This reverts commit 761bc751.

This commit wasn't fixing any issue just using the same table for
different models with different primary keys.

If your database supports setting the isolation level for a transaction,
you can set it like so:

  Post.transaction(isolation: :serializable) do
    # ...
  end

Valid isolation levels are:

* `:read_uncommitted`
* `:read_committed`
* `:repeatable_read`
* `:serializable`

You should consult the documentation for your database to understand the
semantics of these different levels:

* http://www.postgresql.org/docs/9.1/static/transaction-iso.html
* https://dev.mysql.com/doc/refman/5.0/en/set-transaction.html

An `ActiveRecord::TransactionIsolationError` will be raised if:

* The adapter does not support setting the isolation level
* You are joining an existing open transaction
* You are creating a nested (savepoint) transaction

The mysql, mysql2 and postgresql adapters support setting the
transaction isolation level. However, support is disabled for mysql
versions below 5, because they are affected by a bug
(http://bugs.mysql.com/bug.php?id=39170) which means the isolation level
gets persisted outside the transaction.

Closes #6960

If assigning to a has_many :through collection against an unsaved
object using the collection=[<array_of_items>] syntax, the join models
were not properly created, previously.

Having column related schema dumper code in the AbstractAdapter. The
code remains the same, but by placing it in the AbstractAdapter, we can
then overwrite it with Adapter specific methods that will help with
Adapter specific data types.

The goal of moving this code here is to create a new migration key for
PostgreSQL's array type. Since any datatype can be an array, the goal is
to have ':array => true' as a migration option, turning the datatype
into an array. I've implemented this in postgres_ext, the syntax is
shown here: https://github.com/dockyard/postgres_ext#arrays

Adds array migration support

Adds array_test.rb outlining the test cases for array data type
Adds pg_array_parser to Gemfile for testing
Adds pg_array_parser to postgresql_adapter (unused in this commit)

Adds schema dump support for arrays

Adds postgres array type casting support

Updates changelog, adds note for inet and cidr support, which I forgot to add before

Removing debugger, Adds pg_array_parser to JRuby platform

Removes pg_array_parser requirement, creates ArrayParser module used by
PostgreSQLAdapter

Allows you to specify the model association key in a belongs_to
relationship instead of the foreign key.

The following queries are now equivalent:

Post.where(:author_id => Author.first)
Post.where(:author => Author.first)

PriceEstimate.where(:estimate_of_type => 'Treasure', :estimate_of_id => treasure)
PriceEstimate.where(:estimate_of => treasure)

When calling a query method on an attribute that was not selected by
an ActiveRecord query, an ActiveModel::MissingAttributeError is not
raised. Instead, a nil value is returned, which will return false once
cast to boolean.

This is undesirable, as we should not give the impression that we know
the attribute's boolean value when we haven't loaded the attribute's
(possibly) non-boolean value from the database.

This issue is present on versions going back as far as 2.3, at least.

Merged in f41dba27
[ci skip]

Since 810a50da, the new policy is to
keep old changelogs in their own branches, to avoid manual syncing
across different branches.

Please check that commit for more reasoning about the new policy.

This implements the support to encode/decode JSON
data to/from database and creating columns of type
JSON using a native type [1] supported by PostgreSQL
from version 9.2.

[1] http://www.postgresql.org/docs/9.2/static/datatype-json.html

Changes in old branches needed to be manually synched in CHANGELOGs of newer ones.
This has proven to be brittle, sometimes one just forgets this manual step.
With this commit we switch to CHANGELOGs per branch. When a new major version is
cut from master, the CHANGELOGs in master start being blank.

A link to the CHANGELOG of the previous branch allows anyone interested to
follow the history.

We reverted the removal because the new deprecation policy

This functionality will be available from gem
`active_record-session_store` instead.

reset_counters() was crashing when there were multiple belongs_to associations with the same foreign key.

This closes #5200.

For consistency with the other AR extension plugins we are creating.

ActiveRecord::ConnectionAdapters::Column#microseconds did an unnecessary
conversion to from Rational to float when calculating the integer number
of microseconds. Some terminating decimal numbers in base10 are
repeating decimal numbers in base2 (the format of float), and
occasionally this causes a rounding error.
Patch & explanation originally from Logan Bowers.