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Rails initializers
By default, Rails loads Zeitwerk after the initializers in config/initializers are loaded.
Autoloading before Zeitwerk is loaded is now deprecated but because we use a lot of autoloaded
constants in our initializers, we had to move the loading of Zeitwerk earlier than these
initializers.
A side-effect of this is that in the initializers, config.autoload_paths is already frozen.
To run an initializer before Zeitwerk is loaded, you need put them in config/initializers_before_autoloader.
Ruby files in this folder are loaded in alphabetical order just like the default Rails initializers.
Some examples where you would need to do this are:
- Modifying Rails'
config.autoload_paths - Changing configuration that Zeitwerk uses, for example, inflections
Database connections in initializers
Ideally, database connections are not opened from Rails initializers. Opening a
database connection (for example, checking the database exists, or making a database
query) from an initializer means that tasks like db:drop, and
db:test:prepare will fail because an active session prevents the database from
being dropped.
To help detect when database connections are opened from initializers, we now
warn in STDERR. For example:
DEPRECATION WARNING: Database connection should not be called during initializers (called from block in <module:HasVariable> at app/models/concerns/ci/has_variable.rb:22)
If you wish to print out the full backtrace, set the
DEBUG_INITIALIZER_CONNECTIONS environment variable.