schema_loader

Load data against tree-like schema

Why schema loader?

When exporting data to the user, apart from exporting entities directly, we need to compose different associated entities to form a compound before sending it out. Asynchorous loading those associations while composing them into a tree, is not only tedious, but error-prone. So we borrowed the idea from GraphQL, using a predefined schema to describe the whole process, and let the framework to finish the dirty work.

Define Schema

Schema is a tree composed by various Node. Each node, defined through a object in Definition, represents an object, an array of object or a property in the final Document.

We can define a schema using Schema.fromDefinition(definition) as following

constuserSchema=Schema.fromDefinition({firstName: field('first_name'),lastName: field('last_name'),gender: field(),name: {__resolver__: (parent,info)=>[parent.first_name,parent.last_name].join(' ')},avatar: {__resolver__: (parent,info)=>batch(loadImage,[parent.avatar_id],(images)=>images[parent.avatar_id])}}

or extend an existing schema

constuserSchemaWithFriends=Schema.extend(userSchema,{friends: Schema.extend(userSchema,{__resolver__: (parent,info)=>loadFriends(parent.user_id)})})

Resolve Schema to document

After defining a schema, we can resolve schema to document using resolve(schema, rootValue, ?options): Promise. the rootValue can be a object or an Promise resolves to a target object.

if we have a user defined as:

letuser={first_name: 'Jim',last_name: 'Green',gender: 'male',avatar: 1}

resolving the user against userSchema as resolve(userSchema, user).then((document) => console.log(document)), we will get:

{firstName: 'Jim',lastName: 'Green',name: 'Jim Green',gender: 'male',avatar: 'http://www.example.com/avatars/1.png'}