Fix small typo in configuring guide [skip ci]

Update Engine getting started generation instructions for consistency

New to Rails but looks like everything for an engine should be done inside the engine's folder. The updated text has been there for a long time so I hope I'm not just missing something. At this point in the example the user does not have an application (that comes in the next section) and elsewhere in the doc there is talk of the importance of running the commands from the *engine* root so it seems more consistent to talk about "engine root" as updated.

Combine and deprecate `rails db:structure:{dump,load}` tasks into `rails db:schema:{dump,load}`

Update outdated bundler in gemspec

Use headings to make Action Cable terminology more clear [skip ci]

The Terminology section of the Action Cable guide currently is one large
text without any headings. Instead of having one large text, we can use
headings to describe all terminology for easier scanability and improved
table of contents.

The Broadcastings section mentions Pub/Sub so it's moved beneath the Pub/Sub
section.

The following part is moved up to the Connections terminology section.
It makes more sense to have it where it introduces the term.
> Connections form the foundation of the client-server relationship.

Refer to channel instead of cable [ci-skip]

Merge pull request #39886 from lanzhiheng/append-some-description-about-advance-constraints-in-block-form

 [ci skip] Append some description about advance constraints

Automatically set Link header for each stylesheet and script

Fix eager loading that non-select columns will be loaded

Fix preloader to associate preloaded records by default

Related to #35210.

We sometimes use `select` to limit unused columns for performance.

For example, `GET /posts/1` (post detail) usually use (almost) all
columns, but `GET /posts` (post list) does not always use all columns
(e.g. use `id` and `title` for the list view, but `body` is not used).

If an association is eager loaded, the limited `select` doesn't works as
expected, eager loading will load all columns on the model, plus also
load the `select` columns additionally. It works differently with
natural load and preload. It means that changing natural load or preload
to eager load (or vice versa) is unsafe.

This fixes eager loading that always load all columns (plus extra
`select` columns), to respect the `select` columns like as others.

```ruby
post = Post.select("UPPER(title) AS title").first
post.title # => "WELCOME TO THE WEBLOG"
post.body  # => ActiveModel::MissingAttributeError

# Rails 6.0 (ignore the `select` values)
post = Post.select("UPPER(title) AS title").eager_load(:comments).first
post.title # => "Welcome to the weblog"
post.body  # => "Such a lovely day"

# Rails 6.1 (respect the `select` values)
post = Post.select("UPPER(title) AS title").eager_load(:comments).first
post.title # => "WELCOME TO THE WEBLOG"
post.body  # => ActiveModel::MissingAttributeError
```

Someone had relied on the behavior that preloading with a given scope,
but the behavior has lost in #35496 to fix the minor bug that unloading
through association.

Basically we don't guarantee the internal behavior, but the bugfix can
be achieved without any breaking change, so I've restored the lost
functionality.

Fixes #36638.
Fixes #37720.

fix(guides): Update AWDwR book link in Releasing Rails guide [ci skip]

Use superclass name in inspect of anonymous ActionView::Base subclass

When rendering views an anonymous subclass is created by calling
ActionView::Base.with_empty_template_cache.
This causes inspect to return an unhelpful description when calling
inspect:
`#<#<Class:0x012345012345>:<0x012345012345>`.

This can be confusing when exceptions are raised because it's hard to
figure out where to look. For example calling an undefined method in a
template would raise the following exception:

    undefined method `undefined' for #<#<Class:0x012345012345>:<0x012345012345>

Instead we can return the non-anonymous superclass name.

    undefined method `undefined' for #<ActionView::Base:0x01234502345>

The anonymous class is created in ActionView::Base.with_empty_template_cache.
See f9bea630
This seems to be done for performance reasons only, without expecting a
change to calling `inspect`.

Remove double negative in testing docs [ci-skip]

Update guides/source/testing.md
Co-authored-by: NJonathan Hefner <jonathan@hefner.pro>

Fix incorrect result when eager loading with duplicated through association with join scope Part 2

Fix spelling of DigitalOcean in docs [ci-skip]

Fixes the spelling of DigitalOcean in the ActiveStorage guide.

Remove unnecessary `compact`

Looking at the history this is holdover from the pre-pool manager and
changes made by Shopify. The tests pass without it and we've had enough
changes that it doesn't appear necessary anymore.
Co-authored-by: NJohn Crepezzi <john.crepezzi@gmail.com>

Merge pull request #40048 from eileencodes/fix-incorrect-removal-of-current_shard-from-establish_connection

Fix incorrect removal of current_shard in establish_connection

If we enter a `connected_to` block and call `establish_connection` like
the test added here we need to ensure that `shard: current_shard` is passed
to the handler, otherwise the connection will be established on
`default` not on `shard_one`.
Co-authored-by: NJohn Crepezzi <john.crepezzi@gmail.com>

Rename test models for inclusivity

After renaming `Man` to `Human` the variable letter `m` in these tests
ends up being pretty confusing. Rather than rename it to `h`, this
commit replaces it with the full word `human`.

Since I was already renaming things, I also went ahead and replaced `f`
with `face`, `i` with `interest`, and `a` with `author`.

The commit replaces the `Man` model used in tests with a `Human` model. It
also replaces the existing `Human` model with a `SuperHuman` model
inheriting from `Human`.

While this may seem like a cosmetic change, I see it as more of an
inclusivity change. I think it makes sense for a number of reasons:

* Prior to this commit the `Human` model inherited from `Man`. At best
  this makes no sense (it should be the other way around). At worst it
  is offensive and harmful to the community.
* It doesn't seem inclusive to me to have exclusively male-gendered
  examples in the codebase.
* There is no particular reason for these examples to be gendered.
* `man` is hard to grep for, since it also matches `many, manager,
  manual, etc`

For the most part this is a simple search and replace. The one exception
to that is that I had to add the table name to the model so we could use
"humans" instead of "humen".

Follow up of #40000.

In #40000, `eager_load(:general_categorizations, :general_posts)` works,
but `eager_load(:general_posts, :general_categorizations)` doesn't work
yet.

This implements the deduplication for the case of reversed eager loading
order.

Follow-up to #40013.

Newly created `Blob`s may not be uploaded yet, so do not try to update
their service metadata.

Adds documentation for habtm association always being optional: true [ci skip]

parent f4471fc7
author Sandip Mane <sandip.mane@bigbinary.com> 1593247595 +0530
committer Sandip Mane <sandip2490@gmail.com> 1597253412 +0530

Adds doc for habtm association for always optional: true

Added docs line under definition of habtm with a text containing habtm refers to zero or more associations

Added docs line under definition of habtm with a text containing it refers to zero or more associations

Updated the sentence to include declaring association for habtm relation

Add baseline defaults section [ci skip]