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 323

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 339

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 348

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 362

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 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 48

def cacheable_query(klass, arel) # :nodoc:
  if prepared_statements
    sql, binds = visitor.compile(arel.ast, collector)
    query = klass.query(sql)
  else
    collector = klass.partial_query_collector
    parts, binds = visitor.compile(arel.ast, collector)
    query = klass.partial_query(parts)
  end
  [query, binds]
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 367

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 381

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 180

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

#empty_insert_statement_value(primary_key = nil) ⇒ Object


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 413

def empty_insert_statement_value(primary_key = nil)
  "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 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 143

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 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 135

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

#exec_insert_all(sql, name) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 154

def exec_insert_all(sql, name) # :nodoc:
  exec_query(sql, name)
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 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 128

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

#exec_rollback_db_transactionObject

:nodoc:


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 375

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 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 150

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 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 121

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

#initializeObject


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 6

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 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 166

def insert(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = [])
  sql, binds = to_sql_and_binds(arel, 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 (e.g. Oracle). Most of adapters should implement `insert_fixtures_set` that leverages bulk SQL insert. We keep this method to provide fallback for databases like sqlite that do not support bulk inserts.


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 395

def insert_fixture(fixture, table_name)
  execute(build_fixture_sql(Array.wrap(fixture), table_name), "Fixture Insert")
end

#insert_fixtures_set(fixture_set, tables_to_delete = []) ⇒ Object


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 399

def insert_fixtures_set(fixture_set, tables_to_delete = [])
  fixture_inserts = build_fixture_statements(fixture_set)
  table_deletes = tables_to_delete.map { |table| "DELETE FROM #{quote_table_name(table)}" }
  statements = table_deletes + fixture_inserts

  with_multi_statements do
    disable_referential_integrity do
      transaction(requires_new: true) do
        execute_batch(statements, "Fixtures Load")
      end
    end
  end
end

#query(sql, name = nil) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 107

def query(sql, name = nil) # :nodoc:
  exec_query(sql, name).rows
end

#query_value(sql, name = nil) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 99

def query_value(sql, name = nil) # :nodoc:
  single_value_from_rows(query(sql, name))
end

#query_values(sql, name = nil) ⇒ Object

:nodoc:


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

def query_values(sql, name = nil) # :nodoc:
  query(sql, name).map(&:first)
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 386

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 333

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 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 371

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 377

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 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 423

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 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 61

def select_all(arel, name = nil, binds = [], preparable: nil)
  arel = arel_from_relation(arel)
  sql, binds = to_sql_and_binds(arel, binds)

  if preparable.nil?
    preparable = prepared_statements ? visitor.preparable : false
  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 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 78

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 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 95

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

def select_value(arel, name = nil, binds = [])
  single_value_from_rows(select_rows(arel, name, binds))
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 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 89

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

#to_sql(arel_or_sql_string, binds = []) ⇒ Object

Converts an arel AST to SQL


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 12

def to_sql(arel_or_sql_string, binds = [])
  sql, _ = to_sql_and_binds(arel_or_sql_string, binds)
  sql
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

#transaction calls can be nested. By default, this makes all database statements in the nested transaction block become part of the parent transaction. For example, the following behavior may be surprising:

ActiveRecord::Base.transaction do
  Post.create(title: 'first')
  ActiveRecord::Base.transaction do
    Post.create(title: 'second')
    raise ActiveRecord::Rollback
  end
end

This creates both “first” and “second” posts. Reason is the ActiveRecord::Rollback exception in the nested block does not issue a ROLLBACK. Since these exceptions are captured in transaction blocks, the parent block does not see it and the real transaction is committed.

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/en/savepoint.html.

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.

In order to get a ROLLBACK for the nested transaction you may ask for a real sub-transaction by passing requires_new: true. If anything goes wrong, the database rolls back to the beginning of the sub-transaction without rolling back the parent transaction. If we add it to the previous example:

ActiveRecord::Base.transaction do
  Post.create(title: 'first')
  ActiveRecord::Base.transaction(requires_new: true) do
    Post.create(title: 'second')
    raise ActiveRecord::Rollback
  end
end

only post with title “first” is created.

See ActiveRecord::Transactions to learn more.

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 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 310

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 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 350

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 329

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 343

def transaction_state
  current_transaction.state
end

#truncate(table_name, name = nil) ⇒ Object

Executes the truncate statement.


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 186

def truncate(table_name, name = nil)
  execute(build_truncate_statement(table_name), name)
end

#truncate_tables(*table_names) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 190

def truncate_tables(*table_names) # :nodoc:
  table_names -= [schema_migration.table_name, InternalMetadata.table_name]

  return if table_names.empty?

  with_multi_statements do
    disable_referential_integrity do
      statements = build_truncate_statements(table_names)
      execute_batch(statements, "Truncate Tables")
    end
  end
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 174

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

#with_yaml_fallback(value) ⇒ Object

Fixture value is quoted by Arel, however scalar values are not quotable. In this case we want to convert the column value to YAML.


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 434

def with_yaml_fallback(value) # :nodoc:
  if value.is_a?(Hash) || value.is_a?(Array)
    YAML.dump(value)
  else
    value
  end
end

#write_query?(sql) ⇒ Boolean

Determines whether the SQL statement is a write query.

Returns:

  • (Boolean)

Raises:

  • (NotImplementedError)

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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 112

def write_query?(sql)
  raise NotImplementedError
end