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 247

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 252

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 266

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 229

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

#case_sensitive_equality_operatorObject


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 304

def case_sensitive_equality_operator
  "="
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 271

def commit_db_transaction()   end

#commit_transactionObject

:nodoc:


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

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 221

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 277

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 104

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 300

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 73

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 66

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 60

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 80

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 53

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 92

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 288

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 341

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 334

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 308

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 282

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 241

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 275

def rollback_db_transaction() end

#rollback_transactionObject

:nodoc:


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

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 321

def sanitize_limit(limit)
  if limit.is_a?(Integer) || limit.is_a?(Arel::Nodes::SqlLiteral)
    limit
  elsif limit.to_s =~ /,/
    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 = [])
  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 28

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

#select_rows(sql, name = nil) ⇒ 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 48

def select_rows(sql, name = nil)
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 33

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 41

def select_values(arel, name = nil)
  result = select_rows(to_sql(arel, []), name)
  result.map { |v| v[0] }
end

#supports_statement_cache?Boolean

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

Returns:

  • (Boolean)

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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 110

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 190

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 254

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

#transaction_open?Boolean

Returns:

  • (Boolean)

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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 225

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 99

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 206

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