Prisma graphql 计算域 [英] Prisma graphql computed fields

问题描述

我有这个数据模型:

type Item {
  id: ID! @unique
  title: String!
  description: String!
  user: User!
  pictures: [Picture]
  basePrice: Int!
  addons: [Addon]
}

我正在编写一个名为 parsedItem 的查询，它从参数中获取 id 并查找 Item(使用由 Prisma 生成的 Item 的默认查询)，如下所示:

I'm writing a query called parsedItem that takes the id from arguments and looks for the Item (using the default query for Item generated by Prisma), something like this:

 const where = { id: args.id };
 const item = await ctx.db.query.item({ where }, 
    `{
      id
      title
      ...

我需要在前端显示一个计算值:dynamicPrice"，它取决于项目拥有的插件数量.例如:Item #1 有 3 个插件，每个插件的价值为 5 美元.这个计算值应该是

I need to show on the frontend a computed value: "dynamicPrice" it depends on the quantity of the Addons that the Item has. e.g: Item #1 has 3 addons, each addons has a value of $5. This calculated value should be

dynamicPrice = basePrice + 3 * 5

插件关系可能会改变，所以我需要在前端发出的每个请求中计算这个.

The Addon relation could change, so I need to compute this in every request the frontend makes.

我非常想做这样的事情:

I'd like so much to do something like:

item.dynamicPrice = item.basePrice + (item.addons.length * 5)

并在解析器中返回这个项目，但这不起作用.抛出一个错误:

and return this item in the resolver, but this doesn't work. That throw an error:

"message": "无法在类型 \"Item\" 上查询字段 \"dynamicPrice\"."(当我尝试从前端查询项目时)

"message": "Cannot query field \"dynamicPrice\" on type \"Item\"." (when I try to query the Item from the frontend)

这个错误信息让我思考:我应该创建 dynamicPrice 作为数据模型上的一个字段吗?然后我可以在查询解析器中填充这个字段吗?我知道我可以，但这是一个好方法吗?

This error message makes me think: Should I create dynamicPrice as a field on the datamodel? Can I then populate this field in the query resolver? I know I can, but is this a good approach?

这是一个例子，我需要为这个 Item 模型创建更多的计算值.

This is an example, I need to create more computed values for this Item model.

对于这个简单的用例来说，最好的可扩展解决方案是什么?

推荐答案

您需要为 Item 类型的 dynamicPrice 字段创建字段解析器.它看起来像这样:

You need create field resolver for dynamicPrice field at Item type. It will looks like that:

const resolvers = {
  Query: {
    parsedItem: (parent, args, ctx, info) => {
      ...
    }
    ...
  },
  Item: {
    dynamicPrice: parent => parent.basePrice + parent.addons.length * 5
  }
}

您可以在指南中找到更多详细信息到常见的解析器模式.

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