Pending work on graceful app upgrades.

Revert "Merge pull request #8439 from joshsusser/fixes"

This reverts commit ce8ac393, reversing
changes made to b0e7b6f6.

Revert "Merge pull request #8431 from joshsusser/schemadump"

This reverts commit 036d3e1c, reversing
changes made to 0c692f4d.

Revert "Merge branch 'joshsusser-master' into merge"

This reverts commit 0c692f4d, reversing
changes made to 2e299fca.

Conflicts:
	activerecord/CHANGELOG.md
	activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
	activerecord/test/cases/schema_dumper_test.rb

in the new 'variables:' hash in each database config section in database.yml.
The key-value pairs of this hash will be sent in a 'SET key = value, ...'
query on new database connections.

The configure_connection methods from mysql and mysql2 into are
consolidated into the abstract_mysql base class.

These queries don't seem to work without the includes clause. [ci skip]

The real win with these chain methods is where.not, that takes care of
different scenarios in a graceful way, for instance when the given value
is nil.

    where("author.id != ?", author_to_ignore.id)
    where.not("author.id", author_to_ignore.id)

Both where.like and where.not_like compared to the SQL versions doesn't
seem to give us that much:

    Post.where("title LIKE 'ruby on%'")
    Post.where.like(title: 'ruby on%'")
    Post.where("title NOT LIKE 'ruby on%'")
    Post.where.not_like(title: 'ruby on%'")

Thus Rails is adding where.not, but not where.like/not_like and others.

When applying default_scope to a class with a where clause, using
update_column(s) could generate a query that would not properly update
the record due to the where clause from the default_scope being applied
to the update query.

    class User < ActiveRecord::Base
      default_scope where(active: true)
    end

    user = User.first
    user.active = false
    user.save!

    user.update_column(:active, true) # => false

In this situation we want to skip the default_scope clause and just
update the record based on the primary key. With this change:

    user.update_column(:active, true) # => true

Fixes #8436.

It was pointed out by @giner that the CHANGELOG entry for https://github.com/rails/rails/commit/78d5d6f8688bb7c45ba9a3ef893682231130da3f
wasn't included. Here it is.

Sometimes, on Mac OS X, programmers accidentally press Option+Space
rather than just Space and don’t see the difference. The problem is
that Option+Space writes a non-breaking space (0XA0) rather than a
normal space (0x20).

This commit removes all the non-breaking spaces inadvertently
introduced in the comments of the code.

Closes #3313

migrated_at: timestamp when migration run
fingerprint: md5 hash of migration source
name: filename without version or extension

examples:

  Model.where.not field: nil
  #=> "SELECT * FROM models WHERE field IS NOT NULL

  Model.where.like name: 'Jeremy%'
  #=> "SELECT * FROM models WHERE name LIKE 'Jeremy%'

this feature was originally suggested by Jeremy Kemper https://github.com/rails/rails/pull/5950#issuecomment-5591330

Closes #5950

Allows you to do BaseClass.new(:type => "SubClass") as well as
parent.children.build(:type => "SubClass") or parent.build_child
to initialize an STI subclass. Ensures that the class name is a
valid class and that it is in the ancestors of the super class
that the association is expecting.

[ci skip]

Fixes #7418.

Setting a nil datetime attribute to a blank string should not cause the
attribute to be dirty.

Fix #8310

Introduced in 53ca22f2.
Thanks @rochefort. [ci skip]

Closes #8265

To perform a sum calculation over the array of elements, use to_a.sum(&block).

Please check the discussion in f9cb645d
for more context.

This reverts commit f9cb645d.

Conflicts:
	activerecord/CHANGELOG.md

Revert "Allow blocks for count with ActiveRecord::Relation. Document and test that sum allows blocks"

This reverts commit 9cc2bf69.

Conflicts:
	activerecord/lib/active_record/relation/calculations.rb

If you want to change the STI type too, use AR::Base.becomes! instead

Closes #7551

This was there due historical reasons since
7dc45818 to give the user the
possibility to create unique indexes passing "UNIQUE" as the third
argument

Closes #8104

Public method `attributes_before_type_cast` used to return internal AR structure (ActiveRecord::AttributeMethods::Serialization::Attribute), patch fixes this. Now behaves like `read_attribute_before_type_cast` and returns unserialised values.

Didn't work before because it updated the model-in-memory first, so the DB query couldn't find the record.