Graphql 创建两个 queries.Error 之间的关系在初始化之前无法访问

Question

我有这个代码：

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();
            }
        }
    }
});

当我尝试编译时出现 ReferenceError: Cannot access 'CategoryType' before initialization。我知道首先我应该声明并且只有在使用之后，但是我在 YouTube 上的一个课程中看到了类似的代码，我认为它应该可以，但它不是。

Answer 1

fields 可以接受一个函数而不是一个对象。这样函数内的代码就不会被立即求值：

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

Graphql 创建两个 queries.Error 之间的关系在初始化之前无法访问

Graphql create relations between two queries.Error cannot access before initialization

mongoose

mongodb

express

graphql

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