Phazor.Reactive 1.0.63

Phazor.Reactive

A package that allows to define and generate reactive entities and events to use in Blazor applications with Phazor components.

Idea

Reactive components are useful when you want your UI to respond to some state changes in the application. Such components are often represent some entities in your application, so, if you want to represent entity state reactively – your entities must also be reactive.

In .NET and Blazor realities, for entity to be reactive means that it's data should be represented as IObservable, so your code can subscribe to its data changes. Hand rolling a reactive entity is not that hard, but, as number of entities and their properties grow, it can become complex and challenging to maintain.

This is when Phazor.Reactive comes into play. It provides abstractions to describe your reactive entities, events that can affect them as well as source generators, that implement all the entities and event handlers. When using this library, creating reactive entities and their behaviour boils down to defining interfaces and describing what effects are made by events.

Glossary

• Reactive entity (entity) – an interface that derives from IReactiveEntity<TIdentifier>
• Reactive event (event) – a type that implements IReactiveEvent<TSelf> and describes how it should be handled
• Effect – a part of event handling description, that results to entity change
• Entity factory – an abstraction used to create entity instances

Defining an entity

In Phazor.Reactive concept, a reactive entity is a binding to some instance of an entity. What does that mean? As all the state of an entity is reactive, you do not need all the data to create it, it can be acquired later with events. The only required data is its identity – identifier. So, being a binging means that it represents an instance which data may not be loaded yet, but it will be there eventually.

As Phazor.Reactive generates an implementations for your entities, reactive entities are defined as interfaces, that derive from IReactiveEntity<TIdentifier>. Base interface itself provides an TIdentifier Id property.

public interface IMyEntity : IReactiveEntity<long>;

Reactive properties

To define reactive state you must add a property with IObservable<> type, Phazor.Reactive also allows for reactive collection properties with IObservable<IEnumerable<>> type (no other collection type is supported). These properties must be defined with get accessor only.

public interface IMyEntity : IReactiveEntity<long>
{
    IObservable<int> Value { get; }
    
    IObservable<IEnumerable<string>> Collection { get; }
}

Behind the scenes, Phazor.Reactive will generate implementation for this type, wiring all the observables. The library will only generate observable properties in the implementation, but if you need to implement any custom properties or methods, you can add them by creating another part of a class as it is generated as partial.

Defining your own parts

As Phazor.Reactive generates entity classes as partial, you can define your own parts of implementation (for example for implementing some logic). In case of you needing some additional state (some services for example) you can add a custom constructor in your part of an entity. Be aware that in that case, the library won't generate a constructor, so you would have to initialize Id property manually.

All the parameters beside the id will be injected from DI, see factory section for more info.

Reactive events

After you defined your reactive entity, you need some way to update its state, and this (and only) way to do that is reactive events. Reactive event is a type, that implements an IReactiveEvent<TSelf> interface. Event can be of any type – class, struct, record, record struct. This interface requires you to implement a single method to describe how event should be handled.

public record MyEvent(long Id, int Value) : IReactiveEvent<MyEvent>
{
    public static void Handle(ReactiveEventHandler<MyEvent> handler) { }
}

This method has a single argument of type ReactiveEventHandler<> that is used to describe which effects event has on an application state. This type is abstract, and does not have any implementations, its method calls will be used by generators.

Defining an effect requires several method calls:

1. Selecting affected entity using .Affects<TEntity, TIdentifier> method
2. Specifying entity selector using .SelectedBy method. This method accepts an expression that gets an identifier value from event
3. Selecting entity property using .AndItsProperty method. This method accepts an expression that gets a property from entity. You should only pass a simple member access expressions to this method.

public static void Handle(ReactiveEventHandler<MyEvent> handler)
{
    handler
        .Affects<IMyEntity, long>()
        .SelectedBy(x => x.Id)
        .AndItsProperty(x => x.Collection);
}

After you specify a target for your event effect, you have to specify the effect itself. There are two kind of effects: property effects and collection property effects.

Property effects

A property effect is an effect on non-collection property. This kind of effect allows only changing property value, it may be interpreted as a setter of some sort.

To define a property effect, you should select a non-collection property and call .ByChangingTo method. This method accepts an expression that gets a value from event.

public static void Handle(ReactiveEventHandler<MyEvent> handler)
{
    handler
        .Affects<IMyEntity, long>()
        .SelectedBy(x => x.Id)
        .AndItsProperty(x => x.Value)
        .ByChangingTo(x => x.Value);
}

Collection effects

Collection effects are effects on collection properties (ei IObservable<IEnumerable<>> properties). This kind of effect allows several collection transformation

• Add value: using .ByAdding method. This method accepts an expression that gets either a single value or collection from event.
• Remove value: using .ByRemoving method. This method accepts an expression that gets either a single value or collection from event.
• Replace values: using .ByReplacingWith method. This method accepts an expression that gets either single value or collection from event.
• Clear values: using .ByClearing method.

public static void Handle(ReactiveEventHandler<MyEvent> handler)
{
    handler
        .Affects<IMyEntity, long>()
        .SelectedBy(x => x.Id)
        .AndItsProperty(x => x.Collection)
        .ByAdding(x => x.Value);
}

Event handlers

When you define an event and its effects, Phazor.Reactive will generate a handler for it. This handler will execute all configured effects. Handlers must be registered in IServiceCollection, method for it is also generated by the library.

Entity factories

Entity factories are used to create entity instances. They cache entity objects, meaning every time that you create instances with same id, you will get same object. These factories are used internally in event handler implementations, but you also can and should use them to gain access to reactive entities.

Factories are presented with IReactiveEntityFactory<TEntity, TIdentifier> interface, its implementation is generated by the library. You can use a .Create method that accepts an identifier and returns an instance of entity.

Factories must be registered in IServiceCollection, method for it is also generated by library.

Factories for partial entities

When you have defined a part of entity with a custom constructor, all its parameters (except for id) will be taken from DI. Library will generate a fields and constructor for all these parameters.

Event publishers and providers

To work with events you can use IReactiveEventPublisher and IReactiveEventProvider interfaces.

Publisher allows you to send events to handlers, which will run registered effects. To publish event use .PublishAsync method.

You can also observe and handle events manually, not with entities. To do that, use .Observe<TEvent> method on event provider.

Registration

To register Phazor.Reactive in ServiceCollection call a .AddPhazorReactive extension method on it. It will register all the basic implementations for the library.This method accepts a single argument a delegate action on IPhazorReactiveConfigurator object. This configurator allows you to register an event handlers and entity factories.

Phazor.Reactive generates an extension method on IPhazorReactiveConfigurator to register all generated types. This generated method has name schema AddPhazorReactiveFrom{AssemblyName} with assembly name without dots (ex: AddPhazorReactiveFromMyReactiveApp, for My.Reactive.App)

collection.AddPhazorReactive(reactive => reactive
    .AddPhazorReactiveFromMyReactiveApp());