Class: ActiveRecord::ConnectionAdapters::AbstractAdapter

Inherits:
Object
  • Object
show all
Includes:
DatabaseLimits, DatabaseStatements, Quoting, SchemaStatements, QueryCache, ActiveSupport::Callbacks
Defined in:
activerecord/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.

Instance Attribute Summary (collapse)

Class Method Summary (collapse)

Instance Method Summary (collapse)

Methods included from ActiveSupport::Callbacks

#run_callbacks

Methods included from ActiveSupport::Concern

#append_features, extended, #included

Methods inherited from QueryCache

#call

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 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

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, #exec_delete, #exec_insert, #exec_query, #exec_update, #execute, #insert, #insert_fixture, #join_to_update, #limited_update_conditions, #outside_transaction?, #reset_sequence!, #rollback_db_transaction, #sanitize_limit, #select_all, #select_one, #select_rows, #select_value, #select_values, #supports_statement_cache?, #to_sql, #transaction, #update

Methods included from Quoting

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

Constructor Details

- (AbstractAdapter) initialize(connection, logger = nil)

:nodoc:



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 44

def initialize(connection, logger = nil) #:nodoc:
  @active = nil
  @connection, @logger = connection, logger
  @query_cache_enabled = false
  @query_cache = Hash.new { |h,sql| h[sql] = {} }
  @instrumenter = ActiveSupport::Notifications.instrumenter
  @visitor = nil
end

Instance Attribute Details

- (Object) visitor

Returns the value of attribute visitor



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 42

def visitor
  @visitor
end

Class Method Details

+ (Object) visitor_for(pool)

Returns a visitor instance for this adaptor, which conforms to the Arel::ToSql interface



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 54

def self.visitor_for(pool) # :nodoc:
  adapter = pool.spec.config[:adapter]

  if Arel::Visitors::VISITORS[adapter]
    ActiveSupport::Deprecation.warn(
      "Arel::Visitors::VISITORS is deprecated and will be removed. Database adapters " \
      "should define a visitor_for method which returns the appropriate visitor for " \
      "the database. For example, MysqlAdapter.visitor_for(pool) returns " \
      "Arel::Visitors::MySQL.new(pool)."
    )

    Arel::Visitors::VISITORS[adapter].new(pool)
  else
    Arel::Visitors::ToSql.new(pool)
  end
end

Instance Method Details

- (Boolean) active?

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.



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 146

def active?
  @active != false
end

- (Object) adapter_name

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



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 73

def adapter_name
  'Abstract'
end

- (Object) case_sensitive_modifier(node)



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 228

def case_sensitive_modifier(node)
  node
end

- (Object) clear_cache!

Clear any caching the database adapter may be doing, for example clearing the prepared statement cache. This is database specific.



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 175

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

- (Object) create_savepoint



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 219

def create_savepoint
end

- (Object) current_savepoint_name



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 232

def current_savepoint_name
  "active_record_#{open_transactions}"
end

- (Object) decrement_open_transactions



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 211

def decrement_open_transactions
  @open_transactions -= 1
end

- (Object) disable_referential_integrity

Override to turn off referential integrity while executing &block.



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 137

def disable_referential_integrity
  yield
end

- (Object) disconnect!

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



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 158

def disconnect!
  @active = false
end

- (Object) increment_open_transactions



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 206

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

- (Object) open_transactions



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 202

def open_transactions
  @open_transactions ||= 0
end

- (Boolean) prefetch_primary_key?(table_name = nil)

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.



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 117

def prefetch_primary_key?(table_name = nil)
  false
end

- (Object) quote_table_name(name)

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



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

def quote_table_name(name)
  quote_column_name(name)
end

- (Object) raw_connection

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 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 198

def raw_connection
  @connection
end

- (Object) reconnect!

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



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 152

def reconnect!
  @active = true
end

- (Object) release_savepoint



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 225

def release_savepoint
end

- (Boolean) requires_reloading?

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.



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

def requires_reloading?
  false
end

- (Object) reset!

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 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 168

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

- (Object) rollback_to_savepoint



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 222

def rollback_to_savepoint
end

- (Object) substitute_at(column, index)

Returns a bind substitution value given a column and list of current binds



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 130

def substitute_at(column, index)
  Arel.sql '?'
end

- (Boolean) supports_bulk_alter?



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

def supports_bulk_alter?
  false
end

- (Boolean) supports_count_distinct?

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



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 92

def supports_count_distinct?
  true
end

- (Boolean) supports_ddl_transactions?

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.



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 99

def supports_ddl_transactions?
  false
end

- (Boolean) supports_migrations?

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



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 79

def supports_migrations?
  false
end

- (Boolean) supports_primary_key?

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.



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 86

def supports_primary_key?
  false
end

- (Boolean) supports_savepoints?

Does this adapter support savepoints? PostgreSQL and MySQL do, SQLite < 3.6.8 does not.



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 109

def supports_savepoints?
  false
end

- (Object) transaction_joinable=(joinable)



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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 215

def transaction_joinable=(joinable)
  @transaction_joinable = joinable
end

- (Object) verify!(*ignored)

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 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 188

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