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 349 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 354 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 368 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 373 def commit_db_transaction() end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 387 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 183 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 419 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 142 def exec_delete(sql, name = nil, binds = []) 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.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 134 def exec_insert(sql, name = nil, binds = [], pk = nil, sequence_name = nil) sql, binds = sql_for_insert(sql, pk, binds) 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.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 127 def exec_query(sql, name = "SQL", binds = [], prepare: false) raise NotImplementedError 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 149 def exec_update(sql, name = nil, binds = []) exec_query(sql, name, binds) end
Executes the SQL statement in the context of this connection and returns the raw result from the connection adapter. Note: depending on your database connector, the result returned by this method may be manually memory managed. Consider using the exec_query
wrapper instead.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 120 def execute(sql, name = nil) raise NotImplementedError 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
.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 169 def insert(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = []) sql, binds = to_sql_and_binds(arel, binds) value = exec_insert(sql, name, binds, pk, sequence_name) 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 401 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 405 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 with_multi_statements do disable_referential_integrity do transaction(requires_new: true) do execute_batch(statements, "Fixtures Load") end end end end
Set the sequence to the max value of the table's column.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 392 def reset_sequence!(table, column, sequence = nil) # Do nothing by default. Implement for PostgreSQL, Oracle, ... 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 377 def rollback_db_transaction exec_rollback_db_transaction end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 383 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 429 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 62 def select_all(arel, name = nil, binds = [], preparable: nil) arel = arel_from_relation(arel) sql, binds, preparable = to_sql_and_binds(arel, binds, preparable) if prepared_statements && preparable select_prepared(sql, name, binds) else select(sql, name, binds) end rescue ::RangeError ActiveRecord::Result.new([], []) 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 77 def select_one(arel, name = nil, binds = []) select_all(arel, name, binds).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 94 def select_rows(arel, name = nil, binds = []) select_all(arel, name, binds).rows end
Returns a single value from a record
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 82 def select_value(arel, name = nil, binds = []) single_value_from_rows(select_rows(arel, name, binds)) 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 88 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.
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.connection.transaction do # BEGIN Model.connection.transaction(requires_new: true) do # CREATE SAVEPOINT active_record_1 Model.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 and postgresql adapters support setting the transaction isolation level.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 313 def transaction(requires_new: nil, isolation: nil, joinable: true) if !requires_new && current_transaction.joinable? if isolation raise ActiveRecord::TransactionIsolationError, "cannot set isolation when joining a transaction" end yield else transaction_manager.within_new_transaction(isolation: isolation, joinable: joinable) { yield } end rescue ActiveRecord::Rollback # rollbacks are silently swallowed end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 356 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 339 def transaction_open? current_transaction.open? end
Executes the truncate statement.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 189 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 177 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 111 def write_query?(sql) raise NotImplementedError end
Private Instance Methods
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 552 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 462 def build_fixture_sql(fixtures, table_name) columns = schema_cache.columns_hash(table_name) 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 manager.into(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 505 def build_fixture_statements(fixture_set) fixture_set.map do |table_name, fixtures| next if fixtures.empty? build_fixture_sql(fixtures, table_name) end.compact end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 512 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 516 def build_truncate_statements(table_names) table_names.map do |table_name| build_truncate_statement(table_name) end end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 526 def combine_multi_statements(total_sql) total_sql.join(";\n") end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 458 def default_insert_value(column) DEFAULT_INSERT_VALUE end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 449 def execute_batch(statements, name = nil) statements.each do |statement| execute(statement, name) end end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 543 def last_inserted_id(result) single_value_from_rows(result.rows) end
Returns an ActiveRecord::Result
instance.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 531 def select(sql, name = nil, binds = []) exec_query(sql, name, binds, prepare: false) end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 535 def select_prepared(sql, name = nil, binds = []) exec_query(sql, name, binds, prepare: true) end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 547 def single_value_from_rows(rows) row = rows.first row && row.first end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 539 def sql_for_insert(sql, pk, binds) [sql, binds] end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 522 def with_multi_statements yield end