Sequel is a lightweight database access toolkit for Ruby.
* Sequel provides thread safety, connection pooling and a concise
DSL for constructing SQL queries and table schemas.
* Sequel includes a 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, savepoints,
two-phase commit, transaction isolation, master/slave
configurations, and database sharding.
* Sequel currently has adapters for ADO, Amalgalite, DataObjects,
DB2, DBI, Firebird, IBM_DB, Informix, JDBC, MySQL, Mysql2, ODBC,
OpenBase, Oracle, PostgreSQL, SQLite3, Swift, and TinyTDS.
Sequel 3.28.0 has been released and should be available on the gem
mirrors.
= New Adapter Support
* Sequel now has much better support for the DB2 database.
* An ibmdb adapter has been added, and is the recommended adapter to
to use if you want to connect to DB2 from MRI.
* A jdbc db2 subadapter has been added, allowing good DB2 support on
JRuby.
* The db2 adapter has been cleaned up substantially, and now works
well, but it is still recommended that you switch to ibmdb if you
are using the db2 adapter.
* The firebird adapter has been split into shared and specific parts,
and quite a few fixes were made to it.
* A jdbc firebird subadapter has been added, allowing connection to
firebird databases from JRuby.
= New PostgreSQL 9.1 Features
* Dataset#returning has been added for using the RETURNING clause on
INSERT/UPDATE/DELETE queries. RETURNING allows such queries to
return results in much the same way as a SELECT query works.
When Dataset#returning is used, Dataset #insert, #update, and
#delete now accept a block that is passed to Dataset #fetch_rows
which is yielded plain ruby hashes for each row inserted, updated,
or deleted. If Dataset#returning is used and a block is not given
to those methods, those methods will return an array of plain hashes
for all rows inserted, updated, and deleted.
* Dataset#with_sql now treats a symbol as a first argument as a method
name to call to get the SQL. The expected use case for this is with
Dataset#returning and insert/update/delete:
DB[:items].
returning(:id).
with_sql(:update_sql, :b => :b + 1).
map(:id)
Basically, it makes it more easily to statically set the
insert/update/delete SQL, and then be able to use the full
dataset API for returning results. As mentioned above, using
Dataset#returning with #insert, #update, and #delete yields plain
hashes, so if you want to have the row_proc applied (e.g. you are
using models), you need to use this method instead, since you can
then call #each or #all to make sure the row_proc is called on all
returned rows.
* Dataset#with (common table expressions) now affects
INSERT/UPDATE/DELETE queries.
* Database#create_table? now uses CREATE TABLE IF NOT EXISTS on
PostgreSQL 9.1.
= Other New Features
* The :limit option is now respected when eager loading via either
eager or eager_graph. By default, Sequel will just do an array
slice of the resulting ruby array, which gets the correct answer,
but does not offer any performance improvements. Sequel also
offers a new :eager_limit_strategy option for using more advanced
query types that only load the related records from the database.
The available values for the :eager_limit_strategy option are:
:window_function: This uses the row_number window function
partitioned by the related key fields. It can only be used
on databases that support window functions (PostgreSQL 8.4+,
Microsoft SQL Server 2005+, DB2).
:correlated_subquery: This uses a correlated subquery that is
limited. It works on most databases except MySQL and DB2.
You can provide a value of true as the option to have Sequel
pick a strategy to use. Sequel will never use a correlated
subquery for true, since in some cases it can perform worse than
loading all related records and doing the array slice in ruby.
If you want to enable an eager_limit_strategy globally, you can
set Sequel::Model.default_eager_limit_strategy to a value, and
all associations that use :limit will default to using that
strategy.
* one_to_one associations that do not represent true one-to-one
database relationships, but represent one-to-many relationships
where you are only returning the first object based on a given
order are also now handled correctly when eager loading.
Previously, eager loading such associations resulted in the last
matching object being associated instead of the first matching
object being associated.
You can also use an :eager_limit_strategy for one_to_one
associations. In addition to the :window_function and
:correlated_subquery values, there is also a :distinct_on value
that is available on PostgreSQL for using DISTINCT ON, which is
the fastest strategy if you are using PostgreSQL.
* Dataset#map, #to_hash, #select_map, #select_order_map, and
#select_hash now accept arrays of symbols, and if given arrays
of symbols, use arrays of results. For example:
DB[:items].map([:id, :name])
# => [[1, 'foo'], [2, 'bar'], ...]
DB[:items].to_hash([:id, :foo_id], [:name, :bar_id])
# => {[1, 3]=>['foo', 5], [2, 4]=>['bar', 6], ...}
* For SQL expression objects where Sequel cannot deduce the type
of the object, it now will consider the type of the argument
when a &, |, or + operator is used. For example:
:x & 1
Previously, this did "x AND 1", now it does "x & 1". Using a
logical operator on an integer doesn't make sense, but it's
possible people did so if the database uses 1/0 for true/false.
Likewise:
:x + 'foo'
Previously, this did "x + 'foo'" (addition), now it does
"x || 'foo'" (string concatenation).
* The sql_string, sql_number, and sql_boolean methods are now
available on SQL::ComplexExpressions, so you can do:
(:x + 1).sql_string + ' foos'
# (x + 1) || ' foos'
Previously, there was not an easy way to generate such SQL
expressions.
* :after_load association hooks are now applied when using
eager_graph. Previously, they were only applied when using
eager, not when using eager_graph.
* Database#copy_table has been added to the postgres adapter if pg
is used as the underlying driver. It allows you to get very
fast exports of table data in text or CSV format. It also
accepts datasets, allowing fast exports of arbitrary queries
in text or CSV format.
* SQL extract support (:timestamp.extract(:year)) is now emulated
on the databases that don't natively support it, such as SQLite,
Microsoft SQL Server, and DB2. At least the following values are
supported for extraction: :year, :month, :day, :hour, :minute,
and :second.
* The bitwise XOR operator is now emulated on SQLite. Previously,
attempting to use it would cause the database to raise an error.
* A Database#use_timestamp_timezones accessor has been added on
SQLite. This allows you to turn off the use of timezones in
timestamps by setting the value to false. This is necessary if you
want you want to use the SQLite datetime functions, or the new
ability to emulate extract.
Note that this setting does not affect the current database
content. To convert old databases to the new format, you'll
have to resave all rows that have timestamps.
At some point in the future, Sequel may default to not using
timezones in timestamps by default on SQLite, so if you would
like to rely on the current behavior, you should set this
accessor to true now.
* Sequel now works around bugs in MySQL when using a subselect with
a LIMIT by using a nested subselect.
* Sequel now works around issues in Microsoft SQL Server and DB2 when
using a subselect with IN/NOT IN that uses the emulated offset
support.
* The jdbc adapter now returns java.sql.Clob objects as
Sequel::SQL::Blobs.
* Sequel now considers database clob types as the :blob schema type.
* Sequel::SQLTime.create has been added for more easily creating
instances:
Sequel::SQLTime.create(hour, minute, second, usec)
* Dataset#select_all now accepts SQL::AliasedExpression and
SQL::JoinClause arguments and returns the appropriate
SQL::ColumnAll value that selects all columns from the related
table.
* Model.set_dataset now accepts Sequel::LiteralString objects that
represent table names. This usage is not encouraged except in
rare cases such as using a set returning function in PostgreSQL.
* Dataset#supports_cte? now takes an optional argument specifying the
type of query (:insert, :update, :delete, :select). It defaults to
:select.
* Dataset#supports_returning? has been added. It requires an
argument specifying the type of query (:insert, :update, or
:delete).
* Dataset#supports_cte_in_subqueries? has been added for checking
for support for this ability. Apparently, only PostgreSQL
currently supports this. For other adapters that support CTEs but
not in subqueries, if a subquery with a CTE is used in a JOIN, the
CTE is moved from the subquery to the main query.
* Dataset#supports_select_all_and_column has been added for seeing
if "SELECT *, foo ..." style queries are supported. This is false
on DB2, which doesn't allow such queries. When it is false, using
select_append on a dataset that doesn't specifically select columns
will now change the query to do "SELECT table.*, foo ..." instead,
working around the limitation on DB2.
* Dataset#supports_ordered_distinct_on? has been added. Currently,
this is only true on PostgreSQL. MySQL can emulate DISTINCT ON
using GROUP BY, but it doesn't respect ORDER BY, so it some
cases it cannot be used equivalently.
* Dataset#supports_where_true? has been added for checking for support
of WHERE TRUE (or WHERE 1 if 1 is true). Not all databases support
using such a construct, and on the databases that do not, you have
to use WHERE (1 = 1) or something similar.
= Other Improvements
* Sequel 3.27.0 was negatively affected by a serious bug in
ActiveSupport's Time.=== that has still not been fixed, which
broke the literalization of Time objects. In spite of the bad
precedent it sets, Sequel now avoids using Time.=== on a
subclass of Time to work around this ActiveSupport bug.
* Dataset#with_pk now uses a qualified primary key instead of an
unqualified primary key, which means it can now be used correctly
after joining to a separate table.
* Association after_load hooks when lazy loading are now called
after the association has been loaded, which allows them to change
which records are cached. This makes the lazy load case more
similar to the eager load case.
* The metaprogrammatically created methods that implement Sequel's
DSL support have been made significantly faster by using
module_eval instead of define_method.
* The type translation in the postgres, mysql, and sqlite adapters
has been made faster by using Method objects that result in more
direct processing.
* Typecasting values for time columns from Time values to
Sequel::SQLTime values now correctly handles fractional seconds on
ruby 1.9.
= Backwards Compatibility
* Dataset#insert_returning_sql has been changed to a private method
in the PostgreSQL and Firebird adapters, and it operates
differently than it did previously. The private
#insert_returning_pk_sql and #insert_returning_select_sql methods
have been removed.
* Dataset#with_pk no longer does some defensive checking for misuse of
primary keys (e.g. providing a composite key when the model uses
a single key). Previously, Sequel would raise an Error
immediately, now such behavior is undefined, with the most likely
behavior being the database raising an Error.
* The :alias_association_type_map and :alias_association_name_map
settings have been removed from the :eager_graph dataset option,
in favor of just storing the related association reflection.
* The internals of the db2 adapter have changed substantially, if you
were relying on some of the private methods defined in it, you will
probably have to modify your code.
* The firebird adapter was substanially modified, specifically parts
related to insert returning autogenerated primary key values, so if
you were previously using the adapter you should probably take more
care than usual when testing your upgrade.
* The Dataset::WITH_SUPPORTED constant has been removed.
* The Dataset#supports_cte? method now accepts an optional argument.
If you overrode this method, your overridden method now must
accept an optional argument.
* If you were previously doing:
:x & 1
and wanting "x AND 1", you have to switch to:
:x.sql_boolean & 1
Likewise, if you were previously doing:
:x + 'foo'
and wanting "x + 'foo'", you need to switch to:
:x.sql_number + 'foo'
* Sequel no longer does defensive type checking in the SQL expression
support, as it was often more strict than the database and would
not allow the creation of expressions that were valid for the
database.
Thanks,
Jeremy
* {Website}[http://sequel.rubyforge.org]
* {Source code}[http://github.com/jeremyevans/sequel]
* {Blog}[http://sequel.heroku.com]
* {Bug tracking}[http://github.com/jeremyevans/sequel/issues]
* {Google group}[http://groups.google.com/group/sequel-talk]
* {RDoc}[http://sequel.rubyforge.org/rdoc]
···
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