rails/activerecord/CHANGELOG.md

*   Introduce `force: :cascade` option for `create_table`. Using this option
    will recreate tables even if they have dependent objects (like foreign keys).
    `db/schema.rb` now uses `force: :cascade`. This makes it possible to
    reload the schema when foreign keys are in place.

    *Matthew Draper*, *Yves Senn*

*   `db:schema:load` and `db:structure:load` no longer purge the database
    before loading the schema. This is left for the user to do.
    `db:test:prepare` will still purge the database.

    Closes #17945.

    *Yves Senn*

*   Fix undesirable RangeError by Type::Integer. Add Type::UnsignedInteger.

    *Ryuta Kamizono*

*   Add `foreign_type` option to `has_one` and `has_many` association macros.

    This option enables to define the column name of associated object's type for polymorphic associations.

    *Ulisses Almeida, Kassio Borges*

*   Remove deprecated behavior allowing nested arrays to be passed as query
    values.

    *Melanie Gilman*

*   Deprecate passing a class as a value in a query. Users should pass strings
    instead.

    *Melanie Gilman*

*   `add_timestamps` and `remove_timestamps` now properly reversible with
    options.

    *Noam Gagliardi-Rabinovich*

*   `ActiveRecord::ConnectionAdapters::ColumnDumper#column_spec` and
    `ActiveRecord::ConnectionAdapters::ColumnDumper#prepare_column_options` no
    longer have a `types` argument. They should access
    `connection#native_database_types` directly.

    *Yves Senn*

Please check [4-2-stable](https://github.com/rails/rails/blob/4-2-stable/activerecord/CHANGELOG.md) for previous changes.