# class ActiveRecord::ConnectionAdapters::AbstractAdapter

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 SchemaStatements are very useful.

### Constants

ADAPTER_NAME
SIMPLE_INT

### Attributes

in_use?[R]
lock[R]
logger[R]
owner[R]
pool[RW]
prepared_statements[R]
schema_cache[R]
visitor[RW]

### Public Class Methods

type_cast_config_to_boolean(config) click to toggle source

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 88
    def self.type_cast_config_to_boolean(config)
      if config == "false"
        false
      else
        config
      end
    end

type_cast_config_to_integer(config) click to toggle source

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 80
    def self.type_cast_config_to_integer(config)
      if config =~ SIMPLE_INT
        config.to_i
      else
        config
      end
    end

### Public Instance Methods

active?() click to toggle source

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 396
    def active?
    end

adapter_name() click to toggle source

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 229
    def adapter_name
      self.class::ADAPTER_NAME
    end

clear_cache!() click to toggle source

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 427
    def clear_cache!
      # this should be overridden by concrete adapters
    end

close() click to toggle source

Check the connection back in to the connection pool

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 474
    def close
      pool.checkin self
    end

collector() click to toggle source

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 143
    def collector
      if prepared_statements
        SQLString.new
      else
        BindCollector.new
      end
    end

disable_extension(name) click to toggle source

This is meant to be implemented by the adapters that support extensions

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 353
    def disable_extension(name)
    end

disable_referential_integrity() { || ... } click to toggle source

Override to turn off referential integrity while executing `&block`.

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 387
    def disable_referential_integrity
      yield
    end

disconnect!() click to toggle source

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

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 409
    def disconnect!
      clear_cache!
      reset_transaction
    end

enable_extension(name) click to toggle source

This is meant to be implemented by the adapters that support extensions

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 357
    def enable_extension(name)
    end

expire() click to toggle source

this method must only be called while holding connection pool's mutex

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 193
    def expire
      if in_use?
        if @owner != Thread.current
          raise ActiveRecordError, "Cannot expire connection, "                "it is owned by a different thread: #{@owner}. "                "Current thread: #{Thread.current}."
        end

        @owner = nil
      else
        raise ActiveRecordError, "Cannot expire connection, it is not currently leased."
      end
    end

extensions() click to toggle source

A list of extensions, to be filled in by adapters that support them.

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 375
    def extensions
      []
    end

index_algorithms() click to toggle source

A list of index algorithms, to be filled by adapters that support them.

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 380
    def index_algorithms
      {}
    end

lease() click to toggle source

this method must only be called while holding connection pool's mutex

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 172
    def lease
      if in_use?
        msg = "Cannot lease connection, "
        if @owner == Thread.current
          msg << "it is already leased by the current thread."
        else
          msg << "it is already in use by a different thread: #{@owner}. "                     "Current thread: #{Thread.current}."
        end
        raise ActiveRecordError, msg
      end

      @owner = Thread.current
    end

prefetch_primary_key?(table_name = nil) click to toggle source

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.

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 266
    def prefetch_primary_key?(table_name = nil)
      false
    end

raw_connection() click to toggle source

Provides access to the underlying database driver for this adapter. For example, this method returns a Mysql2::Client object in case of Mysql2Adapter, and a PG::Connection 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 452
    def raw_connection
      @connection
    end

reconnect!() click to toggle source

Disconnects from the database if already connected, and establishes a new connection with the database. Implementors should call super if they override the default implementation.

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 402
    def reconnect!
      clear_cache!
      reset_transaction
    end

requires_reloading?() click to toggle source

Returns true if its required to reload the connection between requests for development mode.

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 432
    def requires_reloading?
      false
    end

reset!() click to toggle source

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 420
    def reset!
      # this should be overridden by concrete adapters
    end

schema_cache=(cache) click to toggle source

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 187
    def schema_cache=(cache)
      cache.connection = self
      @schema_cache = cache
    end

schema_creation() click to toggle source

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 159
    def schema_creation
      SchemaCreation.new self
    end

supports_advisory_locks?() click to toggle source

Does this adapter support application-enforced advisory locking?

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 259
    def supports_advisory_locks?
      false
    end

supports_bulk_alter?() click to toggle source

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 249
    def supports_bulk_alter?
      false
    end

supports_comments?() click to toggle source

Does this adapter support metadata comments on database objects (tables, columns, indexes)?

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 333
    def supports_comments?
      false
    end

supports_comments_in_create?() click to toggle source

Can comments for tables, columns, and indexes be specified in create/alter table statements?

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 338
    def supports_comments_in_create?
      false
    end

supports_datetime_with_precision?() click to toggle source

Does this adapter support datetime with precision?

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 323
    def supports_datetime_with_precision?
      false
    end

supports_ddl_transactions?() click to toggle source

Does this adapter support DDL rollbacks in transactions? That is, would CREATE TABLE or ALTER TABLE get rolled back by a transaction?

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 245
    def supports_ddl_transactions?
      false
    end

supports_explain?() click to toggle source

Does this adapter support explain?

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 286
    def supports_explain?
      false
    end

supports_expression_index?() click to toggle source

Does this adapter support expression indices?

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 281
    def supports_expression_index?
      false
    end

supports_extensions?() click to toggle source

Does this adapter support database extensions?

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 296
    def supports_extensions?
      false
    end

supports_foreign_keys?() click to toggle source

Does this adapter support creating foreign key constraints?

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 307
    def supports_foreign_keys?
      false
    end

supports_foreign_keys_in_create?() click to toggle source

Does this adapter support creating foreign key constraints in the same statement as creating the table?

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 313
    def supports_foreign_keys_in_create?
      supports_foreign_keys?
    end

supports_index_sort_order?() click to toggle source

Does this adapter support index sort order?

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 271
    def supports_index_sort_order?
      false
    end

supports_indexes_in_create?() click to toggle source

Does this adapter support creating indexes in the same statement as creating the table?

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 302
    def supports_indexes_in_create?
      false
    end

supports_json?() click to toggle source

Does this adapter support json data type?

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 328
    def supports_json?
      false
    end

supports_multi_insert?() click to toggle source

Does this adapter support multi-value insert?

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 343
    def supports_multi_insert?
      true
    end

supports_partial_index?() click to toggle source

Does this adapter support partial indices?

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 276
    def supports_partial_index?
      false
    end

supports_savepoints?() click to toggle source

Does this adapter support savepoints?

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 254
    def supports_savepoints?
      false
    end

supports_transaction_isolation?() click to toggle source

Does this adapter support setting the isolation level for a transaction?

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 291
    def supports_transaction_isolation?
      false
    end

supports_views?() click to toggle source

Does this adapter support views?

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 318
    def supports_views?
      false
    end

supports_virtual_columns?() click to toggle source

Does this adapter support virtual columns?

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 348
    def supports_virtual_columns?
      false
    end

unprepared_statement() { || ... } click to toggle source

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 220
    def unprepared_statement
      old_prepared_statements, @prepared_statements = @prepared_statements, false
      yield
    ensure
      @prepared_statements = old_prepared_statements
    end

verify!(*ignored) click to toggle source

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 439
    def verify!(*ignored)
      if ignored.size > 0
        ActiveSupport::Deprecation.warn("Passing arguments to #verify method of the connection has no effect and has been deprecated. Please remove all arguments from the #verify method call.")
      end
      reconnect! unless active?
    end

### Private Instance Methods

can_perform_case_insensitive_comparison_for?(column) click to toggle source

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 468
    def can_perform_case_insensitive_comparison_for?(column)
      true
    end

column_for(table_name, column_name) click to toggle source

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 633
    def column_for(table_name, column_name)
      column_name = column_name.to_s
      columns(table_name).detect { |c| c.name == column_name } ||
        raise(ActiveRecordError, "No such column: #{table_name}.#{column_name}")
    end

extract_limit(sql_type) click to toggle source

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 581
    def extract_limit(sql_type)
      case sql_type
      when /^bigint/i
        8
      when /\((.*)\)/
        $1.to_i
      end
    end

extract_precision(sql_type) click to toggle source

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 577
    def extract_precision(sql_type)
      $1.to_i if sql_type =~ /\((\d+)(,\d+)?\)/
    end

extract_scale(sql_type) click to toggle source

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 570
    def extract_scale(sql_type)
      case sql_type
      when /\((\d+)\)/ then 0
      when /\((\d+)(,(\d+))\)/ then $3.to_i
      end
    end

initialize_type_map(m) click to toggle source

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 520
    def initialize_type_map(m)
      register_class_with_limit m, %r(boolean)i,       Type::Boolean
      register_class_with_limit m, %r(char)i,          Type::String
      register_class_with_limit m, %r(binary)i,        Type::Binary
      register_class_with_limit m, %r(text)i,          Type::Text
      register_class_with_precision m, %r(date)i,      Type::Date
      register_class_with_precision m, %r(time)i,      Type::Time
      register_class_with_precision m, %r(datetime)i,  Type::DateTime
      register_class_with_limit m, %r(float)i,         Type::Float
      register_class_with_limit m, %r(int)i,           Type::Integer

      m.alias_type %r(blob)i,      "binary"
      m.alias_type %r(clob)i,      "text"
      m.alias_type %r(timestamp)i, "datetime"
      m.alias_type %r(numeric)i,   "decimal"
      m.alias_type %r(number)i,    "decimal"
      m.alias_type %r(double)i,    "float"

      m.register_type(%r(decimal)i) do |sql_type|
        scale = extract_scale(sql_type)
        precision = extract_precision(sql_type)

        if scale == 0
          # FIXME: Remove this class as well
          Type::DecimalWithoutScale.new(precision: precision)
        else
          Type::Decimal.new(precision: precision, scale: scale)
        end
      end
    end

log(sql, name = "SQL", binds = [], type_casted_binds = [], statement_name = nil) { || ... } click to toggle source

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 602
    def log(sql, name = "SQL", binds = [], type_casted_binds = [], statement_name = nil) # :doc:
      @instrumenter.instrument(
        "sql.active_record",
        sql:               sql,
        name:              name,
        binds:             binds,
        type_casted_binds: type_casted_binds,
        statement_name:    statement_name,
        connection_id:     object_id) do
          @lock.synchronize do
            yield
          end
        end
    rescue => e
      raise translate_exception_class(e, sql)
    end

register_class_with_limit(mapping, key, klass) click to toggle source

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 556
    def register_class_with_limit(mapping, key, klass)
      mapping.register_type(key) do |*args|
        limit = extract_limit(args.last)
        klass.new(limit: limit)
      end
    end

register_class_with_precision(mapping, key, klass) click to toggle source

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 563
    def register_class_with_precision(mapping, key, klass)
      mapping.register_type(key) do |*args|
        precision = extract_precision(args.last)
        klass.new(precision: precision)
      end
    end

reload_type_map() click to toggle source

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 551
    def reload_type_map
      type_map.clear
      initialize_type_map(type_map)
    end

translate_exception(exception, message) click to toggle source

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 619
    def translate_exception(exception, message)
      # override in derived class
      case exception
      when RuntimeError
        exception
      else
        ActiveRecord::StatementInvalid.new(message)
      end
    end

translate_exception_class(e, sql) click to toggle source

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 590
    def translate_exception_class(e, sql)
      begin
        message = "#{e.class.name}: #{e.message}: #{sql}"
      rescue Encoding::CompatibilityError
        message = "#{e.class.name}: #{e.message.force_encoding sql.encoding}: #{sql}"
      end

      exception = translate_exception(e, message)
      exception.set_backtrace e.backtrace
      exception
    end

without_prepared_statement?(binds) click to toggle source

    # File lib/active_record/connection_adapters/abstract_adapter.rb, line 629
    def without_prepared_statement?(binds)
      !prepared_statements || binds.empty?
    end