Module: ActiveRecord::ConnectionAdapters::DatabaseStatements

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

Instance Method Summary collapse

Instance Method Details

#add_limit!(sql, options) ⇒ Object

Alias for add_limit_offset!.



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# File '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) ⇒ Object

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

options must be a Hash which contains a :limit option (required) and an :offset option (optional).

This method modifies the sql parameter.

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

generates

SELECT * FROM suppliers LIMIT 10 OFFSET 50



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# File '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) ⇒ Object

Appends a locking clause to an SQL statement. This method modifies the sql parameter.

# SELECT * FROM suppliers FOR UPDATE
add_lock! 'SELECT * FROM suppliers', :lock => true
add_lock! 'SELECT * FROM suppliers', :lock => ' FOR UPDATE'



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# File '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 ⇒ Object

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



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# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 175

def begin_db_transaction()    end

#case_sensitive_equality_operator ⇒ Object 



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# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 242

def case_sensitive_equality_operator
  "="
end

#commit_db_transaction ⇒ Object

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



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# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 178

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 223

def default_sequence_name(table, column)
  nil
end

#delete(sql, name = nil) ⇒ 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 53

def delete(sql, name = nil)
  delete_sql(sql, name)
end

#empty_insert_statement(table_name) ⇒ Object 



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# File '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) ⇒ Object

Executes the SQL statement in the context of this connection.



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# File '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) ⇒ Object

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



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# File '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) ⇒ 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 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) ⇒ Object 



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# File '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? ⇒ Boolean

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.

Returns:

  • (Boolean) 


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

def outside_transaction?
  nil
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 228

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

#rollback_db_transaction ⇒ Object

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 182

def rollback_db_transaction() end

#select_all(sql, name = nil) ⇒ Object

Returns an array of record hashes 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 6

def select_all(sql, name = nil)
  select(sql, name)
end

#select_one(sql, name = nil) ⇒ 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 12

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

#select_rows(sql, name = nil) ⇒ 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 33

def select_rows(sql, name = nil)
end

#select_value(sql, name = nil) ⇒ Object

Returns a single value from a record



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# File '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) ⇒ 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 26

def select_values(sql, name = nil)
  result = select_rows(sql, name)
  result.map { |v| v[0] }
end

#transaction(options = {}) ⇒ 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/5.0/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_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



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# File '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) ⇒ 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 48

def update(sql, name = nil)
  update_sql(sql, name)
end