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Module: ActiveRecord::ConnectionAdapters::DatabaseStatements

Instance Attribute Summary

Instance Method Summary

Instance Attribute Details

#begin_transaction (readonly)

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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 221


delegate :within_new_transaction, :open_transactions, :current_transaction, :begin_transaction, :commit_transaction, :rollback_transaction, to: :transaction_manager


  








  

    #commit_transaction   (readonly)
  

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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 221


delegate :within_new_transaction, :open_transactions, :current_transaction, :begin_transaction, :commit_transaction, :rollback_transaction, to: :transaction_manager


  








  

    #current_transaction   (readonly)
  

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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 221


delegate :within_new_transaction, :open_transactions, :current_transaction, :begin_transaction, :commit_transaction, :rollback_transaction, to: :transaction_manager


  








  

    #open_transactions   (readonly)
  

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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 221


delegate :within_new_transaction, :open_transactions, :current_transaction, :begin_transaction, :commit_transaction, :rollback_transaction, to: :transaction_manager


  








  

    #rollback_transaction   (readonly)
  

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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 221


delegate :within_new_transaction, :open_transactions, :current_transaction, :begin_transaction, :commit_transaction, :rollback_transaction, to: :transaction_manager


  








  

    #supports_statement_cache?  ⇒ Boolean  (readonly)
  



  

    

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 124


def supports_statement_cache?
  false
end


  








  

    #transaction_open?  ⇒ Boolean  (readonly)
  

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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 223


def transaction_open?
  current_transaction.open?
end


  








  

    #within_new_transaction   (readonly)
  

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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 221


delegate :within_new_transaction, :open_transactions, :current_transaction, :begin_transaction, :commit_transaction, :rollback_transaction, to: :transaction_manager


  







Instance Method Details



  

    #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 233


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


  








  

    #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 242


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.


  





  
Raises:





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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 256


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).


  



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


def commit_db_transaction()   end


  








  

    #default_sequence_name(table, column)  
  

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


def default_sequence_name(table, column)
  nil
end


  








  

    #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 118


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


  








  

    #empty_insert_statement_value  
  

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


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.


  



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# 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.


  



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# 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.


  



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# 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.


  



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


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.


  



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


def execute(sql, name = nil)
end


  








  

    #initialize  
  

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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 4


def initialize
  super
  reset_transaction
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.


  



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 106


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).


  



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 289


def insert_fixture(fixture, table_name)
  fixture = fixture.stringify_keys
  columns = schema_cache.columns_hash(table_name)

  key_list   = []
  value_list = fixture.map do |name, value|
    if column = columns[name]
      key_list << quote_column_name(name)
      quote(value, column)
    else
      raise Fixture::FixtureError, %(table "#{table_name}" has no column named #{name.inspect}.)
    end
  end

  execute "INSERT INTO #{quote_table_name(table_name)} (#{key_list.join(', ')}) VALUES (#{value_list.join(', ')})", 'Fixture Insert'
end


  








  

    #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 283


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.


  



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


def rollback_db_transaction
  exec_rollback_db_transaction
end


  








  

    #rollback_to_savepoint(name = nil)  
  

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


def rollback_to_savepoint(name = nil)
  exec_rollback_to_savepoint(name)
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.


  



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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 319


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.


  



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# 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.


  



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# 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.


  



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# 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


  



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# 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]


  



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# 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


  








  

    #to_sql(arel, binds = [])  
  



  

    

Converts an arel AST to SQL


  



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# 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.


  



  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 204


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  
  

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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 244


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


  








  

    #transaction_state  
  

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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 237


def transaction_state
  current_transaction.state
end


  








  

    #truncate(table_name, name = nil)  
  



  

    

Executes the truncate statement.


  





  
Raises:


    
  
  • 
    (NotImplementedError)
  
    • 





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# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 87


def truncate(table_name, name = nil)
  raise NotImplementedError
end


  








  

    #update(arel, name = nil, binds = [])  
  



  

    

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


  



  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb', line 113


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