Module: ActiveRecord::ConnectionAdapters::DatabaseStatements

Included in:
AbstractAdapter
Defined in:
activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Instance Attribute Details

#transaction_managerObject (readonly)

:nodoc:


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 219

def transaction_manager
  @transaction_manager
end

Instance Method Details

#add_transaction_record(record) ⇒ Object

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


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 233

def add_transaction_record(record)
  current_transaction.add_record(record)
end

#begin_db_transactionObject

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


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 242

def begin_db_transaction()    end

#begin_isolated_db_transaction(isolation) ⇒ Object

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


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 256

def begin_isolated_db_transaction(isolation)
  raise ActiveRecord::TransactionIsolationError, "adapter does not support setting transaction isolation"
end

#cacheable_query(arel) ⇒ Object

This is used in the StatementCache object. It returns an object that can be used to query the database repeatedly.


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 21

def cacheable_query(arel) # :nodoc:
  if prepared_statements
    ActiveRecord::StatementCache.query visitor, arel.ast
  else
    ActiveRecord::StatementCache.partial_query visitor, arel.ast, collector
  end
end

#commit_db_transactionObject

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


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 261

def commit_db_transaction()   end

#default_sequence_name(table, column) ⇒ Object


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 278

def default_sequence_name(table, column)
  nil
end

#delete(arel, name = nil, binds = []) ⇒ Object

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


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 118

def delete(arel, name = nil, binds = [])
  exec_delete(to_sql(arel, binds), name, binds)
end

#empty_insert_statement_valueObject


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 306

def empty_insert_statement_value
  "DEFAULT VALUES"
end

#exec_delete(sql, name, binds) ⇒ Object

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.


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 82

def exec_delete(sql, name, binds)
  exec_query(sql, name, binds)
end

#exec_insert(sql, name, binds, pk = nil, sequence_name = nil) ⇒ Object

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.


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 75

def exec_insert(sql, name, binds, pk = nil, sequence_name = nil)
  exec_query(sql, name, binds)
end

#exec_query(sql, name = 'SQL', binds = []) ⇒ Object

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


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 69

def exec_query(sql, name = 'SQL', binds = [])
end

#exec_rollback_db_transactionObject

:nodoc:


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 269

def exec_rollback_db_transaction() end

#exec_rollback_to_savepoint(name = nil) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 275

def exec_rollback_to_savepoint(name = nil) #:nodoc:
end

#exec_update(sql, name, binds) ⇒ Object

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.


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 94

def exec_update(sql, name, binds)
  exec_query(sql, name, binds)
end

#execute(sql, name = nil) ⇒ Object

Executes the SQL statement in the context of this connection.


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 62

def execute(sql, name = nil)
end

#initializeObject


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 4

def initialize
  super
  reset_transaction
end

#insert(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = []) ⇒ Object

Returns the last auto-generated ID from the affected table.

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.


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 106

def insert(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = [])
  sql, binds = sql_for_insert(to_sql(arel, binds), pk, id_value, sequence_name, binds)
  value      = exec_insert(sql, name, binds, pk, sequence_name)
  id_value || last_inserted_id(value)
end

#insert_fixture(fixture, table_name) ⇒ Object

Inserts the given fixture into the table. Overridden in adapters that require something beyond a simple insert (eg. Oracle).


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 289

def insert_fixture(fixture, table_name)
  fixture = fixture.stringify_keys
  columns = schema_cache.columns_hash(table_name)

  key_list   = []
  value_list = fixture.map do |name, value|
    if column = columns[name]
      key_list << quote_column_name(name)
      quote(value, column)
    else
      raise Fixture::FixtureError, %(table "#{table_name}" has no column named #{name.inspect}.)
    end
  end

  execute "INSERT INTO #{quote_table_name(table_name)} (#{key_list.join(', ')}) VALUES (#{value_list.join(', ')})", 'Fixture Insert'
end

#join_to_delete(delete, select, key) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 339

def join_to_delete(delete, select, key) #:nodoc:
  subselect = subquery_for(key, select)

  delete.where key.in(subselect)
end

#join_to_update(update, select) ⇒ Object

The default strategy for an UPDATE with joins is to use a subquery. This doesn't work on MySQL (even when aliasing the tables), but MySQL allows using JOIN directly in an UPDATE statement, so in the MySQL adapters we redefine this to do that.


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 332

def join_to_update(update, select) #:nodoc:
  key = update.key
  subselect = subquery_for(key, select)

  update.where key.in(subselect)
end

#reset_sequence!(table, column, sequence = nil) ⇒ Object

Set the sequence to the max value of the table's column.


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 283

def reset_sequence!(table, column, sequence = nil)
  # Do nothing by default. Implement for PostgreSQL, Oracle, ...
end

#reset_transactionObject

:nodoc:


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 227

def reset_transaction #:nodoc:
  @transaction_manager = TransactionManager.new(self)
end

#rollback_db_transactionObject

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


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 265

def rollback_db_transaction
  exec_rollback_db_transaction
end

#rollback_to_savepoint(name = nil) ⇒ Object


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 271

def rollback_to_savepoint(name = nil)
  exec_rollback_to_savepoint(name)
end

#sanitize_limit(limit) ⇒ Object

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 a comma-delimited list of integers, or an Arel SQL literal.

Returns Integer and Arel::Nodes::SqlLiteral limits as is. Returns the sanitized limit parameter, either as an integer, or as a string which contains a comma-delimited list of integers.


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 319

def sanitize_limit(limit)
  if limit.is_a?(Integer) || limit.is_a?(Arel::Nodes::SqlLiteral)
    limit
  elsif limit.to_s.include?(',')
    Arel.sql limit.to_s.split(',').map{ |i| Integer(i) }.join(',')
  else
    Integer(limit)
  end
end

#select_all(arel, name = nil, binds = []) ⇒ Object

Returns an ActiveRecord::Result instance.


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 30

def select_all(arel, name = nil, binds = [])
  arel, binds = binds_from_relation arel, binds
  select(to_sql(arel, binds), name, binds)
end

#select_one(arel, name = nil, binds = []) ⇒ Object

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


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 37

def select_one(arel, name = nil, binds = [])
  select_all(arel, name, binds).first
end

#select_rows(sql, name = nil, binds = []) ⇒ Object

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


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 57

def select_rows(sql, name = nil, binds = [])
end

#select_value(arel, name = nil, binds = []) ⇒ Object

Returns a single value from a record


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 42

def select_value(arel, name = nil, binds = [])
  if result = select_one(arel, name, binds)
    result.values.first
  end
end

#select_values(arel, name = nil) ⇒ Object

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

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

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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 50

def select_values(arel, name = nil)
  arel, binds = binds_from_relation arel, []
  select_rows(to_sql(arel, binds), name, binds).map(&:first)
end

#supports_statement_cache?Boolean

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


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 124

def supports_statement_cache?
  false
end

#to_sql(arel, binds = []) ⇒ Object

Converts an arel AST to SQL


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# 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.dup, self)
  else
    arel
  end
end

#transaction(options = {}) ⇒ Object

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/5.0/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 mysql, mysql2 and postgresql adapters support setting the transaction isolation level. However, support is disabled for MySQL versions below 5, because they are affected by a bug which means the isolation level gets persisted outside the transaction.


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 204

def transaction(options = {})
  options.assert_valid_keys :requires_new, :joinable, :isolation

  if !options[:requires_new] && current_transaction.joinable?
    if options[:isolation]
      raise ActiveRecord::TransactionIsolationError, "cannot set isolation when joining a transaction"
    end
    yield
  else
    transaction_manager.within_new_transaction(options) { yield }
  end
rescue ActiveRecord::Rollback  # rollbacks are silently swallowed

end

#transaction_isolation_levelsObject


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 244

def transaction_isolation_levels
  {
    read_uncommitted: "READ UNCOMMITTED",
    read_committed:   "READ COMMITTED",
    repeatable_read:  "REPEATABLE READ",
    serializable:     "SERIALIZABLE"
  }
end

#transaction_open?Boolean


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 223

def transaction_open?
  current_transaction.open?
end

#transaction_stateObject


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 237

def transaction_state
  current_transaction.state
end

#truncate(table_name, name = nil) ⇒ Object

Executes the truncate statement.

Raises:

  • (NotImplementedError)

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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 87

def truncate(table_name, name = nil)
  raise NotImplementedError
end

#update(arel, name = nil, binds = []) ⇒ Object

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


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 113

def update(arel, name = nil, binds = [])
  exec_update(to_sql(arel, binds), name, binds)
end