Module: ActiveRecord::ConnectionAdapters::DatabaseStatements

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

Instance Method Summary collapse

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 248

def add_transaction_record(record)
  @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 253

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 267

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

#begin_transaction(options = {}) ⇒ Object

:nodoc:



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 230

def begin_transaction(options = {}) #:nodoc:
  @transaction = @transaction.begin(options)
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 272

def commit_db_transaction()   end

#commit_transactionObject

:nodoc:



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 234

def commit_transaction #:nodoc:
  @transaction = @transaction.commit
end

#current_transactionObject

:nodoc:



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 222

def current_transaction #:nodoc:
  @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 105

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 301

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 74

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 67

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 61

def exec_query(sql, name = 'SQL', binds = [])
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 81

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 54

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 93

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)
  columns = schema_cache.columns_hash(table_name)

  key_list   = []
  value_list = fixture.map do |name, value|
    key_list << quote_column_name(name)
    quote(value, columns[name])
  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 338

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 331

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

  update.where key.in(subselect)
end

#limited_update_conditions(where_sql, quoted_table_name, quoted_primary_key) ⇒ Object



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 305

def limited_update_conditions(where_sql, quoted_table_name, quoted_primary_key)
  "WHERE #{quoted_primary_key} IN (SELECT #{quoted_primary_key} FROM #{quoted_table_name} #{where_sql})"
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 242

def reset_transaction #:nodoc:
  @transaction = ClosedTransaction.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 276

def rollback_db_transaction() end

#rollback_transactionObject

:nodoc:



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 238

def rollback_transaction #:nodoc:
  @transaction = @transaction.rollback
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 318

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 22

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 29

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 49

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 34

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 42

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 111

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)
    binds = binds.dup
    visitor.accept(arel.ast) do
      quote(*binds.shift.reverse)
    end
  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 191

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
    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 255

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 226

def transaction_open?
  @transaction.open?
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 100

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

#within_new_transaction(options = {}) ⇒ Object

:nodoc:



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 207

def within_new_transaction(options = {}) #:nodoc:
  transaction = begin_transaction(options)
  yield
rescue Exception => error
  rollback_transaction if transaction
  raise
ensure
  begin
    commit_transaction unless error
  rescue Exception
    rollback_transaction
    raise
  end
end