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Nested Structures

Most of the time, your model for a view will not be of a simple data-type or a List, but a complex entity, like a person having a name, multiple addresses, an email, a date of birth, etc.

In those cases, you will most likely need Stores for the single properties of your main entity, and - later on - for the properties of the sub-entity like the street in an address in our example from above.

fritz2 uses a mechanism called Lens to describe the relationship between an entity and its sub-entities and properties. So before you continue, please make yourself familiar with Lenses in fritz2.

Having a Lens available which points to some specific property makes it very easy to get a SubStore for that property from a Store of the parent entity:

    val outerStore = storeOf(Outer(Inner("hello"), "world"))
    // remember, the L-object is created by fritz2-gradle-plugin per package
    val innerStore = outerStore.sub(L.Outer.inner)

Now you can use your innerStore exactly like any other Store to set up two-way-databinding, call sub(...) again to access the properties of Inner. If a SubStore contains a List, you can of course iterate over it by using each() or eachStore() like you are used to. It’s fully recursive from here on down to the deepest nested parts of your model.

You can also add Handlers to your SubStores by simply calling the handle-method:

val booleanSubStore = mainStore.sub(someLens)
val switch = booleanSubStore.handle { model: Boolean ->
   !model
}

render {
    ...
        button {
            text("switch state")
            clicks handledBy switch
        }
    ...
}

To keep your code well-structured, it is recommended to implement complex logic at your RootStore or inherit it by using interfaces. However, the code above is a decent solution for small (convenience-)handlers.

Now you can handle all kinds of data and structures in your Stores. Next you might want to check, if your model is valid. In fritz2 this is done by Validation.


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