Methods
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Instance Public methods
add_limit!(sql, options)

Alias for add_limit_offset!.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 185
def add_limit!(sql, options)
  add_limit_offset!(sql, options) if options
end
add_limit_offset!(sql, options)

Appends LIMITand OFFSEToptions to an SQL statement, or some SQL fragment that has the same semantics as LIMIT and OFFSET.

optionsmust be a Hash which contains a :limitoption (required) and an :offsetoption (optional).

This method modifiesthe sqlparameter.

Examples
add_limit_offset!('SELECT * FROM suppliers', {:limit => 10, :offset => 50})

generates

SELECT * FROM suppliers LIMIT 10 OFFSET 50
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 201
def add_limit_offset!(sql, options)
  if limit = options[:limit]
    sql << " LIMIT #{sanitize_limit(limit)}"
    if offset = options[:offset]
      sql << " OFFSET #{offset.to_i}"
    end
  end
  sql
end
add_lock!(sql, options)

Appends a locking clause to an SQL statement. This method modifiesthe sqlparameter.

# SELECT * FROM suppliers FOR UPDATE
add_lock! 'SELECT * FROM suppliers', :lock => true
add_lock! 'SELECT * FROM suppliers', :lock => ' FOR UPDATE'
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 216
def add_lock!(sql, options)
  case lock = options[:lock]
    when true;   sql << ' FOR UPDATE'
    when String; sql << " #{lock}"
  end
end
begin_db_transaction()

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

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 175
def begin_db_transaction()    end
case_sensitive_equality_operator()
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 242
def case_sensitive_equality_operator
  "="
end
commit_db_transaction()

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

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 178
def commit_db_transaction()   end
default_sequence_name(table, column)
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 223
def default_sequence_name(table, column)
  nil
end
delete(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 53
def delete(sql, name = nil)
  delete_sql(sql, name)
end
empty_insert_statement(table_name)
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 238
def empty_insert_statement(table_name)
  "INSERT INTO #{quote_table_name(table_name)} VALUES(DEFAULT)"
end
execute(sql, name = nil, skip_logging = false)

Executes the SQL statement in the context of this connection.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 38
def execute(sql, name = nil, skip_logging = false)
end
insert(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 43
def insert(sql, name = nil, pk = nil, id_value = nil, sequence_name = nil)
  insert_sql(sql, name, pk, id_value, sequence_name)
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 234
def insert_fixture(fixture, table_name)
  execute "INSERT INTO #{quote_table_name(table_name)} (#{fixture.key_list}) VALUES (#{fixture.value_list})", '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 246
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
outside_transaction?()

Checks whether there is currently no transaction active. This is done by querying the database driver, and does not use the transaction house-keeping information recorded by increment_open_transactions and friends.

Returns true if there is no transaction active, false if there is a transaction active, and nil if this information is unknown.

Not all adapters supports transaction state introspection. Currently, only the PostgreSQL adapter supports this.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 67
def outside_transaction?
  nil
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 228
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 182
def rollback_db_transaction() end
select_all(sql, name = nil)

Returns an array of record hashes with the column names as keys and column values as values.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 6
def select_all(sql, name = nil)
  select(sql, name)
end
select_one(sql, name = nil)

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 12
def select_one(sql, name = nil)
  result = select_all(sql, name)
  result.first if result
end
select_rows(sql, name = nil)

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 33
def select_rows(sql, name = nil)
end
select_value(sql, name = nil)

Returns a single value from a record

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 18
def select_value(sql, name = nil)
  if result = select_one(sql, name)
    result.values.first
  end
end
select_values(sql, 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 26
def select_values(sql, name = nil)
  result = select_rows(sql, name)
  result.map { |v| v[0] }
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/savepoints.html Savepoints are supported by MySQL and PostgreSQL, but not SQLite3.

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_newis 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
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 113
def transaction(options = {})
  options.assert_valid_keys :requires_new, :joinable
  last_transaction_joinable = @transaction_joinable
  if options.has_key?(:joinable)
    @transaction_joinable = options[:joinable]
  else
    @transaction_joinable = true
  end
  requires_new = options[:requires_new] || !last_transaction_joinable
  transaction_open = false
  begin
    if block_given?
      if requires_new || open_transactions == 0
        if open_transactions == 0
          begin_db_transaction
        elsif requires_new
          create_savepoint
        end
        increment_open_transactions
        transaction_open = true
      end
      yield
    end
  rescue Exception => database_transaction_rollback
    if transaction_open && !outside_transaction?
      transaction_open = false
      decrement_open_transactions
      if open_transactions == 0
        rollback_db_transaction
      else
        rollback_to_savepoint
      end
    end
    raise unless database_transaction_rollback.is_a?(ActiveRecord::Rollback)
  end
ensure
  @transaction_joinable = last_transaction_joinable
  if outside_transaction?
    @open_transactions = 0
  elsif transaction_open
    decrement_open_transactions
    begin
      if open_transactions == 0
        commit_db_transaction
      else
        release_savepoint
      end
    rescue Exception => database_transaction_rollback
      if open_transactions == 0
        rollback_db_transaction
      else
        rollback_to_savepoint
      end
      raise
    end
  end
end
update(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 48
def update(sql, name = nil)
  update_sql(sql, name)
end
Instance Protected methods
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 269
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 258
def insert_sql(sql, name = nil, pk = nil, id_value = nil, sequence_name = nil)
  execute(sql, name)
  id_value
end
sanitize_limit(limit)

Sanitizes the given LIMIT parameter in order to prevent SQL injection.

limitmay be anything that can evaluate to a string via to_s. It should look like an integer, or a comma-delimited list of integers.

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 280
def sanitize_limit(limit)
  if limit.to_s =~ /,/
    limit.to_s.split(',').map{ |i| i.to_i }.join(',')
  else
    limit.to_i
  end
end
select(sql, name = nil)

Returns an array of record hashes with the column names as keys and column values as values.

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 253
def select(sql, name = nil)
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 264
def update_sql(sql, name = nil)
  execute(sql, name)
end