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, CUBRID,
DataObjects, DB2, DBI, Firebird, IBM_DB, Informix, JDBC, MySQL,
Mysql2, ODBC, OpenBase, Oracle, PostgreSQL, SQLite3, Swift, and
Sequel 3.44.0 has been released and should be available on the gem
= New Features
Dataset#paged_each has been added, for processing entire datasets
without keeping all rows in memory, even if the underlying driver
keeps all query results in memory. This is implemented using
limits and offsets, and requires an order (model datasets use a
default order by primary key). It defaults to fetching 1000
rows at a time, but that can be changed via the :rows_per_fetch
This method is drop-in compatible for each. Previously, the
pagination extension’s each_page method could be used for a
similar purpose, but users of each_page are now encouraged to
switch to paged_each.
Sequel now recognizes constraint violation exceptions on most
databases, and will raise specific exceptions for different
types of constraint violations, instead of the generic
- Sequel::ConstraintViolation (generic superclass)
The :dataset association option can now take accept an optional
association reflection option. Instead of doing:
you can now do:
This second form will preform better.
Temporary views are now supported on PostgreSQL and SQLite using
the :temp option to create_view.
= Other Improvements
Row fetching speed in the tinytds adapter has been increased by
up to 60%.
Row fetching speed in the mysql2 adapter when using an identifier
output method has been increased by up to 50%.
On databases where offsets are emulated via the ROW_NUMBER window
function (Oracle, DB2, Microsoft SQL Server), using an offset in
a subselect is now supported. For example, the following code
previously didn’t work correctly with emulated offsets:
Second 5 rows ordered by column2 of the second 10 rows ordered
by column 1.
Row processing speed has been increased slightly for all adapters
that supported databases where offsets are emulated.
Association method performance has improved by caching an
intermediate dataset. This can close to triple the performance
of the association_dataset method, and increase the performance
of the association method by close to 30%.
Virtual Row performance has increased about 30% in the typical
case by using a shared VirtualRow instance.
Database#create_or_replace_view is now emulated on databases that
don’t support it directly by dropping the view before attempting
to create it.
The columns_introspection extension can now introspect for simple
select * queries from subselects, and it can now use the cached
schema information in the database for simple select * queries
The identity_map plugin now works correctly with many-to-many
right-side composite keys.
Dataset#last for Model datasets now works even if you don’t specify
an order explicitly, giving the last entry by primary key. Note
that Dataset#first for model datasets still does not order by
The eager_each plugin no longer uses Object#extend at runtime.
Database#remove_cached_schema is now thread-safe on non-GVL ruby
Connection errors in the jdbc adapter now provide slightly more
Sequel now uses the standard offset emulation code in the
jdbc/as400 adapter, instead of custom offset emulation code
specific to that adapter.
Database#create_view with a dataset now works correctly when using
the pg_auto_parameterize extension.
Database#columns no longer calls the row_proc.
Dataset#schema_and_table no longer turns a literal string into a
The oracle adapter now works with a :prefetch_rows=>nil option,
which explicitly disables prefetching.
The mock mssql adapter now sets a server_version so that more
parts of it work.
= Backwards Compatibility
Offset emulation via ROW_NUMBER works by moving the query to a
subselect that also selects from the ROW_NUMBER window function,
and filtering on the ROW_NUMBER in the main query. Previously, the
ROW_NUMBER was also present in the output columns, and some
adapter code was needed to hide that fact. Now, the outer select
selects all of the inner columns in the subselect except for the
ROW_NUMBER, reducing the adapter code needed. This has the side
effect of potentially requiring a query (or multiple queries for
multiple subselects) to determine the columns to use. The
columns_introspection extension may reduce the number of queries
The correlated_subquery eager limit strategy is no longer supported
on Microsoft SQL Server for many_*_many associations. As the
window_function eager limit strategy is supported there, there is
no reason to use the correlated_subquery strategy.
The public AssociationReflection#_dataset_method method has been
The private _*_dataset methods for associations (e.g.
_albums_dataset) have been removed.
The private Dataset#offset_returns_row_number_column? method has
:conditions options for associations are now added to the
association dataset before the foreign key filters, instead of
after. This should have no effect unless you were introspecting
the dataset’s opts or sql and acting on it.
The added abilities in the columns_introspection plugin to use
cached schema for introspection can now cause it to return
incorrect results if the table’s schema has changed since it was
cached by Sequel.