Conversion Playbook
Incrementally modernize your Relay Classic app in these steps:
Step 0: Install and configure your environment
Follow the steps outlined in the Migration Setup guide.
Step 1: Incrementally convert to Relay Compat
Start converting your components and mutations to use the Relay Modern APIs from the 'react-relay/compat' module (createFragmentContainer, createRefetchContainer, createPaginationContainer, commitMutation). It will be easier to go from the leaf components up. The conversion scripts should make this step less tedious.
If a fragment uses variables that are determined at runtime, see below.
Step 2: Introduce
Once all the components and mutations have been converted to use the Relay Modern APIs, convert to using QueryRenderer instead of using Relay.Renderer or Relay.RootContainer. You may supply Store from 'react-relay/classic' as the environment for most cases.
Step 3: Introduce Relay Modern runtime
Once a few or all of your views are using QueryRenderer, Store from 'react-relay/classic' could be replaced with a RelayModernEnvironment. Keep in mind that RelayModernEnvironment and Store do not share any data. You might want to hold off on this step until views that have significant data overlap can be switched over at the same time. This step is what unlocks the perf wins for your app. Apps using the RelayModernEnvironment get to send persisted query IDs instead of the full query strings to the server, as well as much more optimized data normalizing and processing.
Step 4: Clean up by replacing Relay Compat with Relay Modern.
Switch the 'react-relay/compat' references in your app to 'react-relay'. This is more of a clean-up step that prevents your app from pulling in unnecessary 'react-relay/classic' code.
Note: Determining variable values at runtime
There is currently only one supported way to set the initial value of a variable dynamically: using global variables defined on the query that includes the fragment (or via variables on the QueryRenderer).
For example, if currentDate is set in QueryRenderer variables, then $currentDate may be referenced in any fragment included in the QueryRenderer query.
If you're using createRefetchContainer then your refetch method may also update these variables to render with new values.