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Class Public methods
new()
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 4
def initialize
  super
  reset_transaction
end
Instance Public methods
add_transaction_record(record)

Register a record with the current transaction so that its after_commit and after_rollback callbacks can be called.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 228
def add_transaction_record(record)
  current_transaction.add_record(record)
end
begin_db_transaction()

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

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 233
def begin_db_transaction()    end
begin_isolated_db_transaction(isolation)

Begins the transaction with the isolation level set. Raises an error by default; adapters that support setting the isolation level should implement this method.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 247
def begin_isolated_db_transaction(isolation)
  raise ActiveRecord::TransactionIsolationError, "adapter does not support setting transaction isolation"
end
commit_db_transaction()

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

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 252
def commit_db_transaction()   end
default_sequence_name(table, column)
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 258
def default_sequence_name(table, column)
  nil
end
delete(arel, name = nil, binds = [])

Executes the delete statement and returns the number of rows affected.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 113
def delete(arel, name = nil, binds = [])
  exec_delete(to_sql(arel, binds), name, binds)
end
empty_insert_statement_value()
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 281
def empty_insert_statement_value
  "DEFAULT VALUES"
end
exec_delete(sql, name, binds)

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.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 82
def exec_delete(sql, name, binds)
  exec_query(sql, name, binds)
end
exec_insert(sql, name, binds, pk = nil, sequence_name = nil)

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.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 75
def exec_insert(sql, name, binds, pk = nil, sequence_name = nil)
  exec_query(sql, name, binds)
end
exec_query(sql, name = 'SQL', binds = [])

Executes sql statement in the context of this connection using binds as the bind substitutes. name is logged along with the executed sql statement.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 69
def exec_query(sql, name = 'SQL', binds = [])
end
exec_update(sql, name, binds)

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.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 89
def exec_update(sql, name, binds)
  exec_query(sql, name, binds)
end
execute(sql, name = nil)

Executes the SQL statement in the context of this connection.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 62
def execute(sql, name = nil)
end
insert(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = [])

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.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 101
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)

Inserts the given fixture into the table. Overridden in adapters that require something beyond a simple insert (eg. Oracle).

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 269
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
limited_update_conditions(where_sql, quoted_table_name, quoted_primary_key)
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 285
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)

Set the sequence to the max value of the table's column.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 263
def reset_sequence!(table, column, sequence = nil)
  # Do nothing by default. Implement for PostgreSQL, Oracle, ...
end
rollback_db_transaction()

Rolls back the transaction (and turns on auto-committing). Must be done if the transaction block raises an exception or returns false.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 256
def rollback_db_transaction() end
sanitize_limit(limit)

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.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 298
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 = [])

Returns an ActiveRecord::Result instance.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 30
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 = [])

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

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 37
def select_one(arel, name = nil, binds = [])
  select_all(arel, name, binds).first
end
select_rows(sql, name = nil, binds = [])

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

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 57
def select_rows(sql, name = nil, binds = [])
end
select_value(arel, name = nil, binds = [])

Returns a single value from a record

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 42
def select_value(arel, name = nil, binds = [])
  if result = select_one(arel, name, binds)
    result.values.first
  end
end
select_values(arel, name = nil)

Returns an array of the values of the first column in a select:

select_values("SELECT id FROM companies LIMIT 3") => [1,2,3]
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 50
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?()

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

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 119
def supports_statement_cache?
  false
end
to_sql(arel, binds = [])

Converts an arel AST to SQL

# File activerecord/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.dup, self)
  else
    arel
  end
end
transaction(options = {})

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.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 199
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
    transaction_manager.within_new_transaction(options) { yield }
  end
rescue ActiveRecord::Rollback
  # rollbacks are silently swallowed
end
transaction_isolation_levels()
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 235
def transaction_isolation_levels
  {
    read_uncommitted: "READ UNCOMMITTED",
    read_committed:   "READ COMMITTED",
    repeatable_read:  "REPEATABLE READ",
    serializable:     "SERIALIZABLE"
  }
end
transaction_open?()
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 218
def transaction_open?
  current_transaction.open?
end
update(arel, name = nil, binds = [])

Executes the update statement and returns the number of rows affected.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 108
def update(arel, name = nil, binds = [])
  exec_update(to_sql(arel, binds), name, binds)
end
Instance Protected methods
binds_from_relation(relation, binds)
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 363
def binds_from_relation(relation, binds)
  if relation.is_a?(Relation) && binds.empty?
    relation, binds = relation.arel, relation.bind_values
  end
  [relation, binds]
end
delete_sql(sql, name = nil)

Executes the delete statement and returns the number of rows affected.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 350
def delete_sql(sql, name = nil)
  update_sql(sql, name)
end
insert_sql(sql, name = nil, pk = nil, id_value = nil, sequence_name = nil)

Returns the last auto-generated ID from the affected table.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 339
def insert_sql(sql, name = nil, pk = nil, id_value = nil, sequence_name = nil)
  execute(sql, name)
  id_value
end
last_inserted_id(result)
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 358
def last_inserted_id(result)
  row = result.rows.first
  row && row.first
end
select(sql, name = nil, binds = [])

Returns an ActiveRecord::Result instance.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 334
def select(sql, name = nil, binds = [])
end
sql_for_insert(sql, pk, id_value, sequence_name, binds)
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 354
def sql_for_insert(sql, pk, id_value, sequence_name, binds)
  [sql, binds]
end
subquery_for(key, select)

Returns a subquery for the given key using the join information.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 327
def subquery_for(key, select)
  subselect = select.clone
  subselect.projections = [key]
  subselect
end
update_sql(sql, name = nil)

Executes the update statement and returns the number of rows affected.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 345
def update_sql(sql, name = nil)
  execute(sql, name)
end