projection.md

id	title
projection	Projection

:::info TypeScript Support

A read model projection has an associated TypeScript type:

• Type Name - ReadModel
• Package - @resolve-js/core

:::

A read model projection is an object of the following structure:

const projection = {
  // The *Init* function initializes the read model's persistent store.
  Init: async (store) => { ... }
  // An event handler function is associated with an event type.
  // It receives the read model store and an incoming event
  // and updates the store based on the event's data.
  [EVENT_TYPE1]: async (store, event, context) -> { ... }
  [EVENT_TYPE2]: async (store, event, context) -> { ... }
}

An event handler implementation receives the following arguments:

Argument Name	Description
store	Exposes API used to communicate with the read model's persistent data storage.
event	An object that contains the incoming event's data.
context	An object that contains data and functions related to the current operation.

context

The context argument is an object with the following fields:

Field Name	Description
encrypt	The user-defined encrypt function.
decrypt	The user-defined decrypt function.

This object can also contain additional fields added by middleware.