Graphql创建两个查询之间的关系.初始化前无法访问错误 [英] Graphql create relations between two queries.Error cannot access before initialization

问题描述

我有此代码:

const ProductType = new GraphQLObjectType({
    name: 'Product',
    fields: {
        id: { type: GraphQLID },
        name: { type: GraphQLString },
        category: {
            type: CategoryType,
            resolve: async (parent) => {
                return await Category.findOne({_id: parent.category});
            }
        }
    }
});

const CategoryType = new GraphQLObjectType({
    name: 'Category',
    fields: {
        id: { type: GraphQLID },
        name: { type: GraphQLString },
        products: {
            type: ProductType,
            resolve: async (parent, args) => {
                return await Product.find({category: parent._id});
            }
        }
    }
});

const Query = new GraphQLObjectType({
    name: 'Query',
    fields: {
        Categories: {
            type: new GraphQLList(CategoryType),
            resolve: async () => {
                return await Category.find();
            }
        }
    }
});

当我尝试编译时，我得到ReferenceError:初始化之前无法访问'CategoryType'.我了解我首先应该声明，并且只有在使用之后才声明，但是我在YouTube的一堂课上看到了类似的代码，我认为它应该可以，但是不能.

When i try to compile i get ReferenceError: Cannot access 'CategoryType' before initialization. I understand that first of all I should declare and only after that use, but I saw a similar code in one lesson on YouTube, and I think that it should work, but it’s not.

推荐答案

字段可以采用函数而不是对象.这样，函数内部的代码将不会立即被评估:

fields can take a function instead of an object. This way the code inside the function won't be evaluated immediately:

fields: () => ({
  id: { type: GraphQLID },
  name: { type: GraphQLString },
  category: {
    type: CategoryType,
    resolve: (parent) => Category.findOne({_id: parent.category}),
  }
})

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