Module: ActiveRecord::ConnectionAdapters::DatabaseStatements

Included in:
AbstractAdapter
Defined in:
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 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 231

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 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 245

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 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 254

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 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 268

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

#cacheable_query(klass, 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 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 21

def cacheable_query(klass, arel) # :nodoc:
  collected = visitor.accept(arel.ast, collector)
  if prepared_statements
    klass.query(collected.value)
  else
    klass.partial_query(collected.value)
  end
end

#commit_db_transactionObject

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


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# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 273

def commit_db_transaction()   end

#default_sequence_name(table, column) ⇒ Object


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# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 287

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 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 134

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

#empty_insert_statement_valueObject


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# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 322

def empty_insert_statement_value
  "DEFAULT VALUES"
end

#exec_delete(sql, name = nil, 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 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 98

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

#exec_insert(sql, name = nil, 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 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 90

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) ⇒ 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.

Raises:

  • (NotImplementedError)

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# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 83

def exec_query(sql, name = "SQL", binds = [], prepare: false)
  raise NotImplementedError
end

#exec_rollback_db_transactionObject

:nodoc:


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# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 281

def exec_rollback_db_transaction() end

#exec_update(sql, name = nil, 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 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 110

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

#execute(sql, name = nil) ⇒ Object

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.

Raises:

  • (NotImplementedError)

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# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 76

def execute(sql, name = nil)
  raise NotImplementedError
end

#initializeObject


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# File '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 Also known as: create

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.


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# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 122

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

#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 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 298

def insert_fixture(fixture, table_name)
  fixture = fixture.stringify_keys

  columns = schema_cache.columns_hash(table_name)
  binds = fixture.map do |name, value|
    if column = columns[name]
      type = lookup_cast_type_from_column(column)
      Relation::QueryAttribute.new(name, value, type)
    else
      raise Fixture::FixtureError, %(table "#{table_name}" has no column named #{name.inspect}.)
    end
  end
  key_list = fixture.keys.map { |name| quote_column_name(name) }
  value_list = binds.map(&:value_for_database).map do |value|
    begin
      quote(value)
    rescue TypeError
      quote(YAML.dump(value))
    end
  end

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

#join_to_update(update, select, key) ⇒ Object Also known as: join_to_delete

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 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 343

def join_to_update(update, select, key) # :nodoc:
  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 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 292

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

#reset_transactionObject

:nodoc:


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# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 239

def reset_transaction #:nodoc:
  @transaction_manager = ConnectionAdapters::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 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 277

def rollback_db_transaction
  exec_rollback_db_transaction
end

#rollback_to_savepoint(name = nil) ⇒ Object


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

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 an Arel SQL literal.

Returns Integer and Arel::Nodes::SqlLiteral limits as is.


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

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) ⇒ Object

Returns an ActiveRecord::Result instance.


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# File '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 = []) ⇒ Object

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


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# File '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 = []) ⇒ Object

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


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# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 67

def select_rows(arel, name = nil, binds = [])
  select_all(arel, name, binds).rows
end

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

Returns a single value from a record


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# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 53

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

#select_values(arel, name = nil, binds = []) ⇒ 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 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 61

def select_values(arel, name = nil, binds = [])
  select_rows(arel, name, binds).map(&:first)
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 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 140

def supports_statement_cache?
  false
end

#to_sql(arel, binds = []) ⇒ Object

Converts an arel AST to SQL


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# File '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) ⇒ 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/5.7/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.


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# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 218

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_levelsObject


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

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 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 235

def transaction_open?
  current_transaction.open?
end

#transaction_stateObject


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# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 249

def transaction_state
  current_transaction.state
end

#truncate(table_name, name = nil) ⇒ Object

Executes the truncate statement.

Raises:

  • (NotImplementedError)

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# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 103

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 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 129

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