在 vanilla GraphQL 中实现分页

Question

到目前为止，我发现的每个教程都通过 Apollo、Relay 或其他一些魔术框架在 GraphQL 中实现了分页。我希望在这里找到类似问题的答案，但它们不存在。我了解如何设置查询，但我不清楚如何实现解析器。

有人能指出我正确的方向吗？如果有帮助，我正在使用 mongoose/MongoDB 和 ES5。

编辑：值得注意的是，如果您选择使用graphql.js，learning GraphQL 的官方网站没有分页条目。

编辑 2：我喜欢有 一些 人在进行研究之前投票结束问题，而其他人则利用他们的知识来帮助他人。无论你多么努力，你都无法阻止进步。 （：

Answer 1

普通 GraphQL 中的分页

// Pagination argument type to represent offset and limit arguments
const PaginationArgType = new GraphQLInputObjectType({
  name: 'PaginationArg',
  fields: {
    offset: {
      type: GraphQLInt,
      description: "Skip n rows."
    },
    first: {
      type: GraphQLInt,
      description: "First n rows after the offset."
    },
  }
})

// Function to generate paginated list type for a GraphQLObjectType (for representing paginated response)
// Accepts a GraphQLObjectType as an argument and gives a paginated list type to represent paginated response.
const PaginatedListType = (ItemType) => new GraphQLObjectType({
  name: 'Paginated' + ItemType, // So that a new type name is generated for each item type, when we want paginated types for different types (eg. for Person, Book, etc.). Otherwise, GraphQL would complain saying that duplicate type is created when there are multiple paginated types.
  fields: {
    count: { type: GraphQLInt },
    items: { type: new GraphQLList(ItemType) }
  }
})

// Type for representing a single item. eg. Person
const PersonType = new GraphQLObjectType({
  name: 'Person',
  fields: {
    id: { type: new GraphQLNonNull(GraphQLID) },
    name: { type: GraphQLString },
  }
})

// Query type which accepts pagination arguments with resolve function
const PersonQueryTypes = {
  people: {
    type: PaginatedListType(PersonType),
    args: { 
      pagination: { 
        type: PaginationArgType, 
        defaultValue: { offset: 0, first: 10 } 
      },
    },
    resolve: (_, args) => {
      const { offset, first } = args.pagination
      // Call MongoDB/Mongoose functions to fetch data and count from database here.
      return {
        items: People.find().skip(offset).limit(first).exec()
        count: People.count()
      }
    },
  }
}

// Root query type
const QueryType = new GraphQLObjectType({
  name: 'QueryType',
  fields: {
    ...PersonQueryTypes,
  },
});

// GraphQL Schema
const Schema = new GraphQLSchema({
  query: QueryType
});

查询时：

{
  people(pagination: {offset: 0, first: 10}) {
    items {
      id
      name
    }
    count
  }
}

已创建启动板here。

Answer 2

您可以通过多种方式实现分页，但这里有两个使用 Mongoose 的简单示例解析器来帮助您入门：

使用限制和跳过的简单分页：

(obj, { pageSize = 10, page = 0 }) => {
  return Foo.find()
    .skip(page*pageSize)
    .limit(pageSize)
    .exec()
}

使用 _id 作为光标：

(obj, { pageSize = 10, cursor }) => {
  const params = cursor ? {'_id': {'$gt': cursor}} : undefined
  return Foo.find(params).limit(pageSize).exec()
}