@enigmatis/polaris-middlewares

polaris-middlewares

This package contains middlewares for polaris graphql server.
You can use these middlewares & extensions separately using your apollo server.

For example:

import { makeExecutableSchema, applyMiddleware, ApolloServer } from 'apollo-server';
import {
    DataVersionMiddleware,
    SoftDeleteMiddleware,
    RealitiesMiddleware,
    IrrelevantEntitiesMiddleware,
} from '@enigmatis/polaris-middlewares';
const schema = makeExecutableSchema({ typeDefs, resolvers });
const schemaWithMiddlewares = applyMiddleware(
    schema,
    DataVersionMiddleware.getMiddleware(),
    SoftDeleteMiddleware.getMiddleware(),
    RealitiesMiddleware.getMiddleware(),
    IrrelevantEntitiesMiddleware.getMiddleware(),
);
const apolloServer = new ApolloServer({
    schema: schemaWithMiddlewares,
    context: ctx => getPolarisContext(ctx),
});

Data Version Middleware

Data version is a sequence that indicates a version of an entity. If you want to use polling in order to receive query differences (Deltas), you can use the data version middleware.

This middleware filters array of entities: if the entity/entities have the field dataVersion set on them, the middleware return only entities that have a bigger dataVersion than the data version that is set on the context (context.requestHeaders.dataVersion). If no dataVersion is set on context, no filter will be applied. If a single entity is returned, the filter will be applied as well. If an array of entities with no data version field is returned, no filter will be applied.

For example:

const beforeMiddleware = [
    { title: 'x', dataVersion: 2 },
    { title: 'y', dataVersion: 5 },
];

const afterMiddleware = [{ title: 'x', dataVersion: 5 }]; // context.requestHeaders.dataVersion is set to 3

Soft Delete Middleware

It works similar to data version middleware, filtering out all entities which are soft deleted (has a property called deleted set to true).

For example:

const beforeMiddleware = [
    { title: 'x', deleted: true },
    { title: 'y', deleted: false },
];
const afterMiddleware = [{ title: 'y', deleted: false }];

Irrelevant entities

These are entities with greater data version than the data version that was provided in the request, but that do not pass the filter you provided. For example, if you ask for items with data version greater than 1, which start with the letter 'a', the response will contain (in it's extensions) a list of ids of irrelevant entities - items which were updated after this data version (their data version is greater), but that their letter does not start with the letter 'a' (so they do not fit to the filter).
If your context object contains an irrelevant entities object under property context.returnedExtensions.irrelevantEntities, it adds the value of this property to the extensions object in the graphql response.
This middleware relies on naming conventions, which means that in order to activate the logic of this middleware, you need to name your DB entities just like how they appear in the GraphQL schema!

for example, setting the context irrelevant entities:

context.returnedExtensions.irrelevantEntities = { books: [1, 2, 3] };

and the graphql response:

const response = {
    data: {...},
    errors:[],
    extensions: {
        books: [1, 2, 3]
    }
}