The realtime module is responsible to propagate database changes to the concerned clients in realtime. The clients execute a
liveQuery which is similar to a normal query with a where clause. The realtime module makes sure that whenever there is any change in the result set (results get added, removed or updated), the client will be updated.
How it works?
The realtime module guarantees that all changes will propagate to the client irrespective of failures on the backend. To achieve these guarantees, Space Cloud uses Apache Kafka under the hood.
However, Space Cloud doesn't use Kafka by default. It uses Kafka ony when the
PROD environment variable is set to true or when
space-cloud is started with the
Note: The distributed mode of realtime module is not implemented yet.
There are a few limitations in the queries which can be used while using the realtime module.
- The primary key must be
_idin case of MongoDB and
idfor MySQL and Postgres and of type
- All documents to be inserted must have the
_id(for MongoDB) or
id(for MySQL and Postgres) fields set.
- The fields used in the where clause of
liveQueryshould not be updated by another request.
- All updates and deletes can be made on a single document only using the
idfield in the where clause.
Enable the realtime module
The configuration pertaining to the realtime module can be found under the
realtime key under the
modules object. Here's a snippet showing how to enable the realtime module. This 3 line snippet will set up all the necessary routines required by the realtime module.
modules: realtime: enabled: true # Enable the realtime module globally kafka: localhost # Connection string for kafka # Config for other modules go here
You also need to to enable the feature on the collections you want to sync. Here's a snippet which indicates that the collection
todos is realtime.
modules: crud: mongo: conn: mongodb://localhost:27017 isPrimary: true collections: todos: isRealtimeEnabled: true # This makes the todos collection realtime rules: create: rule: allow read: rule: allow update: rule: allow delete: rule: allow realtime: enabled: true # Enable the realtime module globally kafka: localhost # Config for other modules go here
That's all you need to do to enable the realtime module. It's time to go ahead and how to use the realtime module on the frontend.