ActiveRecord::ConnectionAdapters::DatabaseStatements

new() Link

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 4
def initialize
  super
  reset_transaction
end

add_transaction_record(record) Link

Register a record with the current transaction so that its after_commit and after_rollback callbacks can be called.

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 255
def add_transaction_record(record)
  current_transaction.add_record(record)
end

begin_db_transaction() Link

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

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 264
def begin_db_transaction()    end

begin_isolated_db_transaction(isolation) Link

Begins the transaction with the isolation level set. Raises an error by default; adapters that support setting the isolation level should implement this method.

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 278
def begin_isolated_db_transaction(isolation)
  raise ActiveRecord::TransactionIsolationError, "adapter does not support setting transaction isolation"
end

commit_db_transaction() Link

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

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 283
def commit_db_transaction()   end

create(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = []) Link

Alias for: insert

delete(arel, name = nil, binds = []) Link

Executes the delete statement and returns the number of rows affected.

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 144
def delete(arel, name = nil, binds = [])
  exec_delete(to_sql(arel, binds), name, binds)
end

exec_delete(sql, name = nil, binds = []) Link

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.

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 108
def exec_delete(sql, name = nil, binds = [])
  exec_query(sql, name, binds)
end

exec_insert(sql, name = nil, binds = [], pk = nil, sequence_name = nil) Link

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.

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 100
def exec_insert(sql, name = nil, binds = [], pk = nil, sequence_name = nil)
  sql, binds = sql_for_insert(sql, pk, nil, sequence_name, binds)
  exec_query(sql, name, binds)
end

exec_query(sql, name = "SQL", binds = [], prepare: false) Link

Executes sql statement in the context of this connection using binds as the bind substitutes. name is logged along with the executed sql statement.

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 93
def exec_query(sql, name = "SQL", binds = [], prepare: false)
  raise NotImplementedError
end

exec_update(sql, name = nil, binds = []) Link

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.

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 120
def exec_update(sql, name = nil, binds = [])
  exec_query(sql, name, binds)
end

execute(sql, name = nil) Link

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.

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 86
def execute(sql, name = nil)
  raise NotImplementedError
end

insert(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = []) Link

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

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 132
def insert(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = [])
  value = exec_insert(to_sql(arel, binds), name, binds, pk, sequence_name)
  id_value || last_inserted_id(value)
end

rollback_db_transaction() Link

Rolls back the transaction (and turns on auto-committing). Must be done if the transaction block raises an exception or returns false.

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 287
def rollback_db_transaction
  exec_rollback_db_transaction
end

select_all(arel, name = nil, binds = [], preparable: nil) Link

Returns an ActiveRecord::Result instance.

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 31
def select_all(arel, name = nil, binds = [], preparable: nil)
  arel, binds = binds_from_relation arel, binds
  sql = to_sql(arel, binds)
  if !prepared_statements || (arel.is_a?(String) && preparable.nil?)
    preparable = false
  else
    preparable = visitor.preparable
  end
  if prepared_statements && preparable
    select_prepared(sql, name, binds)
  else
    select(sql, name, binds)
  end
end

select_one(arel, name = nil, binds = []) Link

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

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 48
def select_one(arel, name = nil, binds = [])
  select_all(arel, name, binds).first
end

select_rows(arel, name = nil, binds = []) Link

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

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 65
def select_rows(arel, name = nil, binds = [])
  select_all(arel, name, binds).rows
end

select_value(arel, name = nil, binds = []) Link

Returns a single value from a record

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 53
def select_value(arel, name = nil, binds = [])
  single_value_from_rows(select_rows(arel, name, binds))
end

select_values(arel, name = nil, binds = []) Link

Returns an array of the values of the first column in a select:

select_values("SELECT id FROM companies LIMIT 3") => [1,2,3]

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 59
def select_values(arel, name = nil, binds = [])
  select_rows(arel, name, binds).map(&:first)
end

supports_statement_cache?() Link

Returns true when the connection adapter supports prepared statement caching, otherwise returns false

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 150
def supports_statement_cache?
  false
end

to_sql(arel, binds = []) Link

Converts an arel AST to SQL

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 10
def to_sql(arel, binds = [])
  if arel.respond_to?(:ast)
    collected = visitor.accept(arel.ast, collector)
    collected.compile(binds, self).freeze
  else
    arel.dup.freeze
  end
end

transaction(requires_new: nil, isolation: nil, joinable: true) Link

Runs the given block in a database transaction, and returns the result of the block.

Nested transactions support

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/5.7/en/savepoint.html Savepoints are supported by MySQL and PostgreSQL. SQLite3 version >= '3.6.8' supports savepoints.

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.

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.

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 228
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() Link

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 266
def transaction_isolation_levels
  {
    read_uncommitted: "READ UNCOMMITTED",
    read_committed:   "READ COMMITTED",
    repeatable_read:  "REPEATABLE READ",
    serializable:     "SERIALIZABLE"
  }
end

transaction_open?() Link

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 245
def transaction_open?
  current_transaction.open?
end

transaction_state() Link

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 259
def transaction_state
  current_transaction.state
end

truncate(table_name, name = nil) Link

Executes the truncate statement.

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 113
def truncate(table_name, name = nil)
  raise NotImplementedError
end

update(arel, name = nil, binds = []) Link

Executes the update statement and returns the number of rows affected.

Source: show | on GitHub

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 139
def update(arel, name = nil, binds = [])
  exec_update(to_sql(arel, binds), name, binds)
end

Module ActiveRecord::ConnectionAdapters::DatabaseStatements

Nested transactions support

Caveats

Transaction isolation