Sequel is a lightweight database access toolkit for Ruby.

* Sequel provides thread safety, connection pooling and a concise DSL
  for constructing database queries and table schemas.
* Sequel also includes a lightweight but comprehensive ORM layer for
  mapping records to Ruby objects and handling associated records.
* Sequel supports advanced database features such as prepared
  statements, bound variables, stored procedures, master/slave
  configurations, and database sharding.
* Sequel makes it easy to deal with multiple records without having
  to break your teeth on SQL.
* Sequel currently has adapters for ADO, Amalgalite, DataObjects,
  DB2, DBI, Firebird, Informix, JDBC, MySQL, ODBC, OpenBase, Oracle,
  PostgreSQL and SQLite3.

Sequel 3.8.0 has been released and should be available on the gem
mirrors.

New Features
------------

* Dataset#each_server was added, allowing you to run the same query
  (most likely insert/update/delete) on all shards.  This is useful
  if you have a sharded database but have lookup tables that should
  be identical on all shards.  It works by yielding copies of the
  current dataset that are tied to each server/shard:

    DB[:table].filter(:id=>1).each_server do |ds|
      ds.update(:name=>'foo')
    end

* Database#each_server was added, allowing you to run schema
  modification methods on all shards.  It works by yielding a
  new Sequel::Database object for each shard, that will connect to
  only that shard:

    DB.each_server do |db|
      db.create_table(:t){Integer :num}
    end

* You can now add and remove servers/shards from the connection
  pool while Sequel is running:

    DB.add_servers(:shard1=>{:host=>'s1'}, :shard2=>{:host=>'s2'})
    DB.remove_servers(:shard1, :shard2)

* When you attempt to disconnect from a server that has connections
  currently in use, Sequel will now schedule those connections to
  be disconnected when they are returned to the pool.  Previously,
  Sequel disconnected available connections, but ignored connections
  currently in use, so it wasn't possible to guarantee complete
  disconnection from the server.  Even with this new feature, you can
  only guarantee eventual disconnection, since disconnection of
  connections in use happens asynchronously.

* Database#disconnect now accepts a :servers option specifying the
  server(s) from which to disconnect.  This should be a symbol or
  array of symbols representing servers/shards.  Only those specified
  will be disconnected:

    DB.disconnect(:servers=>[:shard1, :shard2])

* A validates_type validation was added to the validation_helpers
  plugin.  It allows you to check that a given column contains
  the correct type.  I can be helpful if you are also using the
  serialization plugin to store serialized ruby objects, by making
  sure that the objects are of the correct type (e.g. Hash):

    def validate
      validates_type(Hash, :options)
    end

* Sequel::SQL::Expression#== is now supported for all expressions:

    :column.qualify(:table).cast(:type) == \
      :column.qualify(:table).cast(:type)
    # => true
    :column.qualify(:table).cast(:type) == \
      :other_column.qualify(:table).cast(:type)
    # => false

* When using the generic File type to create blob columns on
  MySQL, you can specify the specific database type by using the
  :size option (with :tiny, :medium, and :long values recognized):

    DB.create_table(:docs){File :body, :size=>:long} # longblob

* The mysql adapter will now default to using mysqlplus, falling
  back to use mysql.  mysqlplus is significantly better for threaded
  code because queries do not block the entire interpreter.

* The JDBC adapter is now able to detect certain types of disconnect
  errors.

* ConnectionPool.servers and Database.servers were added, which
  return an array of symbols specifying the servers/shards in use.

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

* The single-threaded connection pool now raises
  DatabaseConnectionErrors if unable to connect, so it now operates
  more similarly to the default connection pool.

* The single-threaded connection pool now operates more similar
  to the default connection pool when given a nonexistent server.

* PGErrors are now correctly converted to DatabaseErrors in the
  postgres adapter when preparing statements or executing prepared
  statements.

* DatabaseDisconnectErrors are now raised correctly in the postgres
  adapter if the connection status is not OK after a query raises an
  error.

* In the mysql adapter, multiple statements in a single query should
  now be handled correctly in the all cases, not just when using
  Dataset#each.  So you can now submit multiple queries in a single
  string to Database#run.

* Model object creation on Microsoft SQL Server 2000 once again
  works correctly.  Previously, an optimization was used that was
  only supported on 2005+.

* Backslashes are no longer doubled inside string literals when
  connecting to Microsoft SQL Server.

* The ORDER clause now correctly comes after the HAVING clause on
  Microsoft SQL Server.

* Sequel now checks that there is an active transaction before
  rolling back transactions on Microsoft SQL Server, since
  there are cases where Microsoft SQL Server will roll back
  transactions implicitly.

* Blobs are now handled correctly when connecting to H2.

* 64-bit integers are now handled correctly in JDBC prepared
  statements.

* In the boolean_readers plugin, correctly handle columns not in
  the db_schema, and don't raise an error if the model's columns
  can't be determined.

* In the identity_map plugin, remove instances from the cache if they
  are deleted or destroyed.

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

* Dataset::FROM_SELF_KEEP_OPTS was merged into
  Dataset::NON_SQL_OPTIONS.  While used in different places, they
  were used for the same purpose, and entries missing from one should
  have been included in the other.

* The connection pool internals changed substantially.  Now,
  ConnectionPool #allocated and #available_connections will return
  nil instead of an array or hash if they are called with a
  nonexistent server.  These are generally only used internally,
  though they are part of the public API.  #created_count and #size
  still return the size of the :default server when called with a
  nonexistent server, though.

* The meta_eval and metaclass private methods were removed from
  Sequel::MetaProgramming (only the meta_def public method remains).
  If you want these methods, use the metaid gem.

* The irregular ox->oxen pluralization rule was removed from the
  default inflections, as it screws up the more common box->boxes.

Thanks,
Jeremy

* {Website}[http://sequel.rubyforge.org]
* {Source code}[http://github.com/jeremyevans/sequel]
* {Bug tracking}[http://code.google.com/p/ruby-sequel/issues/list]
* {Google group}[http://groups.google.com/group/sequel-talk]
* {RDoc}[http://sequel.rubyforge.org/rdoc]
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