Resolve-query NPM

resolve-query

Provides an interface for creating read and view models and query facade for them.

Queries are used to observe a system 's state. Read Models answer Queries and are built using Projection functions. All events from the beginning of time are applied to a Read Model to build its current state (or a state at a particular moment in time if necessary). Some Read Models, called View Models, are sent to the client UI to be a part of a Redux app state. They are small enough to fit into memory and can be kept up to date in the browser.

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

Usage

To create a read model, pass the following arguments to the createReadModel factory function:

eventStore - a configured eventStore instance.
projection - functions converting an event stream into a read model storage. A projection form is dependent on the used adapter. When the default adapter is used, a projection is a map of functions (one function for each event type) which manipulate data in the provided MongoDB-like store.
adapter - a read model adapter instance. A memory adapter supporting the MongoDB-like query language is used by default.

To create a view model, pass the following arguments to the createViewModel factory function:

eventStore - a configured eventStore instance.
projection - a map of redux-like reducer functions (one function for each event type).

To create a query facade for a read/view model, pass the following arguments to the createFacade factory function:

model - a read/view model resource a factory function created.
gqlSchema - a read model data schema description in terms of the GraphQL schema language.
gqlResolvers - a map of resolvers for replying to a GraphQL query depending on the specified gqlSchema and read model storage data.
customResolvers - optional resolvers for specific read/view models.

A facade supports the following functions to send queries to a read/view model:

executeQueryGraphql - gets data from read/view models using a GraphQL request;
executeQueryCustom - executes a custom resolver function;
dispose - removes a facade and releases resources.

The executeQueryGraphql function receives the following arguments:

qraphQLQuery (required) - the GraphQL query to get data;
graphQLVariables - specify it if the graphQLQuery contains variables;
jwtToken - non-verified actual JWT token provided from client.

The executeQueryCustom function receives the following arguments:

name (required) - a custom resolver name to handle a request;
customParams - custom parameters passed to a resolver function;
jwtToken - non-verified actual JWT token provided from client.

A custom query can be helpful in the following cases:

if the selected read model storage provides a n API for retrieving data, like Elasticsearch or Searchify;
to pass the actual view model state as a client-side redux initial state;
to use the selected adapter's internal features which are not accessible via a regular graphql query.

Example

Implement a read model for building a News state with custom GraphQL resolvers and use the resolve-query library to get the first news page. It handles events an aggregate produces ( see the resolve-command documentation).

resolve-query

Usage

Example

news-read-model.js