New Plugins
-----------

* A class_table_inheritance plugin has been added, supporting model
  inheritance in the database using a table-per-model-class approach.
  Each table stores only attributes unique to that model or subclass
  hierarchy.
  
  For example, with this hierarchy:

                Employee
               /        \
            Staff     Manager
                         |
                      Executive

  the following database schema may be used (table - columns):

  * employees - id, name, kind
  * staff - id, manager_id
  * managers - id, num_staff
  * executives - id, num_managers

  The class_table_inheritance plugin assumes that the main table
  (e.g. employees) has a primary key field (usually
  autoincrementing), and all other tables have a foreign key of the
  same name that points to the same key in their superclass's table.
  For example:

  * employees.id  - primary key, autoincrementing
  * staff.id - foreign key referencing employees(id)
  * managers.id - foreign key referencing employees(id)
  * executives.id - foreign key referencing managers(id)

  When using the class_table_inheritance plugin, subclasses use joined
  datasets:

    Employee.dataset.sql  # SELECT * FROM employees
    Manager.dataset.sql   # SELECT * FROM employees
                          # INNER JOIN managers USING (id)
    Executive.dataset.sql # SELECT * FROM employees
                          # INNER JOIN managers USING (id)
                          # INNER JOIN executives USING (id)

  This allows Executive.all to return instances with all attributes
  loaded.  The plugin overrides deleting, inserting, and updating
  in the model to work with multiple tables, by handling each table
  individually.

  This plugin allows and encourages the use of a :key option to mark
  a column holding the class name.  This allows methods on the
  superclass to return instances of specific subclasses.

    a = Employee.all # [<#Staff>, <#Manager>, <#Executive>]
    
  This plugin requires the lazy_attributes plugin and uses it to
  handle subclass specific attributes that would not be loaded
  when calling superclass methods (since those wouldn't join
  to the subclass tables).  For example:
    
    a.first.values # {:id=>1, name=>'S', :kind=>'Staff'}
    a.first.manager_id # Loads the manager_id attribute from the
                       # database
                       
  The class_table_inheritance plugin requires JOIN USING and
  therefore is not supported on H2 or Microsoft SQL Server, which do
  not support that SQL-92 feature.
  
* An associations_dependencies plugin was added for deleting,
  destroying, or nullifying associated objects when destroying a
  model object.  This just gives an easy way to add the necessary
  before and after destroy hooks.  The following association types
  support the following dependency actions:

  * :many_to_many - :nullify (removes all related entries in join
    table)
  * :many_to_one - :delete, :destroy
  * :one_to_many - :delete, :destroy, :nullify (sets foreign key to
    NULL for all associated objects)
    
  This plugin works directly with the association datasets and does
  not use any cached association values.  The :delete action will
  delete all associated objects from the database in a single SQL
  call. The :destroy action will load each associated object from the
  database and call the destroy method on it.
  
  The plugin call takes a hash of association symbol keys and 
  dependency action symbol values.  Alternatively, you can specify
  additional dependencies later using add_association_dependencies:
  
    Business.plugin :association_dependencies, :address=>:delete
    # or:
    Artist.plugin :association_dependencies
    Artist.add_association_dependencies :albums=>:destroy,
      :reviews=>:delete, :tags=>:nullify

* A force_encoding plugin was added that forces the encoding of
  strings used in model instances.  When model instances are loaded
  from the database, all values in the hash that are strings are
  forced to the given encoding.  Whenever you update a model column
  attribute, the resulting value is forced to a given encoding if the
  value is a string.  There are two ways to specify the encoding.
  You can either do so in the plugin call itself, or via the
  forced_encoding class accessor:
  
    class Album < Sequel::Model
      plugin :force_encoding, 'UTF-8'
      # or
      plugin :force_encoding
      self.forced_encoding = 'UTF-8'
    end
    
  This plugin only works on ruby 1.9, since strings don't have
  encodings in 1.8.
  
* A typecast_on_load plugin was added, for fixing bad database
  typecasting when loading model objects. Most of Sequel's database
  adapters don't have complete control over typecasting, and may
  return columns that aren't typecast correctly (with correct being
  defined as how the model object would typecast the same column
  values).

  This plugin modifies Model.load to call the setter methods (which
  typecast by default) for all columns given.  You can either specify
  the columns to typecast on load in the plugin call itself, or
  afterwards using add_typecast_on_load_columns:

    Album.plugin :typecast_on_load, :release_date, :record_date
    # or:
    Album.plugin :typecast_on_load
    Album.add_typecast_on_load_columns :release_date, :record_date

  If the database returns release_date and record_date columns as
  strings instead of dates, this will ensure that if you access those
  columns through the model object, you'll get Date objects instead of
  strings.

* A touch plugin was added, which adds Model#touch for updating an
  instance's timestamp, as well as touching associations when an
  instance is updated or destroyed.
  
  The Model#touch instance method saves the object with a modified
  timestamp.  By default, it uses the :updated_at column, but you can
  set which column to use. It also supports touching of associations,
  so that when the current model object is updated or destroyed, the
  associated rows in the database can have their modified timestamp
  updated to the current timestamp.  Example:
  
    class Album < Sequel::Model
      plugin :touch, :column=>:modified_on, :associations=>:artist
    end

* A subclasses plugin was added, for recording all of a models
  subclasses and descendent classes.  Direct subclasses are available
  via the subclasses method, and all descendent classes are available
  via the descendents method:

    c = Class.new(Sequel::Model)
    c.plugin :subclasses
    sc1 = Class.new(c)
    sc2 = Class.new(c)
    ssc1 = Class.new(sc1)
    c.subclasses    # [sc1, sc2]
    sc1.subclasses  # [ssc1]
    sc2.subclasses  # []
    ssc1.subclasses # []
    c.descendents   # [sc1, ssc1, sc2]

  The main use case for this is if you want to modify all models
  after the model subclasses have been created.  Since mutable
  options are copied when subclassing, modifying parent classes
  does not affect current subclasses, only future ones.  The
  subclasses plugin allows you get all subclasses so that you can
  easily modify them.  The plugin only records subclasses
  created after the plugin call, though.

* An active_model plugin was added, giving Sequel::Model an
  ActiveModel complaint API, in so much as it passes the
  ActiveModel::Lint tests.

New Extensions
--------------

* A named_timezones extension was added, allowing you to use named
  timezones such as "America/Los_Angeles" (the default Sequel
  timezone support only supports UTC or local time). This extension
  requires TZInfo.  It also sets the Sequel.datetime_class to 
  DateTime, so database timestamps will be returned as DateTime
  instances instead of Time instances.  This is because ruby's
  Time class doesn't support timezones other than UTC and local time.
  
  This plugin allows you to pass either strings or TZInfo::Timezone
  instance to Sequel.database_timezone=, application_timezone=, and
  typecast_timezone=.  If a string is passed, it is converted to a
  TZInfo::Timezone using TZInfo::Timezone.get.

  Let's say you have the database server in New York and the
  application server in Los Angeles.  For historical reasons, data
  is stored in local New York time, but the application server only
  services clients in Los Angeles, so you want to use New York
  time in the database and Los Angeles time in the application.  This
  is easily done via:

    Sequel.database_timezone = 'America/New_York'
    Sequel.application_timezone = 'America/Los_Angeles'

  Then, before timestamps are stored in the database, they are
  converted to New York time.  When timestamps are retrieved from the
  database, they are converted to Los Angeles time.

* A thread_local_timezones extension was added.  This allows you to
  set a per-thread timezone that will override the default global
  timezone while the thread is executing.  The main use case is for
  web applications that execute each request in its own thread, and
  want to set the timezones based on the request.  The most common
  example is having the database always store time in UTC, but have
  the application deal with the timezone of the current user.  That
  can be done with:
  
    Sequel.database_timezone = :utc
    # In each thread:
    Sequel.thread_application_timezone = current_user.timezone

  This extension is designed to work with the named_timezones
  extension.
  
* An sql_expr extension was added that adds .sql_expr methods to
  all objects, giving them easy access to Sequel's DSL:
  
    1.sql_expr < :a     # 1 < a
    false.sql_expr & :a # FALSE AND a
    true.sql_expr | :a  # TRUE OR a
    ~nil.sql_expr       # NOT NULL
    "a".sql_expr + "b"  # 'a' || 'b'

  Proc#sql_expr uses a virtual row:

    proc{[[a, b], [a, c]]}.sql_expr | :x
    # (((a = b) AND (a = c)) OR x)

* A looser_typecasting extension was added, for using to_f and to_i
  instead of the more strict Kernel.Float and Kernel.Integer when
  typecasting floats and integers. To use it, you should extend the
  database with the Sequel::LooserTypecasting module after loading
  the extension:

    Sequel.extension :looser_typecasting
    DB.extend(Sequel::LooserTypecasting)

  This makes the behavior more like ActiveRecord:
  
    a = Artist.new(:num_albums=>'a')
    a.num_albums # => 0

Other New Features
------------------

* Associations now support composite keys.  All of the :*key options
  options now accept arrays of symbols instead of plain symbols.
  Example:
  
    Artist.primary_key # [:name, :city]
    Album.many_to_one :artist, :key=>[:artist_name, :artist_city]
    Artist.one_to_many :albums, :key=>[:artist_name, :artist_city]
    
  All association types are supported, including the built-in
  many_to_many association and the many_through_many plugin.  Both
  methods of eager loading work with composite keys for all
  association types. Setter and add/remove/remove_all methods
  also now work with composite keys.
  
* Associations now respect a :validate option, which can be set to
  false to not validate when implicitly saving associated objects.
  
  There isn't a lot of implicit saving in Sequel's association
  methods, but this gives the user the control over validation when
  the association methods implicitly save an object.

* In addition to the regular association methods, the
  nested_attributes plugin was also updated to respect the
  :validate_association option. It was also modified to not validate
  associated objects twice, once when the parent object was validated
  and again when the associated object was saved.  Additionally, if
  you pass :validate=>false to the save method when saving the parent
  object, it will not longer attempt to validate associated objects
  when saving them.

* Dataset#insert and #insert_sql were refactored and now support the
  following API:
  
  * No arguments - Treat as a single empty hash argument
  * Single argument:
    * Hash - Use keys as columns and values as values
    * Array - Use as values, without specifying columns
    * Dataset - Use a subselect, without specifying columns
    * LiteralString - Use as the values
  * 2 arguments:
    * Array, Array - Use first array as keys, second as values
    * Array, Dataset - Use a subselect, with the array as columns
    * Array, LiteralString - Use LiteralString as the values, with
      the array as the columns
  * Anything else: Treat all given values an an array of values

* Graphing now works with previously joined datasets.  The main use
  case of this is when eagerly loading (via eager_graph) model
  associations for models backed by joined datasets, such as those
  created by the class_table_inheritance plugin.
  
* Sequel.virtual_row was added allowing you to easily use the
  VirtualRow support outside of select, order, and filter calls:
  
    net_benefit = Sequel.virtual_row{revenue > cost}
    good_employee = Sequel.virtual_row{num_commendations > 0}
    fire = ~net_benefit & ~good_employee
    demote = ~net_benefit & good_employee
    promote = net_benefit & good_employee
    DB[:employees].filter(fire).update(:employed=>false)
    DB[:employees].filter(demote).update(:rank=>:rank-1)
    DB[:employees].filter(promote).update(:rank=>:rank+1)

* When Sequel wraps exception in its own classes (to provide database
  independence), it now keeps the wrapped exception available in
  a wrapped_exception accessor.  This allows you to more easily
  determine the wrapped exception class, without resorting to parsing
  the exception message.
  
    begin
      DB.run('...')
    rescue Sequel::DatabaseError => e
      case e.wrapped_exception
      when Mysql::Error
        ...
      when PGError
        ...
      end
    end
    
* The MySQL adapter now supports a Dataset#split_multiple_result_sets
  method that yields arrays of rows (one per result set), instead of
  rows.  This allows you to submit multiple statements at the same
  time (or call a stored procedure that returns multiple result
  sets), and know which rows are related to which result sets.
  
  This violates a lot of Sequel's internal assumptions and should be
  used with care.  Existing row_procs are modified to work correctly,
  but graphing will not work on these datasets.

* The ADO adapter now accepts a :conn_string option and uses that
  as the full ADO connection string.  This can be used to connect to
  any datasource ADO supports, such as Microsoft Excel.
  
* The Microsoft SQL Server shared adapter now supports a
  Database#server_version method.
  
* The Microsoft SQL Server shared adapter now supports updating and
  deleting from joined datasets.
  
* The Microsoft SQL Server shared adapter now supports a
  Dataset#output method that uses the OUTPUT clause.

* Model#_save now calls either Model#_insert or Model#_update for
  inserting/updating the row in the database.  This allows for easier
  overriding when you want to allow creating and updating model
  objects backed by a joined dataset.
  
* Dataset#graph now takes a :from_self_alias option specifying the
  alias to use for the subselect created if the receiver is a joined
  but not yet graphed dataset.  It defaults to the first source table
  in the receiver.

Other Improvements
------------------

* Typecasting model attributes is now done before checking existing
  values, instead of after.  Before, the code for the model attribute
  setters would compare the given value to the existing entry.  If it
  didn't match, the value was typecasted and then assigned.  That led
  to the following situation:

    a = Album[1]
    a.num_tracks # => 10
    params # => {'num_tracks'=>'10'}
    a.set(params)
    a.changed_columns # => [:num_tracks]

  The new behavior typecasts the value first, and only sets it and
  records the column as changed if it doesn't match the typecasted
  value.
  
* Model#modified? is now always true if the record is new.  modified?
  indicates the instance's status relative to the database, and since
  a new object is not yet in the database, and saving the object
  would add it, the object is considered modified. A consequence of
  this is that Model#save_changes now always saves if the object is
  new.
  
  If you want to check if there were changes to columns since the
  object was first initialized, you should use
  !changed_columns.empty?, which was the historical way to handle
  the situation.

* The DataObjects (do) adpater now supports DataObjects 0.10.

* Dataset#select_more and Dataset#order_more no longer affect the
  receiver.  They are supposed to just return a modified copy of the
  receiver instead of modifying the receiver itself.  For a few
  versions they have been broken in that they modified the receiver
  in addition to returning a modified copy.
  
* Performance was increased for execution of prepared statements
  with multiple bound variables on MySQL.
  
* On MySQL, database errors raised when preparing statements or
  setting bound variable values are now caught and raised as
  Sequel::DatabaseErrors.
  
* On MySQL, more types of disconnection errors are detected.
  
* When altering columns in MySQL, options such as :unsigned,
  :elements, and :size that are given in the call are now respected.

* MySQL enum defaults are now handled correctly in the schema dumper.

* The schema dumper no longer attempts to use unparseable defaults
  as literals on MySQL, since MySQL does not provide defaults as
  valid literals.

* The emulated offset support in the shared Microsoft SQL Server
  adapter now works better with model classes (or any datasets with
  row_procs).
  
* Microsoft SQL Server now supports using the WITH clause in delete,
  update, and insert calls.
  
* Parsed indexes when connecting to Microsoft SQL Server via JDBC no
  longer include primary key indexes.
  
* Dataset#insert_select now returns nil if disable_insert_returning
  is used in the shared PostgreSQL adapter.  This makes it work as
  expected with model object creation.
  
* Calling Model.set_primary_key with an array of symbols to set
  a composite primary key is now supported.  You can also provide
  multiple symbol arguments to do the same thing.  Before, specifying
  an array of symbols broke the Model.[] optimization.

* Literalization of timezones in timestamps now works correctly on
  Oracle.
  
* __FILE__ and __LINE__ are now used everywhere that eval is called
  with a string, which makes for better backtraces.
  
* The native MySQL adapter now correctly handles returning before
  yielding all result sets.  Previously, this caused a commands out
  of sync error.
  
* Table names in common table expressions are now quoted.

* The Oracle adapter's Dataset#except now accepts a hash, giving it
  the same API as the default Dataset#except.
  
* When connecting to Microsoft SQL Server via ADO, allow
  Dataset#insert to take multiple arguments.
  
* Fractional timestamps are no longer used on ODBC.

* Schema parsing now works on MSSQL when the database is set to not
  quote identifiers.
  
* Timezone offsets are no longer used on Microsoft SQL Server, since
  they only work for the datetimeoffset type.
  
* Only 3 fractional digits in timestamps are used in Microsoft SQL
  Server, since an error is raised if the use the datetime type
  with more than that.

* The integration test suite now has guards for expected failures
  when run on known databases.  Expected failures are marked as
  pending.

Backwards Compatibility
-----------------------

* Graphing to an previously joined (but not graphed) dataset now
  causes the receiver to be wrapped in a subselect, so if you
  graph a dataset to a previously joined dataset, and then filter
  the dataset referring to tables that were in the joined dataset
  (other than the first table), the SQL produced will probably no
  longer be valid.  You should either filter the dataset before
  graphing or use the name of the first source of the joined
  dataset (which is what the subselected is aliased to) if filtering
  afterward.
  
  In certain cases, this change can cause tables to be aliased
  differently, so if you were graphing previously joined datasets
  and then filtering using the automatically generated aliases, you
  might need to modify your code.

* The DataObjects (do) adpater no longer supports DataObjects 0.9.x.

* The Dataset#virtual_row_block_call private instance method has
  been removed.

* Sequel's timezone support was significantly refactored, so if you
  had any custom modifications to the timezone support, they might
  need to be refactored as well.

* The SQL generation code was significantly refactored, so if you
  had any custom modifications in that area, you might need to
  refactor as well.
