Class: ActiveRecord::ConnectionAdapters::AbstractAdapter

Inherits:
Object
  • Object
show all
Includes:
DatabaseLimits, DatabaseStatements, QueryCache, Quoting, SchemaStatements, ActiveSupport::Callbacks, MonitorMixin
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

Attributes included from QueryCache

#query_cache, #query_cache_enabled

Instance Method Summary collapse

Methods included from ActiveSupport::Callbacks

#run_callbacks

Methods included from ActiveSupport::Concern

#append_features, extended, #included

Methods included from QueryCache

#cache, #clear_query_cache, dirties_query_cache, #disable_query_cache!, #enable_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, #type_cast

Methods included from DatabaseStatements

#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 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, pool = nil) ⇒ AbstractAdapter

:nodoc:


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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 60

def initialize(connection, logger = nil, pool = nil) #:nodoc:
  super()

  @active              = nil
  @connection          = connection
  @in_use              = false
  @instrumenter        = ActiveSupport::Notifications.instrumenter
  @last_use            = false
  @logger              = logger
  @open_transactions   = 0
  @pool                = pool
  @query_cache         = Hash.new { |h,sql| h[sql] = {} }
  @query_cache_enabled = false
  @schema_cache        = SchemaCache.new self
  @visitor             = nil
end

Instance Attribute Details

#in_useObject (readonly) Also known as: in_use?

Returns the value of attribute in_use


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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 57

def in_use
  @in_use
end

#last_useObject (readonly)

Returns the value of attribute last_use


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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 57

def last_use
  @last_use
end

#loggerObject (readonly)

Returns the value of attribute logger


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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 57

def logger
  @logger
end

#open_transactionsObject (readonly)

Returns the value of attribute open_transactions


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

def open_transactions
  @open_transactions
end

#poolObject

Returns the value of attribute pool


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

def pool
  @pool
end

#schema_cacheObject (readonly)

Returns the value of attribute schema_cache


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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 57

def schema_cache
  @schema_cache
end

#visitorObject

Returns the value of attribute visitor


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

def visitor
  @visitor
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.


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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 176

def active?
  @active != false
end

#adapter_nameObject

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 92

def adapter_name
  'Abstract'
end

#case_insensitive_comparison(table, attribute, column, value) ⇒ Object


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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 259

def case_insensitive_comparison(table, attribute, column, value)
  table[attribute].lower.eq(table.lower(value))
end

#case_sensitive_modifier(node) ⇒ Object


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

def case_sensitive_modifier(node)
  node
end

#clear_cache!Object

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 205

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

#closeObject

Check the connection back in to the connection pool


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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 268

def close
  pool.checkin self
end

#create_savepointObject


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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 246

def create_savepoint
end

#current_savepoint_nameObject


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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 263

def current_savepoint_name
  "active_record_#{open_transactions}"
end

#decrement_open_transactionsObject


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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 238

def decrement_open_transactions
  @open_transactions -= 1
end

#disable_referential_integrityObject

Override to turn off referential integrity while executing &block.


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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 167

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

def disconnect!
  @active = false
end

#expireObject


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

def expire
  @in_use = false
end

#increment_open_transactionsObject


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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 234

def increment_open_transactions
  @open_transactions += 1
end

#leaseObject


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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 77

def lease
  synchronize do
    unless in_use
      @in_use   = true
      @last_use = Time.now
    end
  end
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.


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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 136

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 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 154

def quote_table_name(name)
  quote_column_name(name)
end

#raw_connectionObject

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 228

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 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 182

def reconnect!
  @active = true
end

#release_savepointObject


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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 252

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.


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

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

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

#rollback_to_savepointObject


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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 249

def rollback_to_savepoint
end

#substitute_at(column, index) ⇒ Object

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 160

def substitute_at(column, index)
  Arel::Nodes::BindParam.new '?'
end

#supports_bulk_alter?Boolean


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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 122

def supports_bulk_alter?
  false
end

#supports_count_distinct?Boolean

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 111

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.


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

def supports_ddl_transactions?
  false
end

#supports_explain?Boolean

Does this adapter support explain? As of this writing sqlite3, mysql2, and postgresql are the only ones that do.


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

def supports_explain?
  false
end

#supports_index_sort_order?Boolean

Does this adapter support index sort order?


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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 141

def supports_index_sort_order?
  false
end

#supports_migrations?Boolean

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 98

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.


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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 105

def supports_primary_key?
  false
end

#supports_savepoints?Boolean

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 128

def supports_savepoints?
  false
end

#transaction_joinable=(joinable) ⇒ Object


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# File 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 242

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 'activerecord/lib/active_record/connection_adapters/abstract_adapter.rb', line 218

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