module ActiveRecord::ConnectionAdapters::DatabaseStatements

Constants

DEFAULT_INSERT_VALUE

Public Class Methods

new() click to toggle source
Calls superclass method
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 6
def initialize
  super
  reset_transaction
end

Public Instance Methods

add_transaction_record(record, ensure_finalize = true) click to toggle source

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
begin_db_transaction() click to toggle source

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
begin_isolated_db_transaction(isolation) click to toggle source

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
commit_db_transaction() click to toggle source

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
create(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = [])
Alias for: insert
default_sequence_name(table, column) click to toggle source
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 387
def default_sequence_name(table, column)
  nil
end
delete(arel, name = nil, binds = []) click to toggle source

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
empty_insert_statement_value(primary_key = nil) click to toggle source
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 419
def empty_insert_statement_value(primary_key = nil)
  "DEFAULT VALUES"
end
exec_delete(sql, name = nil, binds = []) click to toggle source

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
exec_insert(sql, name = nil, binds = [], pk = nil, sequence_name = nil) click to toggle source

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
exec_query(sql, name = "SQL", binds = [], prepare: false) click to toggle source

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
exec_update(sql, name = nil, binds = []) click to toggle source

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
execute(sql, name = nil) click to toggle source

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
insert(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = []) click to toggle source

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
Also aliased as: create
insert_fixture(fixture, table_name) click to toggle source

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
insert_fixtures_set(fixture_set, tables_to_delete = []) click to toggle source
# 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
reset_sequence!(table, column, sequence = nil) click to toggle source

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
rollback_db_transaction() click to toggle source

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
rollback_to_savepoint(name = nil) click to toggle source
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 383
def rollback_to_savepoint(name = nil)
  exec_rollback_to_savepoint(name)
end
sanitize_limit(limit) click to toggle source

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
select_all(arel, name = nil, binds = [], preparable: nil) click to toggle source

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
select_one(arel, name = nil, binds = []) click to toggle source

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
select_rows(arel, name = nil, binds = []) click to toggle source

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
select_value(arel, name = nil, binds = []) click to toggle source

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
select_values(arel, name = nil, binds = []) click to toggle source

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
to_sql(arel_or_sql_string, binds = []) click to toggle source

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
transaction(requires_new: nil, isolation: nil, joinable: true) { || ... } click to toggle source

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
transaction_isolation_levels() click to toggle source
# 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
transaction_open?() click to toggle source
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 339
def transaction_open?
  current_transaction.open?
end
truncate(table_name, name = nil) click to toggle source

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
update(arel, name = nil, binds = []) click to toggle source

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
write_query?(sql) click to toggle source

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

arel_from_relation(relation) click to toggle source
# 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
build_fixture_sql(fixtures, table_name) click to toggle source
# 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
build_fixture_statements(fixture_set) click to toggle source
# 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
build_truncate_statement(table_name) click to toggle source
# 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
build_truncate_statements(table_names) click to toggle source
# 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
combine_multi_statements(total_sql) click to toggle source
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 526
def combine_multi_statements(total_sql)
  total_sql.join(";\n")
end
default_insert_value(column) click to toggle source
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 458
def default_insert_value(column)
  DEFAULT_INSERT_VALUE
end
execute_batch(statements, name = nil) click to toggle source
# 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
last_inserted_id(result) click to toggle source
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 543
def last_inserted_id(result)
  single_value_from_rows(result.rows)
end
select(sql, name = nil, binds = []) click to toggle source

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
select_prepared(sql, name = nil, binds = []) click to toggle source
# 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
single_value_from_rows(rows) click to toggle source
# 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
sql_for_insert(sql, pk, binds) click to toggle source
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 539
def sql_for_insert(sql, pk, binds)
  [sql, binds]
end
with_multi_statements() { || ... } click to toggle source
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 522
def with_multi_statements
  yield
end