module ActiveRecord::ConnectionAdapters::DatabaseStatements
Constants
- DEFAULT_INSERT_VALUE
Public Class Methods
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 6 def initialize super reset_transaction end
Public Instance Methods
Register a record with the current transaction so that its after_commit and after_rollback callbacks can be called.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 405 def add_transaction_record(record, ensure_finalize = true) current_transaction.add_record(record, ensure_finalize) end
Begins the transaction (and turns off auto-committing).
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 410 def begin_db_transaction() 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.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 432 def begin_isolated_db_transaction(isolation) raise ActiveRecord::TransactionIsolationError, "adapter does not support setting transaction isolation" end
Commits the transaction (and turns on auto-committing).
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 446 def commit_db_transaction() end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 468 def default_sequence_name(table, column) nil end
Executes the delete statement and returns the number of rows affected.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 212 def delete(arel, name = nil, binds = []) sql, binds = to_sql_and_binds(arel, binds) exec_delete(sql, name, binds) end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 498 def empty_insert_statement_value(primary_key = nil) "DEFAULT VALUES" 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.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 165 def exec_delete(sql, name = nil, binds = []) affected_rows(internal_execute(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.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 157 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 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.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 147 def exec_query(sql, name = "SQL", binds = [], prepare: false) internal_exec_query(sql, name, binds, prepare: prepare) 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.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 172 def exec_update(sql, name = nil, binds = []) affected_rows(internal_execute(sql, name, binds)) 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.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 136 def execute(sql, name = nil, allow_retry: false) internal_execute(sql, name, allow_retry: allow_retry) 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.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 536 def high_precision_current_timestamp HIGH_PRECISION_CURRENT_TIMESTAMP 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.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 195 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
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.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 482 def insert_fixture(fixture, table_name) execute(build_fixture_sql(Array.wrap(fixture), table_name), "Fixture Insert") end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 486 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
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.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 442 def reset_isolation_level end
Set the sequence to the max value of the table’s column.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 473 def reset_sequence!(table, column, sequence = nil) # Do nothing by default. Implement for PostgreSQL, Oracle, ... end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 458 def restart_db_transaction exec_restart_db_transaction end
Rolls back the transaction (and turns on auto-committing). Must be done if the transaction block raises an exception or returns false.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 450 def rollback_db_transaction exec_rollback_db_transaction rescue ActiveRecord::ConnectionNotEstablished, ActiveRecord::ConnectionFailed # Connection's gone; that counts as a rollback end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 464 def rollback_to_savepoint(name = nil) exec_rollback_to_savepoint(name) end
Sanitizes the given LIMIT parameter in order to prevent SQL injection.
The limit
may be anything that can evaluate to a string via to_s. It should look like an integer, or an Arel
SQL literal.
Returns Integer and Arel::Nodes::SqlLiteral limits as is.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 508 def sanitize_limit(limit) if limit.is_a?(Integer) || limit.is_a?(Arel::Nodes::SqlLiteral) limit else Integer(limit) end end
Returns an ActiveRecord::Result
instance.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 69 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 a record hash with the column names as keys and column values as values.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 84 def select_one(arel, name = nil, binds = [], async: false) select_all(arel, name, binds, async: async).then(&:first) end
Returns an array of arrays containing the field values. Order is the same as that returned by columns
.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 101 def select_rows(arel, name = nil, binds = [], async: false) select_all(arel, name, binds, async: async).then(&:rows) end
Returns a single value from a record
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 89 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 an array of the values of the first column in a select:
select_values("SELECT id FROM companies LIMIT 3") => [1,2,3]
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 95 def select_values(arel, name = nil, binds = []) select_rows(arel, name, binds).map(&:first) end
Converts an arel AST to SQL
# 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
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:
-
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.
-
However, if
:requires_new
is 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:
-
: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:
-
The adapter does not support setting the isolation level
-
You are joining an existing open transaction
-
You are creating a nested (savepoint) transaction
The mysql2, trilogy, and postgresql adapters support setting the transaction isolation level.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 352 def transaction(requires_new: nil, isolation: nil, joinable: true, &block) if !requires_new && current_transaction.joinable? if 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
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 420 def transaction_isolation_levels { read_uncommitted: "READ UNCOMMITTED", read_committed: "READ COMMITTED", repeatable_read: "REPEATABLE READ", serializable: "SERIALIZABLE" } end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 379 def transaction_open? current_transaction.open? end
Executes the truncate statement.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 218 def truncate(table_name, name = nil) execute(build_truncate_statement(table_name), name) end
Executes the update statement and returns the number of rows affected.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 206 def update(arel, name = nil, binds = []) sql, binds = to_sql_and_binds(arel, binds) exec_update(sql, name, binds) end
Determines whether the SQL statement is a write query.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 118 def write_query?(sql) raise NotImplementedError end
Private Instance Methods
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 570 def affected_rows(raw_result) raise NotImplementedError end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 732 def arel_from_relation(relation) if relation.is_a?(Relation) relation.arel else relation end end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 607 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) type = lookup_cast_type_from_column(column) with_yaml_fallback(type.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
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 649 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
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 656 def build_truncate_statement(table_name) "TRUNCATE TABLE #{quote_table_name(table_name)}" end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 660 def build_truncate_statements(table_names) table_names.map do |table_name| build_truncate_statement(table_name) end end
Receive a native adapter result object and returns an ActiveRecord::Result
object.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 566 def cast_result(raw_result) raise NotImplementedError end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 666 def combine_multi_statements(total_sql) total_sql.join(";\n") end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 603 def default_insert_value(column) DEFAULT_INSERT_VALUE end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 594 def execute_batch(statements, name = nil, **kwargs) statements.each do |statement| raw_execute(statement, name, **kwargs) end end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 740 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
Same as internal_exec_query, but yields a native adapter result
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 589 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
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 719 def last_inserted_id(result) single_value_from_rows(result.rows) end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 561 def perform_query(raw_connection, sql, binds, type_casted_binds, prepare:, notification_payload:, batch:) raise NotImplementedError end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 574 def preprocess_query(sql) check_if_write_query(sql) mark_transaction_written_if_write(sql) # 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
Lowest level way to execute a query. Doesn’t check for illegal writes, doesn’t annotate queries, yields a native result object.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 552 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) do |notification_payload| with_raw_connection(allow_retry: allow_retry, materialize_transactions: materialize_transactions) do |conn| perform_query(conn, sql, binds, type_casted_binds, prepare: prepare, notification_payload: notification_payload, batch: batch) end end end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 723 def returning_column_values(result) [last_inserted_id(result)] end
Returns an ActiveRecord::Result
instance.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 671 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
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 727 def single_value_from_rows(rows) row = rows.first row && row.first end