5.12.0.txt

doc/release_notes/5.12.0.txt
Last Update: 2018-08-31 08:39:42 -0700

New Features

  • An eager_graph_eager plugin has been added, which allows you to chain eager loads using separate queries to an existing dataset that uses eager_graph. Given the following model associations:

    Band.one_to_many :albums
    Album.one_to_many :tracks

    Let's say you wanted to return bands ordered by album name, and eagerly load those albums, you can do that using:

    Band.eager_graph(:albums).order{albums[:name]}

    Let's say you also wanted to eagerly load the tracks for each album. You could just add them to the eager_graph call:

    Band.eager_graph(albums: :tracks).order{albums[:name]}

    However, the bloats the result set, and you aren't ordering by the track information, so a join is not required. The eager_graph_eager plugin allows you to specify that the tracks be eagerly loaded in a separate query after the eager_graph load of albums:

    Band.eager_graph(:albums).
      eager_graph_eager([:albums], :tracks).
      order{albums[:name]}

    eager_graph_eager's first argument is a dependency chain, specified as an array of symbols. This specifies the point at which to perform the eager load. The remaining arguments are arguments that could be passed to Dataset#eager to specify what dependent associations should be loaded at that point.

  • A caller_logging Database extension has been added, which logs caller information before queries, filtering out the internal Sequel callers. Example:

    DB.extension :caller_logging
    DB[:table].first
    # Logger:
    # (0.000041s) (source: /path/to/app/foo/t.rb:12 in `get_first`)
    # SELECT * FROM table LIMIT 1

    You can further filter the caller lines by setting Database#caller_logging_ignore to a regexp of additional caller lines to ignore. This is useful if you have specific methods or internal extensions/plugins that you would also like to ignore as they obscure the code actually making the request.

    DB.caller_logging_ignore = %r{/path/to/app/lib/plugins}

    You can also format the caller before it is placed in the logger, using caller_logging_formatter:

    DB.caller_logging_formatter = lambda do |caller|
      "(#{caller.sub(/\A\/path\/to\/app\//, '')})"
    end
    DB[:table].first
    # Logger:
    # (0.000041s) (foo/t.rb:12 in `get_first`) SELECT * FROM table LIMIT 1
  • Database#call_procedure has been added to the postgres adapter, and is usable on PostgreSQL 11+ for calling procedures created with CREATE PROCEDURE.

    DB.call_procedure(:foo, 1, "bar")
    # CALL foo(1, 'bar')

    This method will return a hash of results if the procedure returns a result, or nil if it does not return a result.

Other Improvements

  • It is now possible to use Dataset#eager_graph in an eager load callback for associations that use join tables. This allows you to eager load some associations using separate queries and other associations using joins. For example:

    Band.eager(:albums=>proc{|ds| ds.eager_graph(:tracks)})

    Will load the bands in one query, and load the albums and tracks in a separate query using a join. Previously, this construction worked only for associations that did not use join tables. It now works for associations that use join tables, as long as existing selected columns are not removed inside the callback.

  • The tactical_eager_loading plugin now handles automatic eager loading for associated objects that were created during the load of dataset that uses eager_graph. When using the plugin, the following code will now only execute 2 queries, instead of issuing a separate query for each album to get the tracks for the album.

    artists = Artist.eager_graph(:albums).all
    artists.each do |artist|
      artist.albums.each do |album|
        album.tracks
      end
    end
  • Calling Dataset#graph with a dataset with existing selections where the column aliases cannot be determined automatically now works correctly by using a subselect. Previously, attempting to do this would raise an exception. This allows the following code to work:

    DB[:table].select_all(:table).select_append(expr).graph(...)
  • Datasets now cache the EagerGraphLoader object that is generated to convert arrays of hashes into an object graph, so that subsequent eager loads on the same dataset do not need to recompute the same information. Most EagerGraphLoader internal state is now frozen to prevent unintentional modification.

  • Sequel.extension now loads files from gems. Previously, it used Kernel.require, which does not load files from gems.

  • Adapters that emulate prepared statements using literalization now use a placeholder literalizer and should execute significantly faster. More prepared statement internal metadata is now frozen to prevent unintentional modification.

  • Dataset#intersect, except, and nowait are now supported on MariaDB 10.3+.

  • The constraint_validations extension now respects the constraint_validations_table setting when adding metadata for the constraint validations.

  • In the oracle adapter, the clob prepared statement argument type is now mapped to the OCI8::CLOB class, allowing the use of Oracle procedures with clob output parameters.

  • The Model.load_cache method in the static_cache plugin is now public.

Backwards Compatibility

  • The private Dataset#prepared_arg? method has been removed. It is no longer necessary after the refactoring to the prepared statement code. External adapters that currently call the method should be updated to no longer call the method.