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 option.

  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::DatabaseError:

  • 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,
    :dataset=>{Artist...}

  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 default.

• The eager_each plugin no longer uses Object#extend at runtime.

• Database#remove_cached_schema is now thread-safe on non-GVL ruby implementations.

• 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 needed.

• 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 removed.

• 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.