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, DataObjects, DB2, DBI,
  Firebird, Informix, JDBC, MySQL, ODBC, OpenBase, Oracle, PostgreSQL
  and SQLite3.

Sequel 2.10.0 has been released and should be available on the gem
mirrors.  The 2.10.0 release adds numerous improvements:

New Supported Adapters and Databases
------------------------------------

* A DataObjects adapter was added that supports PostgreSQL,
  MySQL, and SQLite.  DataObjects is the underlying database
  library used by DataMapper, and has potential performance
  advantages by doing all typecasting in C.

* A Firebird Adapter was added, it requires the modified Ruby
  Fb adapter found at http://github.com/wishdev/fb.

* An H2 JDBC subadapter was added, based on the code used in JotBot.
  H2 is an embeddable Java database, and may be preferable to using
  SQLite on JDBC because SQLite requires native code.

New Core Features
-----------------

* Sequel now has database independent migrations.  Before, column
  types in migrations were not translated per database, so it was
  difficult to set up a migration that worked on multiple databases.
  Sequel now accepts ruby classes as database types, in addition to
  symbols and strings.  If a ruby class is used, it is translated
  to the most appropriate database type.  Here is an example using
  all supported classes (with Sequel's default database type):

    DB.create_table(:cats) do
      primary_key :id, :type=>Integer # integer
      String :a                       # varchar(255)
      column :b, File                 # blob
      Fixnum :c                       # integer
      foreign_key :d, :other_table, :type=>Bignum # bigint
      Float :e                        # double precision
      BigDecimal :f                   # numeric
      Date :g                         # date
      DateTime :h                     # timestamp
      Time :i                         # timestamp
      Numeric :j                      # numeric
      TrueClass :k                    # boolean
      FalseClass :l                   # boolean
    end

  Type translations were tested on the PostgreSQL, MySQL, SQLite,
  and H2 databases.  The default translations should work OK for
  most databases, but there will probably be a type or two that
  doesn't work.  Please send in a patch if Sequel uses a column type
  that doesn't work on your database.

  Note that existing migrations still work fine, in most cases.  If
  you were using strings or symbols for types before, they should
  still work.  See the Backwards Compatibility section below for
  details.

  Also note that this doesn't relate solely to migrations, as any
  database schema modification method that accepts types will
  accept one of the above classes.

* A ton of internal work was done to better support databases that
  fold unqouted identifiers to uppercase (which is the SQL standard).
  Sequel now allows you to set a method to call on identifiers going
  both into and out of the database.  The default is to downcase
  identifiers coming out, and upcase identifiers going in, though
  this is overridden by the PostgreSQL, MySQL, and SQLite adapters
  to not do anything (since they fold to lowercase by default).

  The settings are called identifier_input_method and
  identifier_output_method, and like most Sequel settings, they can
  be set globally, per database, or per dataset:

    # Global (use uppercase in ruby and lowercase in the database)
    Sequel.identifier_input_method = :downcase
    Sequel.identifier_output_method = :upcase
    # Per Database (use camelized names in the database, and
    #               underscored names in ruby)
    DB.identifier_input_method = :camelize
    DB.identifier_output_method = :underscore
    # Per Dataset (obfuscate your database columns!)
    class String; def rot_13; tr('A-Za-z', 'N-ZA-Mn-za-m') end end
    ds = DB[:table]
    ds.identifier_input_method = :rot_13
    ds.identifier_output_method = :rot_13

* Schema parsing support was added to the JDBC adapter, using the
  JDBC metadata methods.  This means that models that use the
  JDBC adapter will typecast data in their column setters and
  automatically select the correct primary key column(s).  This is
  currently the only adapter that supports schema parsing when using
  an MSSQL or Oracle database.

* Database#create_table now takes options, which you can use to
  specify a MySQL engine, charset, and/or collation.  You can also
  set a default engine, charset, and collation for MySQL to use:

    Sequel::MySQL.default_engine = 'InnoDB'
    Sequel::MySQL.default_charset = 'utf8'
    Sequel::MySQL.default_collate = 'utf8'

  The defaults will be used if the options are not provided.  If a
  default engine is set, you can specify :engine=>nil to not use it
  (same goes for charset and collate).

* The Sequel::DatabaseConnectionError exception class was added.  It
  is raised by the connection pool if there is an error attempting
  to instantiate a database connection.  Also, if the adapter returns
  nil instead of raising an error for faulty connection parameters,
  DatabaseConnectionError will be raised immediately, instead of the
  connection pool busy waiting until if gives up with a
  PoolTimeoutError.

* Database#tables is now supported on the JDBC adapter, returning
  an Array of table name symbols.

* Sequel now converts the following Java types returned by the JDBC
  adapter into ruby types: Java::JavaSQL::Timestamp,
  Java::JavaSQL::Time, Java::JavaSQL::Date,
  Java::JavaMath::BigDecimal, and Java::JavaIo::BufferedReader.

* When using the PostgreSQL adapter with the postgres-pr driver,
  Sequel will use a custom string escaping routine unless
  force_standard_strings = false.  This means that using Sequel's
  defaults, postgres-pr will correctly escape strings now.

* The SQLite adapter now returns float, real, and double precision
  columns as Floats.

* The SQLite adapter logs beginning, committing, and rolling back
  transactions.

* Sequel now has an internal version (before, the only way to tell
  the version was to look at the gem being used).  It is accessible
  at Sequel.version.

New Model Features
------------------

* A new validates_not_string validation was added for Sequel Models.
  It is intended to be used with the raise_on_typecast_failure =
  false setting.  In this case, for a non-string database column,
  if there is a string value when the record is going to be
  saved, it is due to the fact that Sequel was not able to typecast
  the given data correctly (so it is almost certainly not valid).
  This should make Sequel easier to use with web applications.

* An :allow_missing validation option was added to all standard
  validations.  This option skips the validation if the attribute
  is not in the object's values.  It is different from :allow_nil,
  which will skip the value if it is present but nil in the values.
  The intended use case for this option is when the database provides
  a good default.  If the attribute is not present in values, the
  database will use its default.  If the attribute is present in
  the values but equals nil, Sequel will attempt to insert it into
  the database as a NULL value, instead of using the database's
  default.  If you don't want Sequel to insert a NULL value in the
  database, but you want the database to provide the default, this
  is the option to use.

* validates_each now accepts :allow_nil and :allow_blank options,
  so it is easier to create custom validations with the same options
  as the standard validations.

* Before_* hooks now run in the reverse order that they were added.
  The purpose of hooks is to wrap existing functionality, and making
  later before_* hooks run before previous before_* hooks is the
  correct behavior.

* You can now add you own hook types, via Model.add_hook_type.  This
  is intended for plugin use.  All of the standard hooks are now
  implemented using this method.

* The value of new? in a after_save hook now reflects the
  previous state of the model (so true for a create and false for an
  update), instead of always being false.  This makes it easier
  to have a complex after_save hook that still needs to
  differentiate between a newly created record and an updated record,
  without having to add separate after_create and after_update
  hooks.

* The value of changed_columns in an after_update hook now reflects
  the value before the update occurred, instead of usually being
  empty.  Previously, to have this functionality, you generally had
  to save the value to an instance variable in a before_update hook
  so you could reference it in the after_update hook.

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

* Sequel now longer overwrites the following Symbol instance methods
  when running on ruby 1.9: [], <, <=, >, and >=.  One of Sequel's
  principals is that it does not override methods defined by ruby,
  and now that ruby 1.9 defines the above methods on Symbol, Sequel
  shouldn't be overwriting them.

  Sequel already provides a way to work around this issue when
  another library adds the same methods to Symbol that Sequel does.
  For example, you need to change the following:

    dataset.filter(:number > 1)
    dataset.filter(:number >= 2)
    dataset.filter(:name < 'M')
    dataset.filter(:name <= 'I')
    dataset.filter(:is_bool[:x])

  To:

    dataset.filter{|o| o.number > 1}
    dataset.filter{|o| o.number >= 2}
    dataset.filter{|o| o.name < 'M'}
    dataset.filter{|o| o.name <= 'I'}
    dataset.filter{|o| o.is_bool(:x)}

  The argument provided to the block is a Sequel::SQL::VirtualRow.
  This class uses method_missing so that any methods called on it
  return Sequel::SQL::Identifiers (if no arguments are provided)
  or Sequel::SQL::Function (if arguments are provided).

  If you were using one of the above symbol methods outside of a
  filter, you can to call sql_string, sql_number, or sql_function
  on the symbol.  So the following would also work:

    dataset.filter(:number.sql_number > 1)
    dataset.filter(:number.sql_number >= 2)
    dataset.filter(:name.sql_string < 'M')
    dataset.filter(:name.sql_number <= 'I')
    dataset.filter(:is_bool.sql_function(:x))

  Using the block argument makes for a nicer API, though, so I
  recommend using it when possible.

  Note that if you are running ruby 1.8 or jruby without the --1.9
  flag, you don't need to worry.  If you are running ruby 1.9 or
  jruby --1.9, or you plan to at some point in the future, you
  should inspect your code for existing uses of these methods.
  Here are a couple command lines that should find most uses:

    # Find :symbol[]
    egrep -nr ':['\''"]?[a-zA-Z_0-9]*['\''"]?\[' *
    # Find :symbol (<|>|<=|>=)
    egrep -nr '[^:]:['\''"]?[a-zA-Z_0-9]*['\''"]? *[<>]=?' *

* Database#quote_identifiers now affects future schema modifications
  when using the database.  Previous, it only affected future
  schema modifications if a schema modification method had not yet
  been called.

* Literalization of Times and DateTimes is now correct when using the
  MySQL JDBC subadapter.

* Literalization of Blobs is now correct when using the PostgreSQL
  JDBC subadapter.

* Index and table names are quoted when creating indices in the
  PostgreSQL adapter.

* Dataset#delete was changed in the SQLite adapter to add a
  where clause that is always true, instead of doing an explicit
  count first and the deleting.  This is simpler, though it
  could potentially have performance implications.

* The sequel command line tool now supports symbol keys and unnested
  hashes in YAML files, so it should work with Merb's database.yml.
  It also includes the error class in the case of an error.

* The integration type tests were greatly expanded.  Generally,
  running the integration tests is a good way to determine how well
  your database is supported.

* Dataset#quote_identifier now returns LiteralStrings as-is, instead
  of treating them as regular strings.

* Sequel no longer modifies the MySQL::Result class when using the
  MySQL adapter.

Backwards Compatibilty
----------------------

* If you were previously using a database that returned uppercase
  identifiers, it will probably return lowercase identifiers by
  default now.  To get back the old behavior:

    DB.identifier_output_method = nil

* The module hierarchy under Sequel::SQL has changed.  Now,
  modules do not include other modules, and the following modules
  were removed since they would have been empty after removing
  the modules they included: Sequel::SQL::SpecificExpressionMethods
  and Sequel::SQL::GenericExpressionMethods.

* Sequel no longer assumes the public schema by default when
  connecting to PostgreSQL.  You can still set the default
  schema to use (even to public).

* The ability to load schema information for all tables at once
  was removed from the PostgreSQL adapter.  While it worked, it had
  some issues, and it was difficult to keep it working when some
  new features were used.  This ability wasn't exposed to the user,
  and was purely an optimization.  If you have any code like:

    DB.schema

  by itself after the Database object was instantiated, you should
  remove it.

* The Database#primary_key API changed in the PostgreSQL shared
  adapter, it now accepts an options hash with :server and :conn keys
  instead of a server symbol.  Also, quite a few private Database
  instance methods changed, as well as some constants in the
  AdapterMethods.

* It is possible that some migrations will break, though it is
  unlikely.  If you were using any of the classes mentioned above
  as a method inside a migration, it might be broken.  However,
  since String, Float, and Integer wouldn't have worked as methods
  before, it is unlikely that anyone used this.

* The meaning of #String, #Integer, and #Float inside
  Sequel::SQL::Generator (i.e. inside a Database#create_table
  block) has changed.  Before, these used to call private Kernel
  methods, now, they set up columns with the appropriate database
  type.

* The Database#lowercase method in the DBI adapter was removed,
  as its use case is now met by the identifier_output_method support.

* Database#uri is now aliased explicitly via a real method, to
  allow for easier subclassing.

* You can no longer pass nil as the second argument to
  Database#create_table.

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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