Module: ActiveRecord::ConnectionAdapters::DatabaseStatements

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

Defined Under Namespace

Classes: PartialQueryCollector

Instance Attribute Summary collapse

Instance Method Summary collapse

Instance Attribute Details

#transaction_managerObject (readonly)

:nodoc:


260
261
262
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 260

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.


274
275
276
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 274

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

#begin_db_transactionObject

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


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

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.


297
298
299
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 297

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.


33
34
35
36
37
38
39
40
41
42
43
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 33

def cacheable_query(klass, arel) # :nodoc:
  if prepared_statements
    sql, binds = visitor.accept(arel.ast, collector).value
    query = klass.query(sql)
  else
    collector = PartialQueryCollector.new
    parts, binds = visitor.accept(arel.ast, collector).value
    query = klass.partial_query(parts)
  end
  [query, binds]
end

#commit_db_transactionObject

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


302
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 302

def commit_db_transaction()   end

#default_sequence_name(table, column) ⇒ Object


316
317
318
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 316

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.


161
162
163
164
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 161

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

#empty_insert_statement_valueObject


388
389
390
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 388

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.


123
124
125
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 123

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.


115
116
117
118
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 115

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)

108
109
110
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 108

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

#exec_rollback_db_transactionObject

:nodoc:


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

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.


135
136
137
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 135

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)

101
102
103
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 101

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

#initializeObject


6
7
8
9
# File '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.


147
148
149
150
151
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 147

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 (eg. Oracle). Most of adapters should implement `insert_fixtures` that leverages bulk SQL insert. We keep this method to provide fallback for databases like sqlite that do not support bulk inserts.


330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 330

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

  table = Arel::Table.new(table_name)

  values = binds.map do |bind|
    value = with_yaml_fallback(bind.value_for_database)
    [table[bind.name], value]
  end

  manager = Arel::InsertManager.new
  manager.into(table)
  manager.insert(values)
  execute manager.to_sql, "Fixture Insert"
end

#insert_fixtures(fixtures, table_name) ⇒ Object

Inserts a set of fixtures into the table. Overridden in adapters that require something beyond a simple insert (eg. Oracle).


358
359
360
361
362
363
364
365
366
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 358

def insert_fixtures(fixtures, table_name)
  ActiveSupport::Deprecation.warn(<<-MSG.squish)
    `insert_fixtures` is deprecated and will be removed in the next version of Rails.
    Consider using `insert_fixtures_set` for performance improvement.
  MSG
  return if fixtures.empty?

  execute(build_fixture_sql(fixtures, table_name), "Fixtures Insert")
end

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


368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 368

def insert_fixtures_set(fixture_set, tables_to_delete = [])
  fixture_inserts = fixture_set.map do |table_name, fixtures|
    next if fixtures.empty?

    build_fixture_sql(fixtures, table_name)
  end.compact

  table_deletes = tables_to_delete.map { |table| "DELETE FROM #{quote_table_name table}".dup }
  total_sql = Array.wrap(combine_multi_statements(table_deletes + fixture_inserts))

  disable_referential_integrity do
    transaction(requires_new: true) do
      total_sql.each do |sql|
        execute sql, "Fixtures Load"
        yield if block_given?
      end
    end
  end
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.


409
410
411
412
413
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 409

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

  update.where key.in(subselect)
end

#query(sql, name = nil) ⇒ Object

:nodoc:


92
93
94
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 92

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

#query_value(sql, name = nil) ⇒ Object

:nodoc:


84
85
86
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 84

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

#query_values(sql, name = nil) ⇒ Object

:nodoc:


88
89
90
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 88

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.


321
322
323
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 321

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

#reset_transactionObject

:nodoc:


268
269
270
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 268

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.


306
307
308
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 306

def rollback_db_transaction
  exec_rollback_db_transaction
end

#rollback_to_savepoint(name = nil) ⇒ Object


312
313
314
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 312

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.


398
399
400
401
402
403
404
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 398

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.


46
47
48
49
50
51
52
53
54
55
56
57
58
59
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 46

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


63
64
65
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 63

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.


80
81
82
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 80

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


68
69
70
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 68

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]

74
75
76
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 74

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)

168
169
170
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 168

def supports_statement_cache? # :nodoc:
  true
end

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

Converts an arel AST to SQL


12
13
14
15
# File '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

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.


247
248
249
250
251
252
253
254
255
256
257
258
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 247

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


285
286
287
288
289
290
291
292
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 285

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

#transaction_open?Boolean

Returns:

  • (Boolean)

264
265
266
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 264

def transaction_open?
  current_transaction.open?
end

#transaction_stateObject


278
279
280
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 278

def transaction_state
  current_transaction.state
end

#truncate(table_name, name = nil) ⇒ Object

Executes the truncate statement.

Raises:

  • (NotImplementedError)

128
129
130
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 128

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.


155
156
157
158
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 155

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