(Array.wrap(fixture), table_name), "Fixture Insert") end
Inserts the given fixture into the table. Overridden in adapters that require something beyond a simple insert (e.g. Oracle). Most of adapters should implement insert_fixtures_set that leverages bulk SQL insert. We keep this method to provide fallback for databases like SQLite that do not support bulk inserts.
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 508 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)}" } statements = table_deletes + fixture_inserts transaction(requires_new: true) do disable_referential_integrity do execute_batch(statements, "Fixtures Load") end end end
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 464 def reset_isolation_level end
Hook point called after an isolated DB transaction is committed or rolled back. Most adapters don’t need to implement anything because the isolation level is set on a per transaction basis. But some databases like SQLite set it on a per connection level and need to explicitly reset it after commit or rollback.
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 495 def reset_sequence!(table, column, sequence = nil) # Do nothing by default. Implement for PostgreSQL, Oracle, ... end
Set the sequence to the max value of the table’s column.
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 480 def restart_db_transaction exec_restart_db_transaction end
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 472 def rollback_db_transaction exec_rollback_db_transaction rescue ActiveRecord::ConnectionNotEstablished, ActiveRecord::ConnectionFailed # Connection's gone; that counts as a rollback end
Rolls back the transaction (and turns on auto-committing). Must be done if the transaction block raises an exception or returns false.
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 486 def rollback_to_savepoint(name = nil) exec_rollback_to_savepoint(name) end
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 72 def select_all(arel, name = nil, binds = [], preparable: nil, async: false, allow_retry: false) arel = arel_from_relation(arel) sql, binds, preparable, allow_retry = to_sql_and_binds(arel, binds, preparable, allow_retry) select(sql, name, binds, prepare: prepared_statements && preparable, async: async && FutureResult::SelectAll, allow_retry: allow_retry ) rescue ::RangeError ActiveRecord::Result.empty(async: async) end
Returns an ActiveRecord::Result instance.
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 87 def select_one(arel, name = nil, binds = [], async: false) select_all(arel, name, binds, async: async).then(&:first) end
Returns a record hash with the column names as keys and column values as values.
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 104 def select_rows(arel, name = nil, binds = [], async: false) select_all(arel, name, binds, async: async).then(&:rows) end
Returns an array of arrays containing the field values. Order is the same as that returned by columns.
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 92 def select_value(arel, name = nil, binds = [], async: false) select_rows(arel, name, binds, async: async).then { |rows| single_value_from_rows(rows) } end
Returns a single value from a record
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 98 def select_values(arel, name = nil, binds = []) select_rows(arel, name, binds).map(&:first) end
Returns an array of the values of the first column in a select:
select_values("SELECT id FROM companies LIMIT 3") => [1,2,3]
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 12 def to_sql(arel_or_sql_string, binds = []) sql, _ = to_sql_and_binds(arel_or_sql_string, binds) sql end
Converts an arel AST to SQL
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 355 def transaction(requires_new: nil, isolation: nil, joinable: true, &block) # If we're running inside the single, non-joinable transaction that # ActiveRecord::TestFixtures starts around each example (depth == 1), # an `isolation:` hint must be validated then ignored so that the # adapter isn't asked to change the isolation level mid-transaction. if isolation && !requires_new && open_transactions == 1 && !current_transaction.joinable? iso = isolation.to_sym unless transaction_isolation_levels.include?(iso) raise ActiveRecord::TransactionIsolationError, "invalid transaction isolation level: #{iso.inspect}" end current_transaction.isolation = iso isolation = nil end if !requires_new && current_transaction.joinable? if isolation && current_transaction.isolation != isolation raise ActiveRecord::TransactionIsolationError, "cannot set isolation when joining a transaction" end yield current_transaction.user_transaction else within_new_transaction(isolation: isolation, joinable: joinable, &block) end rescue ActiveRecord::Rollback # rollbacks are silently swallowed end
Runs the given block in a database transaction, and returns the result of the block.
Transaction callbacks
transaction yields an ActiveRecord::Transaction object on which it is possible to register callback:
ActiveRecord::Base.transaction do |transaction| transaction.before_commit { puts "before commit!" } transaction.after_commit { puts "after commit!" } transaction.after_rollback { puts "after rollback!" } end
Nested transactions support
transaction calls can be nested. By default, this makes all database statements in the nested transaction block become part of the parent transaction. For example, the following behavior may be surprising:
ActiveRecord::Base.transaction do Post.create(title: 'first') ActiveRecord::Base.transaction do Post.create(title: 'second') raise ActiveRecord::Rollback end end
This creates both “first” and “second” posts. Reason is the ActiveRecord::Rollback exception in the nested block does not issue a ROLLBACK. Since these exceptions are captured in transaction blocks, the parent block does not see it and the real transaction is committed.
Most databases don’t support true nested transactions. At the time of writing, the only database that supports true nested transactions that we’re aware of, is MS-SQL.
In order to get around this problem, transaction will emulate the effect of nested transactions, by using savepoints: dev.mysql.com/doc/refman/en/savepoint.html.
It is safe to call this method if a database transaction is already open, i.e. if transaction is called within another transaction block. In case of a nested call, transaction will behave as follows:
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The block will be run without doing anything. All database statements that happen within the block are effectively appended to the already open database transaction.
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However, if
:requires_newis set, the block will be wrapped in a database savepoint acting as a sub-transaction.
In order to get a ROLLBACK for the nested transaction you may ask for a real sub-transaction by passing requires_new: true. If anything goes wrong, the database rolls back to the beginning of the sub-transaction without rolling back the parent transaction. If we add it to the previous example:
ActiveRecord::Base.transaction do Post.create(title: 'first') ActiveRecord::Base.transaction(requires_new: true) do Post.create(title: 'second') raise ActiveRecord::Rollback end end
only post with title “first” is created.
See ActiveRecord::Transactions to learn more.
Caveats
MySQL doesn’t support DDL transactions. If you perform a DDL operation, then any created savepoints will be automatically released. For example, if you’ve created a savepoint, then you execute a CREATE TABLE statement, then the savepoint that was created will be automatically released.
This means that, on MySQL, you shouldn’t execute DDL operations inside a transaction call that you know might create a savepoint. Otherwise, transaction will raise exceptions when it tries to release the already-automatically-released savepoints:
Model.lease_connection.transaction do # BEGIN
Model.lease_connection.transaction(requires_new: true) do # CREATE SAVEPOINT active_record_1
Model.lease_connection.create_table(...)
# active_record_1 now automatically released
end # RELEASE SAVEPOINT active_record_1 <--- BOOM! database error!
end
Transaction isolation
If your database supports setting the isolation level for a transaction, you can set it like so:
Post.transaction(isolation: :serializable) do # ... end
Valid isolation levels are:
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:read_uncommitted -
:read_committed -
:repeatable_read -
:serializable
You should consult the documentation for your database to understand the semantics of these different levels:
An ActiveRecord::TransactionIsolationError will be raised if:
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The adapter does not support setting the isolation level
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You are joining an existing open transaction
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You are creating a nested (savepoint) transaction
The mysql2, trilogy, and postgresql adapters support setting the transaction isolation level.
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 447 def transaction_isolation_levels TRANSACTION_ISOLATION_LEVELS end
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 398 def transaction_open? current_transaction.open? end
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 221 def truncate(table_name, name = nil) execute(build_truncate_statement(table_name), name) end
Executes the truncate statement.
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 209 def update(arel, name = nil, binds = []) sql, binds = to_sql_and_binds(arel, binds) exec_update(sql, name, binds) end
Executes the update statement and returns the number of rows affected.
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 121 def write_query?(sql) raise NotImplementedError end
Determines whether the SQL statement is a write query.
Private Instance Methods
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 590 def affected_rows(raw_result) raise NotImplementedError end
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 747 def arel_from_relation(relation) if relation.is_a?(Relation) relation.arel else relation end end
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 622 def build_fixture_sql(fixtures, table_name) columns = schema_cache.columns_hash(table_name).reject { |_, column| supports_virtual_columns? && column.virtual? } values_list = fixtures.map do |fixture| fixture = fixture.stringify_keys unknown_columns = fixture.keys - columns.keys if unknown_columns.any? raise Fixture::FixtureError, %(table "#{table_name}" has no columns named #{unknown_columns.map(&:inspect).join(', ')}.) end columns.map do |name, column| if fixture.key?(name) # TODO: Remove fetch_cast_type and the need for connection after we release 8.1. with_yaml_fallback(column.fetch_cast_type(self).serialize(fixture[name])) else default_insert_value(column) end end end table = Arel::Table.new(table_name) manager = Arel::InsertManager.new(table) if values_list.size == 1 values = values_list.shift new_values = [] columns.each_key.with_index { |column, i| unless values[i].equal?(DEFAULT_INSERT_VALUE) new_values << values[i] manager.columns << table[column] end } values_list << new_values else columns.each_key { |column| manager.columns << table[column] } end manager.values = manager.create_values_list(values_list) visitor.compile(manager.ast) end
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 664 def build_fixture_statements(fixture_set) fixture_set.filter_map do |table_name, fixtures| next if fixtures.empty? build_fixture_sql(fixtures, table_name) end end
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 671 def build_truncate_statement(table_name) "TRUNCATE TABLE #{quote_table_name(table_name)}" end
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 675 def build_truncate_statements(table_names) table_names.map do |table_name| build_truncate_statement(table_name) end end
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 586 def cast_result(raw_result) raise NotImplementedError end
Receive a native adapter result object and returns an ActiveRecord::Result object.
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 681 def combine_multi_statements(total_sql) total_sql.join(";\n") end
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 616 def execute_batch(statements, name = nil, **kwargs) statements.each do |statement| raw_execute(statement, name, **kwargs) end end
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 755 def extract_table_ref_from_insert_sql(sql) if sql =~ /into\s("[A-Za-z0-9_."\[\]\s]+"|[A-Za-z0-9_."\[\]]+)\s*/im $1.delete('"').strip end end
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 582 def handle_warnings(raw_result, sql) end
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 611 def internal_execute(sql, name = "SQL", binds = [], prepare: false, async: false, allow_retry: false, materialize_transactions: true, &block) sql = preprocess_query(sql) raw_execute(sql, name, binds, prepare: prepare, async: async, allow_retry: allow_retry, materialize_transactions: materialize_transactions, &block) end
Same as internal_exec_query, but yields a native adapter result
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 734 def last_inserted_id(result) single_value_from_rows(result.rows) end
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 578 def perform_query(raw_connection, sql, binds, type_casted_binds, prepare:, notification_payload:, batch:) raise NotImplementedError end
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 594 def preprocess_query(sql) if write_query?(sql) ensure_writes_are_allowed(sql) mark_transaction_written end # We call tranformers after the write checks so we don't add extra parsing work. # This means we assume no transformer whille change a read for a write # but it would be insane to do such a thing. ActiveRecord.query_transformers.each do |transformer| sql = transformer.call(sql, self) end sql end
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 567 def raw_execute(sql, name = nil, binds = [], prepare: false, async: false, allow_retry: false, materialize_transactions: true, batch: false) type_casted_binds = type_casted_binds(binds) log(sql, name, binds, type_casted_binds, async: async, allow_retry: allow_retry) do |notification_payload| with_raw_connection(allow_retry: allow_retry, materialize_transactions: materialize_transactions) do |conn| result = perform_query(conn, sql, binds, type_casted_binds, prepare: prepare, notification_payload: notification_payload, batch: batch) handle_warnings(result, sql) result end end end
Lowest level way to execute a query. Doesn’t check for illegal writes, doesn’t annotate queries, yields a native result object.
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 738 def returning_column_values(result) [last_inserted_id(result)] end
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 686 def select(sql, name = nil, binds = [], prepare: false, async: false, allow_retry: false) if async && async_enabled? if current_transaction.joinable? raise AsynchronousQueryInsideTransactionError, "Asynchronous queries are not allowed inside transactions" end # We make sure to run query transformers on the original thread sql = preprocess_query(sql) future_result = async.new( pool, sql, name, binds, prepare: prepare, ) if supports_concurrent_connections? && !current_transaction.joinable? future_result.schedule!(ActiveRecord::Base.asynchronous_queries_session) else future_result.execute!(self) end future_result else result = internal_exec_query(sql, name, binds, prepare: prepare, allow_retry: allow_retry) if async FutureResult.wrap(result) else result end end end
Returns an ActiveRecord::Result instance.
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# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 742 def single_value_from_rows(rows) row = rows.first row && row.first end