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rails / 7.0 / activerecord / connectionadapters / databasestatements.html

module ActiveRecord::ConnectionAdapters::DatabaseStatements

Public Class Methods

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 6
def initialize
  super
  reset_transaction
end
Calls superclass method

Public Instance Methods

add_transaction_record(record, ensure_finalize = true) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 345
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.

begin_db_transaction() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 350
def begin_db_transaction()    end

Begins the transaction (and turns off auto-committing).

begin_isolated_db_transaction(isolation) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 364
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.

commit_db_transaction() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 369
def commit_db_transaction()   end

Commits the transaction (and turns on auto-committing).

create(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = [])
Alias for: insert
default_sequence_name(table, column) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 383
def default_sequence_name(table, column)
  nil
end
delete(arel, name = nil, binds = []) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 179
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.

empty_insert_statement_value(primary_key = nil) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 415
def empty_insert_statement_value(primary_key = nil)
  "DEFAULT VALUES"
end
exec_delete(sql, name = nil, binds = []) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 138
def exec_delete(sql, name = nil, binds = [])
  exec_query(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.

exec_insert(sql, name = nil, binds = [], pk = nil, sequence_name = nil) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 130
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 insert sql statement in the context of this connection using binds as the bind substitutes. name is logged along with the executed sql statement.

exec_query(sql, name = "SQL", binds = [], prepare: false) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 123
def exec_query(sql, name = "SQL", binds = [], prepare: false)
  raise NotImplementedError
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.

exec_update(sql, name = nil, binds = []) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 145
def exec_update(sql, name = nil, binds = [])
  exec_query(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.

execute(sql, name = nil) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 116
def execute(sql, name = nil)
  raise NotImplementedError
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.

high_precision_current_timestamp() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 453
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.

insert(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = []) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 165
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

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.

Also aliased as: create
insert_fixture(fixture, table_name) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 397
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.

insert_fixtures_set(fixture_set, tables_to_delete = []) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 401
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
reset_sequence!(table, column, sequence = nil) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 388
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.

rollback_db_transaction() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 373
def rollback_db_transaction
  exec_rollback_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.

rollback_to_savepoint(name = nil) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 379
def rollback_to_savepoint(name = nil)
  exec_rollback_to_savepoint(name)
end
sanitize_limit(limit) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 425
def sanitize_limit(limit)
  if limit.is_a?(Integer) || limit.is_a?(Arel::Nodes::SqlLiteral)
    limit
  else
    Integer(limit)
  end
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.

select_all(arel, name = nil, binds = [], preparable: nil, async: false) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 62
def select_all(arel, name = nil, binds = [], preparable: nil, async: false)
  arel = arel_from_relation(arel)
  sql, binds, preparable = to_sql_and_binds(arel, binds, preparable)

  select(sql, name, binds, prepare: prepared_statements && preparable, async: async && FutureResult::SelectAll)
rescue ::RangeError
  ActiveRecord::Result.empty
end

Returns an ActiveRecord::Result instance.

select_one(arel, name = nil, binds = []) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 73
def select_one(arel, name = nil, binds = [])
  select_all(arel, name, binds).first
end

Returns a record hash with the column names as keys and column values as values.

select_rows(arel, name = nil, binds = []) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 90
def select_rows(arel, name = nil, binds = [])
  select_all(arel, name, binds).rows
end

Returns an array of arrays containing the field values. Order is the same as that returned by columns.

select_value(arel, name = nil, binds = []) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 78
def select_value(arel, name = nil, binds = [])
  single_value_from_rows(select_rows(arel, name, binds))
end

Returns a single value from a record

select_values(arel, name = nil, binds = []) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 84
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]
to_sql(arel_or_sql_string, binds = []) Show source 
# File activerecord/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

transaction(requires_new: nil, isolation: nil, joinable: true) { || ... } Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 309
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
  else
    transaction_manager.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.

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.

transaction_isolation_levels() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 352
def transaction_isolation_levels
  {
    read_uncommitted: "READ UNCOMMITTED",
    read_committed:   "READ COMMITTED",
    repeatable_read:  "REPEATABLE READ",
    serializable:     "SERIALIZABLE"
  }
end
transaction_open?() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 335
def transaction_open?
  current_transaction.open?
end
truncate(table_name, name = nil) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 185
def truncate(table_name, name = nil)
  execute(build_truncate_statement(table_name), name)
end

Executes the truncate statement.

update(arel, name = nil, binds = []) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 173
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.

write_query?(sql) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 107
def write_query?(sql)
  raise NotImplementedError
end

Determines whether the SQL statement is a write query.

© 2004–2021 David Heinemeier Hansson
Licensed under the MIT License.