Overview

The standard projections are some kind of event-indexing, so you can retrieve events from all streams at once (AllStreamProjectionRunner), by category (CategoryStreamProjectionRunner) or by message name (MessageNameStreamProjectionRunner).

Installation

composer require prooph/standard-projections

Requirements

• PHP >= 7.1
• Prooph EventStore v7

AllStreamProjectionRunner

Imagine you have two streams, a stream called user and a stream called blogposts. If you are interessted in all events coming from both streams, you can use an EventStoreQuery like this:

$eventStore
    ->createQuery()
    ->fromAll()

This is slightly unperformant, especially when you have one stream per aggregate, so that you have to query thousands of streams. This is where the AllStreamProjectionRunner comes handy. It projects all events from all streams into a single large stream, so you can run queries like:

$eventStore
    ->createQuery()
    ->fromStream('$all')

CategoryStreamProjectionRunner

Let's say you use one stream per aggregate for users. So you have event streams with names: user-1, user-2 and so on. You are interested in the events from all user-streams, so your query looks like:

$eventStore
    ->createQuery()
    ->fromCategory('user')

With the CategoryStreamProjectionRunner you create a single stream for all those events. You can query it like:

$eventStore
    ->createQuery()
    ->fromStream('$ct-user')

MessageNameStreamProjectionRunner

The MessageNameStreamProjectionRunner creates a stream for each occurring message name. Let's say you have user-streams with one stream per aggregate again, and streams like user-1, user-2, and so on. You are interessted in all UserWasRegistered events, so your query looks like:

$eventStore
    ->createQuery()
    ->fromCategory('user')
    ->when(
        [
            UserWasRegistered::class => function (array $state, UserWasRegistered $event): void {
                // do something
            } 
        ]
    )

This is unperformant in two ways: First we need to query all user-streams and then we need to iterate over events, we are not interested in. With the MessageNameStreamProjectionRunner your query would look like:

$eventStore
    ->createQuery()
    ->fromStream('$mn-UserRegistered')

Usage

The runners are expected to run in a simple CLI script. As it's framework agnostic, you have to provide these cli-scripts yourself. This is how they basically look like:

<?php

$container = require 'container.php';

$projectionManager = $container->get(\Prooph\EventStore\Projection\ProjectionManager::class);

$runner = new \Prooph\StandardProjections\AllStreamProjectionRunner($projectionManager);
$runner();