ANN: Sequel 3.44.0 Released

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)
    • Sequel::CheckConstraintViolation
    • Sequel::NotNullConstraintViolation
    • Sequel::ForeignKeyConstraintViolation
    • Sequel::UniqueConstraintViolation
    • Sequel::Postgres::ExclusionConstraintViolation
  • The :dataset association option can now take accept an optional
    association reflection option. Instead of doing:

    Album.one_to_many :artists,

    you can now do:

    Album.one_to_many :artists,
    :dataset=>{|r| r.associated_dataset…}

    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.

    DB[:table].order(:column1).limit(10, 10).
    from_self.order(:column2).limit(5, 5)

    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
    from tables.

  • 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
    helpful messages.

  • 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
    non-literal string.

  • 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
    been removed.

  • :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.


  • Sequel::ForeignKeyConstraintViolation
  • Sequel::UniqueConstraintViolation
  • Sequel::Postgres::ExclusionConstraintViolation

That is … just pure awesomeness. Thanks a lot for that!!!