debian-mirror-gitlab/doc/development/rails_initializers.md

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---
stage: none
group: unassigned
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info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/product/ux/technical-writing/#assignments
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---
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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:
1. Modifying Rails' `config.autoload_paths`
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1. Changing configuration that Zeitwerk uses, for example, inflections
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## Database connections in initializers
Ideally, database connections are not opened from Rails initializers. Opening a
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database connection (for example, checking the database exists, or making a database
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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.
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To prevent this, we stop database connections from being opened during
routes loading. Doing will result in an error:
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```shell
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RuntimeError:
Database connection should not be called during initializers.
# ./config/initializers/00_connection_logger.rb:15:in `new_client'
# ./lib/gitlab/database/load_balancing/load_balancer.rb:112:in `block in read_write'
# ./lib/gitlab/database/load_balancing/load_balancer.rb:184:in `retry_with_backoff'
# ./lib/gitlab/database/load_balancing/load_balancer.rb:111:in `read_write'
# ./lib/gitlab/database/load_balancing/connection_proxy.rb:119:in `write_using_load_balancer'
# ./lib/gitlab/database/load_balancing/connection_proxy.rb:89:in `method_missing'
# ./config/routes.rb:10:in `block in <main>'
# ./config/routes.rb:9:in `<main>'
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```