Projections api

[joelhoisko]

• Added a new package projections in the project.
• New client.withProjections() for building Projections inline
• New ProjectionsBuilder with createProjection(projectionId) method that returns a ProjectionBuilder that has 3 methods:
  • inScope(scopeId) for setting the scope (defaults to default scope)
  • forReadModel(Constructor<any>) that takes a class to register as a readmodel for the projection
  • on() with all of the variations for using EventTypes, type arguments or Generations etc
• I made the API a bit more flat so that you can put the forReadModel(), on() and inScope() methods in whichever order.
  • I don't think we need a constraint on this, if users want to put them in a different order then that's on them. It also doesn't make the code suddenly stop working if you put forReadModel() before inScope() or stuff like that.
  • This also means that the code is more error prone as it's slightly easier to accidentally call forReadModel() twice I guess. This gets checked during the build and it will throw an error in that case.
• New sample in Samples/Tutorials/Projections with a readmodel of all chefs and all the dishes they've prepared
  • This could be enough for the tutorial too, that can be discussed when we get there
• Code regarding the decorators is not complete as we should just first focus on the inline
• The projections project builds, but the whole repo doesn't as I'm waiting for the ProjectionsClient from the new contracts for JS. I've mocked the ProjectionsClient in places with a dummy type.
• You can delete a readmodel by returning a ProjectionResult.delete in the on() method.

Example how the inline code would look like:

const client = Client
    .forMicroservice('f39b1f61-d360-4675-b859-53c05c87c0e6')
    .withEventTypes(eventTypes => {
        eventTypes.register(DishPrepared);
        eventTypes.register(ChefFired);
    })
    .withProjections(projections => {
        projections.createProjection('4a4c5b13-d4dd-4665-a9df-27b8e9b2054c')
            .forReadModel(Chef)
            .on(DishPrepared, _ => _.keyFromProperty('Chef'), (chef, event, ctx) => {
                console.log(`Handling event ${JSON.stringify(event)} and read model ${JSON.stringify(chef)}`);
                chef.name = event.Chef;
                chef.dishes.push(event.Dish);
                return chef;
            })
            .on(ChefFired, _ => _.keyFromProperty('Chef'), (chef, event, ctx) => {
                console.log(`Firing ${chef.name}`);
                return ProjectionResult.delete;
            })
        })
    .build();

And a diagram on how the builder works:

[joelhoisko]

This one is still missing lots of stuff, I've been just kinda copying our structure for event handlers and making it "seemingly" fit the projections stuff we've been thinking about. No samples or building code yet.