ANN: Sequel 3.28.0 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, DataObjects,
    DB2, DBI, Firebird, IBM_DB, Informix, JDBC, MySQL, Mysql2, ODBC,
    OpenBase, Oracle, PostgreSQL, SQLite3, Swift, and TinyTDS.

Sequel 3.28.0 has been released and should be available on the gem
mirrors.

= 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.

Thanks,
Jeremy

On Tue, Oct 4, 2011 at 1:05 AM, Jeremy E. [email protected]
wrote:

Sequel is a lightweight database access toolkit for Ruby.

is it possible to replace arel and use sequel instead as engine for
activerecord?
just asking.
kind regards -botp

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