Object
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.
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.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 176 def active? @active != false end
Returns the human-readable name of the adapter. Use mixed case - one can always use downcase if needed.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 92 def adapter_name 'Abstract' end
# File 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
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 255 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.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 205 def clear_cache! # this should be overridden by concrete adapters end
Check the connection back in to the connection pool
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 268 def close pool.checkin self end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 246 def create_savepoint end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 263 def current_savepoint_name "active_record_#{open_transactions}" end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 238 def decrement_open_transactions @open_transactions -= 1 end
Override to turn off referential integrity while executing &block.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 167 def disable_referential_integrity yield end
Disconnects from the database if already connected. Otherwise, this method does nothing.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 188 def disconnect! @active = false end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 86 def expire @in_use = false end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 234 def increment_open_transactions @open_transactions += 1 end
# File 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
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.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 136 def prefetch_primary_key?(table_name = nil) false end
Override to return the quoted table name. Defaults to column quoting.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 154 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.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 228 def raw_connection @connection end
Disconnects from the database if already connected, and establishes a new connection with the database.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 182 def reconnect! @active = true end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 252 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.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 211 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.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 198 def reset! # this should be overridden by concrete adapters end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 249 def rollback_to_savepoint end
Returns a bind substitution value given a column and list of current binds
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 160 def substitute_at(column, index) Arel::Nodes::BindParam.new '?' end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 122 def supports_bulk_alter? false end
Does this adapter support using DISTINCT within COUNT? This is true for all adapters except sqlite.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 111 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.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 118 def supports_ddl_transactions? false end
Does this adapter support explain? As of this writing sqlite3, mysql2, and postgresql are the only ones that do.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 147 def supports_explain? false end
Does this adapter support index sort order?
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 141 def supports_index_sort_order? false end
Does this adapter support migrations? Backend specific, as the abstract adapter always returns false.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 98 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.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 105 def supports_primary_key? false end
Does this adapter support savepoints? PostgreSQL and MySQL do, SQLite < 3.6.8 does not.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 128 def supports_savepoints? false end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 242 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.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 218 def verify!(*ignored) reconnect! unless active? end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 274 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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