Connecting stores to each other

Most real-world applications contain multiple stores which need to be linked to properly react to model changes.

To make your stores interconnect, fritz2 allows calling Handlers of others stores directly with or without a parameter.

object SaveStore : RootStore<String>("") {
    val save = handle<String> { _, data -> data }
}

object InputStore : RootStore<String>("") {
    val input = handle<String> { _, input -> SaveStore.save(input) }
}

In cases where you don’t know which Handler of another store will handle the exposed data, you can use the EmittingHandler, a type of handler that doesn’t just take data as an argument but also emits data on a new Flow for other handlers to receive.

Create such a handler by calling the handleAndEmit<T>() function instead of the usual handle() function and add the offered data type to the type brackets:

val personStore = object : RootStore<Person>(Person(...)) {
    val save = handleAndEmit<Person> { person ->
        emit(person) // emits current person
        Person(...) // return a new empty person (set as new store value)
    }
}

The EmittingHandler named save emits the saved Person on its Flow. Another store can be setup to handle this Person by connecting the handlers:

val personStore = ... //see above

val personListStore = object : RootStore<List<Person>>(emptyList<Person>()) {
    val add = handle<Person> { list, person ->
       console.log("add new person: $person")
       list + person
    }

    init {
       // don't forget to connect the handlers
       personStore.save handledBy personListStore.add
    }
}

After connecting these two stores via their handlers, a saved Person will also be added to the list in personListStore. All depending components will be updated accordingly.

To see a complete example visit our validation example which uses connected stores and validate a Person before adding it to a list of Persons.

Most of the time you will work on much more complex structures in your data model, so you will need to get Stores for elements “hidden” deeper in your Nested Structures. Let’s see how fritz2 can help you here.