resolve-query

Provides an interface for creating and querying Read- and View-Models.

A Read Model is an application state built from the Event Log by Projection Functions and used to reply to Queries. It can be saved into a server-side Storage using an appropriate Storage Adapter. Queries to a Read Model are processed by Resolver Functions, which can filter, aggregate and/or paginate data before sending it to the client side. You can manage the Resolver behavior using client-defined arguments. Read Models can be reactive. In this case, the server-side changes trigger the client-side updates.

A View Model is built on the client side and used to keep the UI up to the current application state. It is built and updated by Reducers. Aggregates whose events should participate in the View Model construction are defined by the aggregateId (in most cases, one aggregate corresponds to one view model, although, a wildcard aggregateId is possible).

import { createReadModel, createViewModel } from 'resolve-query'

Usage

Pass the following arguments to the createReadModel factory function to create a Read Model:

• eventStore - A configured eventStore instance.
• projection - An object with Projection Functions used to handle incoming Events and build the Read Model.
• adapter - A Read Model adapter instance. A memory adapter, which supports a simple query & projection API is used by default.
• resolvers - An object with Resolver Functions. Each function should accept two arguments: the first argument is a reference to the target Read Model. The second argument is an object with fields used to extract data from a Read Model Storage.

A Read Model supports the following functions to query data:

• read - Performs a query within a Read Model via Resolvers. The first argument is a Resolver name; the second one contains an object with the Resolver function properties. Returns the Resolver execution result.
• makeReactiveReader - Creates reactive Read Models. The first argument is a callback for publishing changes; the following are equivalent to the read function arguments. Returns the { result, forceStop } object, where result is the first Resolver execution result, and forceStop is a function used to stop publishing Read Model changes.
• getLastError - Returns the last error that occurred while applying events by adapter-bound projection functions.
• getReadInterface - Returns the underlying Read-Side Storage API object after it has been initialized. Can be used for direct read-only interactions with the Read-Model Storage.
• dispose - Removes the Read Model. Invokes the Read Model Adapter's disposal mechanisms and stops listening to the Event Store bus. The default adapters' disposal operation disconnects with the storage and drops stored tables.

Pass the following arguments to the createViewModel factory function to create a View Model:

• eventStore - A configured eventStore instance.
• projection - A map of Redux-like Reducer functions. A function per each event type.
• snapshotAdapter - An adapter for loading and saving the intermediate Aggregate state. The argument is optional, snapshots are not used by default.
• snapshotBucketSize - Number of events between storing an aggregate snapshot. Argument is optional, the default value is 100.

You can access Resolvers and query data from Read Models using a Facade, which supports the following functions:

• read - Performs a query from a View Model using Resolvers.
• dispose - Deletes the View Model (for internal use).

Example

See the Top List example.