如何使用 apollo / graphql 实现节点查询解析器

Question

我正在为 graphql 实现一个 node interface -- 一个非常标准的设计模式。

寻找有关为 graphql 实施节点查询解析器的最佳方法的指导

node(id ID!): Node

我遇到的主要问题是如何 encode/decode 类型名称的 ID，以便我们可以找到正确的 table/collection 进行查询。

目前我正在使用带有 pgcrytpo 的 postgreSQL uuid 策略来生成 id。

执行此操作的应用程序中的正确接缝在哪里？：

可以在数据库的主键生成中完成
可以在 graphql 接缝处完成 (using a visitor pattern maybe)

选择最佳接缝后：

how/where你encode/decode吗?

注意我的堆栈是：

ApolloClient/Server（来自 graphql-yoga）
节点
类型ORM
PostgreSQL

Answer 1

@Jonathan 我可以分享我的一个实现，你看看你的想法。这是在客户端上使用 graphql-js、MongoDB 和 relay。

/**
 * Given a function to map from an ID to an underlying object, and a function
 * to map from an underlying object to the concrete GraphQLObjectType it
 * corresponds to, constructs a `Node` interface that objects can implement,
 * and a field config for a `node` root field.
 *
 * If the typeResolver is omitted, object resolution on the interface will be
 * handled with the `isTypeOf` method on object types, as with any GraphQL
 * interface without a provided `resolveType` method.
 */
export function nodeDefinitions<TContext>(
  idFetcher: (id: string, context: TContext, info: GraphQLResolveInfo) => any,
  typeResolver?: ?GraphQLTypeResolver<*, TContext>,
): GraphQLNodeDefinitions<TContext> {
  const nodeInterface = new GraphQLInterfaceType({
    name: 'Node',
    description: 'An object with an ID',
    fields: () => ({
      id: {
        type: new GraphQLNonNull(GraphQLID),
        description: 'The id of the object.',
      },
    }),
    resolveType: typeResolver,
  });

  const nodeField = {
    name: 'node',
    description: 'Fetches an object given its ID',
    type: nodeInterface,
    args: {
      id: {
        type: GraphQLID,
        description: 'The ID of an object',
      },
    },
    resolve: (obj, { id }, context, info) => (id ? idFetcher(id, context, info) : null),
  };

  const nodesField = {
    name: 'nodes',
    description: 'Fetches objects given their IDs',
    type: new GraphQLNonNull(new GraphQLList(nodeInterface)),
    args: {
      ids: {
        type: new GraphQLNonNull(new GraphQLList(new GraphQLNonNull(GraphQLID))),
        description: 'The IDs of objects',
      },
    },
    resolve: (obj, { ids }, context, info) => Promise.all(ids.map(id => Promise.resolve(idFetcher(id, context, info)))),
  };

  return { nodeInterface, nodeField, nodesField };
}

然后：

import { nodeDefinitions } from './node';

const { nodeField, nodesField, nodeInterface } = nodeDefinitions(
  // A method that maps from a global id to an object
  async (globalId, context) => {
    const { id, type } = fromGlobalId(globalId);

    if (type === 'User') {
      return UserLoader.load(context, id);
    }

    ....
    ...
    ...
    // it should not get here
    return null;
  },
  // A method that maps from an object to a type
  obj => {

    if (obj instanceof User) {
      return UserType;
    }

    ....
    ....

    // it should not get here
    return null;
  },
);

load 方法解析实际对象。这部分你会更具体地与你的数据库等一起工作...... 不清楚的可以追问！希望对您有所帮助:)

Answer 2

暴露给客户端的id（全局对象id）不会持久保存在后端——编码和解码应该由GraphQL服务器自己完成。这是一个基于中继如何实现的粗略示例：

import Foo from '../../models/Foo'

function encode (id, __typename) {
  return Buffer.from(`${id}:${__typename}`, 'utf8').toString('base64');
}

function decode (objectId) {
  const decoded = Buffer.from(objectId, 'base64').toString('utf8')
  const parts = decoded.split(':')
  return {
    id: parts[0],
    __typename: parts[1],
  }
}

const typeDefs = `
  type Query {
    node(id: ID!): Node
  }
  type Foo implements Node {
    id: ID!
    foo: String
  }
  interface Node {
    id: ID!
  }
`;

// Just in case model name and typename do not always match
const modelsByTypename = {
  Foo,
}

const resolvers = {
  Query: {
    node: async (root, args, context) => {
      const { __typename, id } = decode(args.id)
      const Model = modelsByTypename[__typename]
      const node = await Model.getById(id)
      return {
        ...node,
        __typename,
      };
    },
  },
  Foo: {
    id: (obj) => encode(obj.id, 'Foo')
  }
};

注意：通过返回 __typename，我们让 GraphQL 的默认 resolveType 行为确定接口返回的类型，因此无需为 [=15= 提供解析器].

编辑：将 id 逻辑应用于多种类型：

function addIDResolvers (resolvers, types) {
  for (const type of types) {
    if (!resolvers[type]) {
      resolvers[type] = {}
    }
    resolvers[type].id = encode(obj.id, type)
  }
}

addIDResolvers(resolvers, ['Foo', 'Bar', 'Qux'])

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