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.
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- ActiveRecord::ConnectionAdapters::Quoting
- ActiveRecord::ConnectionAdapters::DatabaseStatements
- ActiveRecord::ConnectionAdapters::SchemaStatements
- ActiveRecord::ConnectionAdapters::DatabaseLimits
- ActiveRecord::ConnectionAdapters::QueryCache
- ActiveSupport::Callbacks
[RW] | visitor |
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
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
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 228 def case_sensitive_modifier(node) node end
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
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 219 def create_savepoint end
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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
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 211 def decrement_open_transactions @open_transactions -= 1 end
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
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
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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
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 202 def open_transactions @open_transactions ||= 0 end
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
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
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.
Source: show
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 198 def raw_connection @connection end
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
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 225 def release_savepoint end
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
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
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 222 def rollback_to_savepoint end
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
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 103 def supports_bulk_alter? false end
Does this adapter support using DISTINCT within COUNT? This is
true
for all adapters except sqlite.
Source: show
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 92 def supports_count_distinct? true end
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
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
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
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
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 215 def transaction_joinable=(joinable) @transaction_joinable = joinable end
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
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 238 def log(sql, name = "SQL", binds = []) @instrumenter.instrument( "sql.active_record", :sql => sql, :name => name, :connection_id => object_id, :binds => binds) { yield } rescue Exception => e message = "#{e.class.name}: #{e.message}: #{sql}" @logger.debug message if @logger exception = translate_exception(e, message) exception.set_backtrace e.backtrace raise exception end
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 253 def translate_exception(e, message) # override in derived class ActiveRecord::StatementInvalid.new(message) end