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Merge pull request #16361 from JackDanger/clearer-connection-pool-doc…

…umentation

[doc] Clarify how the ConnectionHandler works
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commit 0361a6a3d20d2742ac73f2fb6c1a904564c2327c 2 parents 639a2e7 + 38be633
Rafael Mendonça França rafaelfranca authored
51 activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
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@@ -462,23 +462,44 @@ def checkout_and_verify(c)
#
# For example, suppose that you have 5 models, with the following hierarchy:
#
- # |
- # +-- Book
- # | |
- # | +-- ScaryBook
- # | +-- GoodBook
- # +-- Author
- # +-- BankAccount
+ # class Author < ActiveRecord::Base
+ # end
#
- # Suppose that Book is to connect to a separate database (i.e. one other
- # than the default database). Then Book, ScaryBook and GoodBook will all use
- # the same connection pool. Likewise, Author and BankAccount will use the
- # same connection pool. However, the connection pool used by Author/BankAccount
- # is not the same as the one used by Book/ScaryBook/GoodBook.
+ # class BankAccount < ActiveRecord::Base
+ # end
#
- # Normally there is only a single ConnectionHandler instance, accessible via
- # ActiveRecord::Base.connection_handler. Active Record models use this to
- # determine the connection pool that they should use.
+ # class Book < ActiveRecord::Base
+ # establish_connection "library_db"
+ # end
+ #
+ # class ScaryBook < Book
+ # end
+ #
+ # class GoodBook < Book
+ # end
+ #
+ # And a database.yml that looked like this:
+ #
+ # development:
+ # database: my_application
+ # host: localhost
+ #
+ # library_db:
+ # database: library
+ # host: some.library.org
+ #
+ # Your primary database in the development environment is "my_application"
+ # but the Book model connects to a separate database called "library_db"
+ # (this can even be a database on a different machine).
+ #
+ # Book, ScaryBook and GoodBook will all use the same connection pool to
+ # "library_db" while Author, BankAccount, and any other models you create
+ # will use the default connection pool to "my_application".
+ #
+ # The various connection pools are managed by a single instance of
+ # ConnectionHandler accessible via ActiveRecord::Base.connection_handler.
+ # All Active Record models use this handler to determine the connection pool that they
+ # should use.
class ConnectionHandler
def initialize
# These caches are keyed by klass.name, NOT klass. Keying them by klass
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