Encapsulating data with DataObject

In the previous section we introduced distributed data structures and demonstrated how to use them. We’ll now discuss how to combine those distributed data structures with custom code (business logic) to create modular, reusable pieces.

The Aqueduct is a library for building Fluid objects and Fluid containers within the Fluid Framework. Its goal is to provide a thin base layer over the existing Fluid Framework interfaces that allows developers to get started quickly.

Fluid object development

Fluid object development consists of developing the data object and the corresponding data object factory. The data object defines the logic of your Fluid object, whereas the data object factory defines how to initialize your object.

Data object development

DataObject and PureDataObject are the two base classes provided by the library.

DataObject

The DataObject class extends PureDataObject and provides the following additional functionality:

  • A root SharedDirectory that makes creating and storing distributed data structures and objects easy.
  • Blob storage implementation that makes it easier to store and retrieve blobs.

Note: Most developers will want to use the DataObject as their base class to extend.

PureDataObject

PureDataObject provides the following functionality:

  • Basic set of interface implementations to be loadable in a Fluid container.
  • Functions for managing the Fluid object lifecycle.
    • initializingFirstTime(props: S) - called only the first time a Fluid object is initialized and only on the first client on which it loads.
    • initializingFromExisting() - called every time except the first time a Fluid object is initialized; that is, every time an instance is loaded from a previously created instance.
    • hasInitialized() - called every time after initializingFirstTime or initializingFromExisting executes
  • Helper functions for creating and getting other data objects in the same container.

Note: You probably don’t want to inherit from this data object directly unless you are creating another base data object class. If you have a data object that doesn’t use distributed data structures you should use Container Services to manage your object.

DataObject example

In the below example we have a simple data object, Clicker, that will render a value alongside a button the the page. Every time the button is pressed the value will increment. Because this data object renders to the DOM it also extends IFluidHTMLView.

export class Clicker extends DataObject implements IFluidHTMLView {
    public static get Name() { return "clicker"; }

    public get IFluidHTMLView() { return this; }

    private _counter: SharedCounter | undefined;

    protected async initializingFirstTime() {
        const counter = SharedCounter.create(this.runtime);
        this.root.set("clicks", counter.handle);
    }

    protected async hasInitialized() {
        const counterHandle = this.root.get<IFluidHandle<SharedCounter>>("clicks");
        this._counter = await counterHandle.get();
    }

    public render(div: HTMLElement) {
        ReactDOM.render(
            <CounterReactView counter={this.counter} />,
            div,
        );
        return div;
    }

    private get counter() {
        if (this._counter === undefined) {
            throw new Error("SharedCounter not initialized");
        }
        return this._counter;
    }
}

DataObjectFactory development

The DataObjectFactory is used to create a Fluid object and to initialize a data object within the context of a Container. The factory can live alongside a data object or within a different package. The DataObjectFactory defines the distributed data structures used within the data object as well as any Fluid objects it depends on.

The Aqueduct offers a factory for each of the data objects provided.

More details

DataObjectFactory example

In the below example we build a DataObjectFactory for the <code>Clicker</code> example above. To build a DataObjectFactory, we need to provide factories for the distributed data structures we are using inside of our DataObject. In the above example we store a handle to a SharedCounter in this.root to track our "clicks". The DataObject comes with the SharedDirectory (this.root) already initialized, so we just need to add the factory for SharedCounter.

export const ClickerInstantiationFactory = new DataObjectFactory(
    Clicker.Name,
    Clicker,
    [SharedCounter.getFactory()], // distributed data structures
    {}, // Provider Symbols see below
);

This factory can then create Clickers when provided a creating instance context.

const myClicker = ClickerInstantiationFactory.createInstance(this.context) as Clicker;

Providers in data objects

The this.providers object on PureDataObject is initialized in the constructor and is generated based on Providers provided by the Container. To access a specific provider you need to:

  1. Define the type in the generic on PureDataObject/DataObject
  2. Add the symbol to your factory (see DataObjectFactory Example below)

In the below example we have an IFluidUserInfo interface that looks like this:

interface IFluidUserInfo {
    readonly userCount: number;
}

On our example we want to declare that we want the IFluidUserInfo Provider and get the userCount if the Container provides the IFluidUserInfo provider.

export class MyExample extends DataObject<IFluidUserInfo> {
    protected async initializingFirstTime() {
        const userInfo = await this.providers.IFluidUserInfo;
        if(userInfo) {
            console.log(userInfo.userCount);
        }
    }
}

// Note: we have to define the symbol to the IFluidUserInfo that we declared above. This is compile time checked.
export const ClickerInstantiationFactory = new DataObjectFactory(
    Clicker.Name
    Clicker,
    [], // distributed data structures
    {IFluidUserInfo}, // Provider Symbols see below
);

Container development

A Container is a collection of data objects and functionality that produce an experience. Containers hold the instances of data objects as well as defining the data objects that can be created within the Container. Because of this data objects cannot be consumed except for when they are within a Container.

The Aqueduct library provides the <code>ContainerRuntimeFactoryWithDefaultDataStore</code> that enables you as a container developer to:

Container object example

In the below example we will write a Container that exposes the above <code>Clicker</code> using the <code>Clicker Factory</code>. You will notice below that the Container developer defines the registry name (data object type) of the Fluid object. We also pass in the type of data object we want to be the default. The default data object is created the first time the Container is created.

export fluidExport = new ContainerRuntimeFactoryWithDefaultDataStore(
  ClickerInstantiationFactory.type, // Default data object type
  ClickerInstantiationFactory.registryEntry, // Fluid object registry
  [], // Provider Entries
  [], // Request Handler Routes
);

Provider entries development

The container developer can optionally provide a registry of ProviderEntry objects into the container. A ProviderEntry is defined as follows:

interface ProviderEntry<T extends keyof IFluidObject> {
    type: T;
    provider: FluidProvider<T>
}

The type must be a keyof IFluidObject. This basically means that it needs to be the name of an interfaces that extends off of IFluidObject. The provider must be something that provides the interface defined in type. The DependencyContainer we use in the @fluidframework/synthesize package defines the following FluidObjectProvider types:

type FluidObjectProvider<T extends keyof IFluidObject> =
    IFluidObject[T]
    | Promise<IFluidObject[T]>
    | ((dependencyContainer: DependencyContainer) => IFluidObject[T])
    | ((dependencyContainer: DependencyContainer) => Promise<IFluidObject[T]>);
IFluidObject[T]

An object that implements the interface.

Promise<IFluidObject[T]>

A Promise to an object that implements the interface

(dependencyContainer: DependencyContainer) => IFluidObject[T]

A factory that will return the object.

(dependencyContainer: DependencyContainer) => Promise<IFluidObject[T]>

A factory that will return a Promise to the object.

Container-level request handlers

You can provide custom request handlers to the container. These request handlers are injected after system handlers but before the DataObject get function. Request handlers allow you to intercept requests made to the container and return custom responses.

Consider a scenario where you want to create a random color generator. I could create a RequestHandler that when someone makes a request to the Container for {url:"color"} will intercept and return a custom IResponse of { status:200, type:"text/plain", value:"blue"}.

We use custom handlers to build the Container Services pattern.