Class: ActiveRecord::ConnectionAdapters::AbstractAdapter

Inherits:
Object
  • Object
show all
Includes:
DatabaseLimits, DatabaseStatements, QueryCache, Quoting, SchemaStatements, ActiveSupport::Callbacks
Defined in:
lib/active_record/connection_adapters/abstract_adapter.rb

Overview

Active Record supports multiple database systems. AbstractAdapter and related classes form the abstraction layer which makes this possible. An AbstractAdapter represents a connection to a database, and provides an abstract interface for database-specific functionality such as establishing a connection, escaping values, building the right SQL fragments for ‘:offset’ and ‘:limit’ options, etc.

All the concrete database adapters follow the interface laid down in this class. ActiveRecord::Base.connection returns an AbstractAdapter object, which you can use.

Most of the methods in the adapter are useful during migrations. Most notably, the instance methods provided by SchemaStatement are very useful.

Direct Known Subclasses

MysqlAdapter, PostgreSQLAdapter, SQLiteAdapter

Instance Attribute Summary

Attributes included from QueryCache

#query_cache, #query_cache_enabled

Instance Method Summary collapse

Methods included from QueryCache

#cache, #clear_query_cache, dirties_query_cache, included, #select_all, #uncached

Methods included from DatabaseLimits

#column_name_length, #columns_per_multicolumn_index, #columns_per_table, #in_clause_length, #index_name_length, #indexes_per_table, #joins_per_query, #sql_query_length, #table_alias_length, #table_name_length

Methods included from Quoting

#quote, #quote_column_name, #quote_string, #quoted_date, #quoted_false, #quoted_true

Methods included from DatabaseStatements

#add_limit_offset!, #add_transaction_record, #begin_db_transaction, #case_sensitive_equality_operator, #commit_db_transaction, #default_sequence_name, #delete, #empty_insert_statement_value, #execute, #insert, #insert_fixture, #limited_update_conditions, #outside_transaction?, #reset_sequence!, #rollback_db_transaction, #select_all, #select_one, #select_rows, #select_value, #select_values, #transaction, #update

Methods included from SchemaStatements

#add_column, #add_column_options!, #add_index, #add_timestamps, #assume_migrated_upto_version, #change_column, #change_column_default, #change_table, #column_exists?, #columns, #create_table, #distinct, #drop_table, #dump_schema_information, #index_exists?, #index_name, #index_name_exists?, #initialize_schema_migrations_table, #native_database_types, #remove_column, #remove_index, #remove_index!, #remove_timestamps, #rename_column, #rename_index, #rename_table, #structure_dump, #table_alias_for, #table_exists?, #type_to_sql

Constructor Details

#initialize(connection, logger = nil) ⇒ AbstractAdapter

:nodoc:



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# File 'lib/active_record/connection_adapters/abstract_adapter.rb', line 39

def initialize(connection, logger = nil) #:nodoc:
  @active = nil
  @connection, @logger = connection, logger
  @query_cache_enabled = false
  @query_cache = {}
  @instrumenter = ActiveSupport::Notifications.instrumenter
end

Instance Method Details

#active? ⇒ Boolean

Checks whether the connection to the database is still active. This includes checking whether the database is actually capable of responding, i.e. whether the connection isn’t stale.

Returns:

  • (Boolean) 


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# File 'lib/active_record/connection_adapters/abstract_adapter.rb', line 112

def active?
  @active != false
end

#adapter_name ⇒ Object

Returns the human-readable name of the adapter. Use mixed case - one can always use downcase if needed.



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# File 'lib/active_record/connection_adapters/abstract_adapter.rb', line 49

def adapter_name
  'Abstract'
end

#create_savepoint ⇒ Object 



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

def create_savepoint
end

#current_savepoint_name ⇒ Object 



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# File 'lib/active_record/connection_adapters/abstract_adapter.rb', line 187

def current_savepoint_name
  "active_record_#{open_transactions}"
end

#decrement_open_transactions ⇒ Object 



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# File 'lib/active_record/connection_adapters/abstract_adapter.rb', line 170

def decrement_open_transactions
  @open_transactions -= 1
end

#disable_referential_integrity ⇒ Object

Override to turn off referential integrity while executing &block.



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# File 'lib/active_record/connection_adapters/abstract_adapter.rb', line 103

def disable_referential_integrity
  yield
end

#disconnect! ⇒ Object

Disconnects from the database if already connected. Otherwise, this method does nothing.



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# File 'lib/active_record/connection_adapters/abstract_adapter.rb', line 124

def disconnect!
  @active = false
end

#increment_open_transactions ⇒ Object 



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# File 'lib/active_record/connection_adapters/abstract_adapter.rb', line 165

def increment_open_transactions
  @open_transactions ||= 0
  @open_transactions += 1
end

#open_transactions ⇒ Object 



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# File 'lib/active_record/connection_adapters/abstract_adapter.rb', line 161

def open_transactions
  @open_transactions ||= 0
end

#prefetch_primary_key?(table_name = nil) ⇒ Boolean

Should primary key values be selected from their corresponding sequence before the insert statement? If true, next_sequence_value is called before each insert to set the record’s primary key. This is false for all adapters but Firebird.

Returns:

  • (Boolean) 


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# File 'lib/active_record/connection_adapters/abstract_adapter.rb', line 89

def prefetch_primary_key?(table_name = nil)
  false
end

#quote_table_name(name) ⇒ Object

Override to return the quoted table name. Defaults to column quoting.



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# File 'lib/active_record/connection_adapters/abstract_adapter.rb', line 96

def quote_table_name(name)
  quote_column_name(name)
end

#raw_connection ⇒ Object

Provides access to the underlying database driver for this adapter. For example, this method returns a Mysql object in case of MysqlAdapter, and a PGconn object in case of PostgreSQLAdapter.

This is useful for when you need to call a proprietary method such as PostgreSQL’s lo_* methods.



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# File 'lib/active_record/connection_adapters/abstract_adapter.rb', line 157

def raw_connection
  @connection
end

#reconnect! ⇒ Object

Disconnects from the database if already connected, and establishes a new connection with the database.



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# File 'lib/active_record/connection_adapters/abstract_adapter.rb', line 118

def reconnect!
  @active = true
end

#release_savepoint ⇒ Object 



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# File 'lib/active_record/connection_adapters/abstract_adapter.rb', line 184

def release_savepoint
end

#requires_reloading? ⇒ Boolean

Returns true if its required to reload the connection between requests for development mode. This is not the case for Ruby/MySQL and it’s not necessary for any adapters except SQLite.

Returns:

  • (Boolean) 


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# File 'lib/active_record/connection_adapters/abstract_adapter.rb', line 140

def requires_reloading?
  false
end

#reset! ⇒ Object

Reset the state of this connection, directing the DBMS to clear transactions and other connection-related server-side state. Usually a database-dependent operation.

The default implementation does nothing; the implementation should be overridden by concrete adapters.



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# File 'lib/active_record/connection_adapters/abstract_adapter.rb', line 134

def reset!
  # this should be overridden by concrete adapters
end

#rollback_to_savepoint ⇒ Object 



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# File 'lib/active_record/connection_adapters/abstract_adapter.rb', line 181

def rollback_to_savepoint
end

#supports_count_distinct? ⇒ Boolean

Does this adapter support using DISTINCT within COUNT? This is true for all adapters except sqlite.

Returns:

  • (Boolean) 


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# File 'lib/active_record/connection_adapters/abstract_adapter.rb', line 68

def supports_count_distinct?
  true
end

#supports_ddl_transactions? ⇒ Boolean

Does this adapter support DDL rollbacks in transactions? That is, would CREATE TABLE or ALTER TABLE get rolled back by a transaction? PostgreSQL, SQL Server, and others support this. MySQL and others do not.

Returns:

  • (Boolean) 


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# File 'lib/active_record/connection_adapters/abstract_adapter.rb', line 75

def supports_ddl_transactions?
  false
end

#supports_migrations? ⇒ Boolean

Does this adapter support migrations? Backend specific, as the abstract adapter always returns false.

Returns:

  • (Boolean) 


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# File 'lib/active_record/connection_adapters/abstract_adapter.rb', line 55

def supports_migrations?
  false
end

#supports_primary_key? ⇒ Boolean

Can this adapter determine the primary key for tables not attached to an Active Record class, such as join tables? Backend specific, as the abstract adapter always returns false.

Returns:

  • (Boolean) 


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# File 'lib/active_record/connection_adapters/abstract_adapter.rb', line 62

def supports_primary_key?
  false
end

#supports_savepoints? ⇒ Boolean

Does this adapter support savepoints? PostgreSQL and MySQL do, SQLite does not.

Returns:

  • (Boolean) 


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# File 'lib/active_record/connection_adapters/abstract_adapter.rb', line 81

def supports_savepoints?
  false
end

#transaction_joinable=(joinable) ⇒ Object 



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# File 'lib/active_record/connection_adapters/abstract_adapter.rb', line 174

def transaction_joinable=(joinable)
  @transaction_joinable = joinable
end

#verify!(*ignored) ⇒ Object

Checks whether the connection to the database is still active (i.e. not stale). This is done under the hood by calling active?. If the connection is no longer active, then this method will reconnect to the database.



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# File 'lib/active_record/connection_adapters/abstract_adapter.rb', line 147

def verify!(*ignored)
  reconnect! unless active?
end