New Features

• Dataset#first! has been added. This is identical to first, except where first would return nil due to no row matching, first! raises a Sequel::NoMatchingRow exception. The main benefit here is that a standard exception class is now used, so external libraries can deal with these exceptions appropriately (such as web applications returning a 404 error).
• Dataset#with_pk! has been added to model datasets. Similar to first!, this raises a Sequel::NoMatchingRow exception instead of returning nil if there is no matching row.
• A drop_foreign_key method has been added to the alter_table generator:

    alter_table(:tab){drop_foreign_key :col}
  

  This relies on foreign_key_list working and including the name of the foreign key. Previously, you‘d have to drop the foreign key constraint before dropping the column in some cases.

• Column constraints can now be named using :*_constraint_name options:

    create_table(:tab) do
      primary_key :id, :primary_key_constraint_name=>:pk_name
      foriegn_key :t_id, :t, :foreign_key_constraint_name=>:fk_name,
        :unique=>true, :unique_constraint_name=>:uk_name
    end
  

  This makes it easier to name constraints, which has always been recommended as it makes it easier to drop such constraints in the future.

• On Microsoft SQL Server, Dataset#cross_apply and outer_apply have been added to use CROSS/OUTER APPLY. These are useful if you want to join a table to the output of a function that takes the table as an argument.

Other Improvements

• The connection pools are now faster when using the :connection_handling=>:queue option.
• External connection pool classes can now be loaded automatically by the :pool_class option.
• Database#each_server now raises if not given a block. Previously, it just leaked Database references.
• On Microsoft SQL Server, ] characters are now escaped correctly in identifiers.
• On PostgreSQL, infinite dates are also handled when using Database#convert_infinite_timestamps. Previously, infinite dates were incorrectly converted to 0000-01-01.
• The associations, composition, serialization, and dirty plugins now clear caches stored in the instance in some additional cases, such as when saving model instances when the dataset supports insert_select.
• Model#validates_type in the validation_helpers plugin now handles false values correctly.
• The string_stripper plugin has been fixed to not change the result of Model.set_dataset.
• You can now drop primary key constraints on H2, using:

    alter_table(:tab){drop_constraint :foo, :type=>:primary_key}
  

• The jdbc/as400 adapter has been fixed, it was broken starting in Sequel 3.44.0.
• A Security guide has been added explaining various security issues to think about when using Sequel.

Backwards Compatibility

• The change to make associations, composition, serialization, and dirty now clear caches after saving when the dataset supports insert_select can break code that expected the previous behavior. For example:

    artist = Artist[1]
    artist.has_albums # => false
  
    album = Album.new(:artist=>artist)
    def album.after_create
      super
      artist.update(:has_albums=>true)
    end
    album.save
  
    artist.has_albums # => false
  

  Such code should either refresh the artist after saving the album, or use album.artist.has_albums. You already had to do that if the dataset did not support insert_select; the impetus for this change was to make the behavior consistent.

• Decimal/numeric columns are now strictly typecast by default, similar to integer and real/double precision columns. If you want the previous loose typecasting to for decimal/numeric columns, use the looser_typecasting extension.
• External adapters that called Database.set_adapter_scheme with a string should change to using a symbol.
• Dataset#select_map, select_order_map, and get now raise an exception if they are passed a plain string inside an array. If you do want to use a plain string, you now need to alias it:

    dataset.get([Sequel.as('string', :some_alias)])
  

Sequel 4 Implementation Planning

• Sequel 4 implementation planning has begun. If you want to view and/or provide feedback on the implementation plan, see github.com/jeremyevans/sequel-4-plans