# 3.28.0.txt

Path: | doc/release_notes/3.28.0.txt
Last Update: | Sun May 19 07:59:58 +0000 2013

# 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.

[Validate]