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, Informix, JDBC, MySQL, Mysql2, ODBC, OpenBase,
Oracle, PostgreSQL, SQLite3, Swift, and TinyTDS.
Sequel 3.23.0 has been released and should be available on the gem
mirrors.
= New Features
* Sequel now allows dynamic customization for eager loading.
Previously, the parameters for eager loading were fixed at
association creation time. Now, they can be modified at query
time. To dynamically modify an eager load, you use a hash with
the proc as the value. For example, if you have this code:
Artist.eager(:albums)
And you only want to eagerly load albums where the id is greater
than or equal to some number provided by the user, you do:
min = params[:min].to_i
Artist.eager(:albums=>proc{|ds| ds.where{id > min}})
This also works when eager loading via eager_graph:
Artist.eager_graph(:albums=>proc{|ds| ds.where{id > min}})
For eager_graph, the dataset is the dataset to graph into the
current dataset, and filtering it will result in an SQL query
that joins to a subquery.
You can also use dynamic customization while cascading to also
eagerly load dependent associations, by making the hash value
a single entry hash with a proc key and the value being the
dependent associations to eagerly load. For example, if you want
to eagerly load tracks for those albums:
Artist.eager(:albums=>{proc{|ds| ds.where{id > min}}=>:tracks})
* Sequel also now allows dynamic customization for regular
association loading. Previously, this was possible by using the
association's dataset:
albums = artist.albums_dataset.filter{id > min}
However, then there was no handling of caching, callbacks, or
reciprocals. For example:
albums.each{|album| album.artist}
Would issue one query per album to get the artist, because the
reciprocal association was not set. Now you can provide a
block to the association method:
albums = artist.albums{|ds| ds.filter{id > min}}
This block is called with the dataset used to retrieve the
associated objects, and should return a modified version of that
dataset.
Note that ruby 1.8.6 doesn't allow blocks to take block arguments,
so you have to pass the block as a separate proc argument to the
association method if you are still using 1.8.6.
* Sequel now supports filtering by associations. This wasn't
previously supported as filtering is a dataset level feature and
associations are a model level feature, and datasets do not depend
on models. Now, model datasets have the ability to filter by
associations. For example, to get all albums for a given artist,
you could do:
artist = Artist[1]
Album.filter(:artist=>artist)
Since the above can also be accomplished with:
artist.albums
this may not seem like a big improvement, but it allows you to
filter on multiple associations simultaneously:
Album.filter(:artist=>artist, :publisher=>publisher)
For simple many_to_one associations, the above is just a simpler
way to do:
Album.filter(:artist_id=>artist.id, :publisher_id=>publisher.id)
Sequel supports this for all association types, including
many_to_many and many_through_many, where a subquery is used, and
it also works when composite key associations are used:
Album.filter(:artist=>artist, :tags=>tag)
This will give you the albums for that artist that are also tagged
with that tag. To provide multiple values for the same
association, mostly useful for many_to_many associations, you can
either use separate filter calls or specify the conditions as an
array:
Album.filter(:tags=>tag1).filter(:tags=>tag2)
Album.filter([[:tags, tag1], [:tags, tag2]])
* A columns_introspection extension has been added that makes
datasets attempt to guess their columns in some cases instead of
issuing a database query. This can improve performance in cases
where the columns are needed implicitly, such as graphing. After
loading the extension, you can enable the support for specific
datasets by extending them with Sequel::ColumnIntrospection. To
enable introspection for all datasets, use:
Sequel::Dataset.introspect_all_columns
* A serialization_modification_detection plugin has been added.
Previously, Sequel could not detect modifications made to
serialized objects. It could detect modification if you assigned
a new value:
model.hash_column = model.hash_column.merge(:foo=>:bar)
but not if you just modified the object directly:
model.hash_columns[:foo] = :bar
With this plugin, such modifications can be detected, at a
potentially significant performance cost.
= Other Improvements
* When using a migration directory containing both older integer
migrations and newer timestamp migrations, where some integer
migrations have not been applied, make sure to apply the remaining
integer migrations before the timestamp migrations. Previously,
they could be applied out of order due to a lexicographic sort
being used instead of a numeric sort.
* If a model does not select all columns from its table, the
insert_select optimization is no longer used. Previously,
creating a new model object for such a model could result in the
object containing columns that the model does not select.
* You can now use :select=>[] as an option for many_to_many
associations to select all columns from both the associated
table and the join table. Previously, this raised an error and
required you do :select=>'*'.lit as a workaround. The default
remains to select all columns in the associated table and none
from the join table.
* The xml_serializer plugin now handles namespaced models by
using __ instead of / as the namespace separator. Previously, /
was used and caused problems as it is not valid XML.
* The :eager_grapher association option can now accept a proc that
takes a single hash of options instead of a fixed 3 arguments.
This is the recommended way going forward of writing custom
:eager_graphers, and all of the internal ones have been converted.
The previous way of using 3 arguments is still supported.
* A bug in the identity_map plugin for many_to_one associations
without full association reflection information has been fixed.
* Sequel is now using GitHub Issues for issue tracking. Old issues
have been migrated from Google Code.
= Backwards Compatibility
* The filter by associations support breaks backward compatibilty for
users who previously added an sql_literal instance method to
Sequel::Model. Usually, that was done to for reasons similar to
but inferior than the filter by association support. The following
code can be used as a temporary workaround until you can modify
your program to use the new filter by associations support:
Sequel::Model::Associations::DatasetMethods.
send(:remove_method, :complex_expression_sql)
* The private Sequel::Model#_load_associated_objects method now takes
an additional, optional options hash. Plugins that override that
method need to be modified.
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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