Module: ActiveRecord::ConnectionAdapters::DatabaseStatements

Defined in:
activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb

Instance Method Summary (collapse)

Instance Method Details

- (Object) add_limit_offset!(sql, options)

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 and an :offset option.

This method modifies the sql parameter.

This method is deprecated!! Stop using it!

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

generates

SELECT * FROM suppliers LIMIT 10 OFFSET 50


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 271

def add_limit_offset!(sql, options)
  if limit = options[:limit]
    sql << " LIMIT #{sanitize_limit(limit)}"
  end
  if offset = options[:offset]
    sql << " OFFSET #{offset.to_i}"
  end
  sql
end

- (Object) add_transaction_record(record)

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 242

def add_transaction_record(record)
  last_batch = @_current_transaction_records.last
  last_batch << record if last_batch
end

- (Object) begin_db_transaction

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



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 248

def begin_db_transaction()    end

- (Object) case_sensitive_equality_operator



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 309

def case_sensitive_equality_operator
  "="
end

- (Object) commit_db_transaction

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



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 251

def commit_db_transaction()   end

- (Object) default_sequence_name(table, column)



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 282

def default_sequence_name(table, column)
  nil
end

- (Object) delete(arel, name = nil, binds = [])

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 100

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

- (Object) empty_insert_statement_value



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 305

def empty_insert_statement_value
  "VALUES(DEFAULT)"
end

- (Object) exec_delete(sql, name, binds)

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



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

def exec_delete(sql, name, binds)
  exec_query(sql, name, binds)
end

- (Object) exec_insert(sql, name, binds)

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



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 62

def exec_insert(sql, name, binds)
  exec_query(sql, name, binds)
end

- (Object) 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.



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 56

def exec_query(sql, name = 'SQL', binds = [])
end

- (Object) exec_update(sql, name, binds)

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



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

def exec_update(sql, name, binds)
  exec_query(sql, name, binds)
end

- (Object) execute(sql, name = nil)

Executes the SQL statement in the context of this connection.



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 49

def execute(sql, name = nil)
end

- (Object) 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.



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

def insert(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = [])
  sql, binds = sql_for_insert(to_sql(arel), pk, id_value, sequence_name, binds)
  value      = exec_insert(sql, name, binds)
  id_value || last_inserted_id(value)
end

- (Object) insert_fixture(fixture, table_name)

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



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 293

def insert_fixture(fixture, table_name)
  columns = Hash[columns(table_name).map { |c| [c.name, c] }]

  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

- (Object) join_to_update(update, select)

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.



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 339

def join_to_update(update, select) #:nodoc:
  subselect = select.clone
  subselect.projections = [update.key]

  update.where update.key.in(subselect)
end

- (Object) limited_update_conditions(where_sql, quoted_table_name, quoted_primary_key)



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

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

- (Boolean) 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.



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 114

def outside_transaction?
  nil
end

- (Object) reset_sequence!(table, column, sequence = nil)

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 287

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

- (Object) 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.



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 255

def rollback_db_transaction() end

- (Object) 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.



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 326

def sanitize_limit(limit)
  if limit.is_a?(Integer) || limit.is_a?(Arel::Nodes::SqlLiteral)
    limit
  elsif limit.to_s =~ /,/
    Arel.sql limit.to_s.split(',').map{ |i| Integer(i) }.join(',')
  else
    Integer(limit)
  end
end

- (Object) select_all(arel, name = nil, binds = [])

Returns an array of record hashes 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 17

def select_all(arel, name = nil, binds = [])
  select(to_sql(arel), name, binds)
end

- (Object) select_one(arel, name = nil)

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 23

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

- (Object) select_rows(sql, name = nil)

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 44

def select_rows(sql, name = nil)
end

- (Object) select_value(arel, name = nil)

Returns a single value from a record



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 29

def select_value(arel, name = nil)
  if result = select_one(arel, name)
    result.values.first
  end
end

- (Object) 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]


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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 37

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

- (Boolean) supports_statement_cache?

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



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 120

def supports_statement_cache?
  false
end

- (Object) to_sql(arel)

Converts an arel AST to SQL



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 7

def to_sql(arel)
  if arel.respond_to?(:ast)
    visitor.accept(arel.ast)
  else
    arel
  end
end

- (Object) 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_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 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 166

def transaction(options = {})
  options.assert_valid_keys :requires_new, :joinable

  last_transaction_joinable = defined?(@transaction_joinable) ? @transaction_joinable : nil
  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
  @_current_transaction_records ||= []

  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
        @_current_transaction_records.push([])
      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
        rollback_transaction_records(true)
      else
        rollback_to_savepoint
        rollback_transaction_records(false)
      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
        commit_transaction_records
      else
        release_savepoint
        save_point_records = @_current_transaction_records.pop
        unless save_point_records.blank?
          @_current_transaction_records.push([]) if @_current_transaction_records.empty?
          @_current_transaction_records.last.concat(save_point_records)
        end
      end
    rescue Exception => database_transaction_rollback
      if open_transactions == 0
        rollback_db_transaction
        rollback_transaction_records(true)
      else
        rollback_to_savepoint
        rollback_transaction_records(false)
      end
      raise
    end
  end
end

- (Object) update(arel, name = nil, binds = [])

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 95

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