构造类型 | GraphQL 中文网

对于许多应用，你可以在应用启动时定义固定结构，并使用 GraphQL 结构语言来定义它。在某些情况下，以编程方式构建结构很有用。你可以使用 GraphQLSchema 构造函数来完成此操作。

¥For many apps, you can define a fixed schema when the application starts, and define it using GraphQL schema language. In some cases, it’s useful to construct a schema programmatically. You can do this using the GraphQLSchema constructor.

当你使用 GraphQLSchema 构造函数创建结构时，你可以将它们创建为单独的对象类型，而不是仅使用结构语言定义 Query 和 Mutation 类型。

¥When you are using the GraphQLSchema constructor to create a schema, instead of defining Query and Mutation types solely using schema language, you create them as separate object types.

例如，假设我们正在构建一个简单的 API，可让你根据 ID 获取一些硬编码用户的用户数据。使用 buildSchema 我们可以编写一个服务器：

¥For example, let’s say we are building a simple API that lets you fetch user data for a few hardcoded users based on an id. Using buildSchema we could write a server with:

import express from "express";
import { createHandler } from "graphql-http/lib/use/express";
import { buildSchema } from "graphql";
 
const schema = buildSchema(`
  type User {
    id: String
    name: String
  }
 
  type Query {
    user(id: String): User
  }
`);
 
// Maps id to User object
const fakeDatabase = {
  a: {
    id: "a",
    name: "alice",
  },
  b: {
    id: "b",
    name: "bob",
  },
};
 
const root = {
  user({ id }) {
    return fakeDatabase[id];
  },
};
 
const app = express();
app.all(
  "/graphql",
  createHandler({
    schema,
    rootValue: root,
  })
);
app.listen(4000);
console.log("Running a GraphQL API server at localhost:4000/graphql");

我们可以在不使用 GraphQL 结构语言的情况下实现相同的 API：

¥We can implement this same API without using GraphQL schema language:

import express from "express";
import { createHandler } from "graphql-http/lib/use/express";
import {
  GraphQLObjectType,
  GraphQLString,
  GraphQLSchema,
} from "graphql";
 
// Maps id to User object
const fakeDatabase = {
  a: {
    id: "a",
    name: "alice",
  },
  b: {
    id: "b",
    name: "bob",
  },
};
 
// Define the User type
const userType = new GraphQLObjectType({
  name: "User",
  fields: {
    id: { type: GraphQLString },
    name: { type: GraphQLString },
  },
});
 
// Define the Query type
const queryType = new GraphQLObjectType({
  name: "Query",
  fields: {
    user: {
      type: userType,
      // `args` describes the arguments that the `user` query accepts
      args: {
        id: { type: GraphQLString },
      },
      resolve: (_, { id }) => {
        return fakeDatabase[id];
      },
    },
  },
});
 
const schema = new GraphQLSchema({ query: queryType });
 
const app = express();
app.all(
  "/graphql",
  createHandler({
    schema,
  })
);
app.listen(4000);
console.log("Running a GraphQL API server at localhost:4000/graphql");

当我们使用这种创建 API 的方法时，根级别解析器是在 Query 和 Mutation 类型上实现的，而不是在 root 对象上实现的。

¥When we use this method of creating the API, the root level resolvers are implemented on the Query and Mutation types rather than on a root object.

如果你想从其他内容（例如数据库结构）自动创建 GraphQL 结构，这尤其有用。你可能具有用于创建和更新数据库记录之类的通用格式。这对于实现联合类型等不能完全映射到 ES6 类和结构语言的功能也很有用。

¥This is particularly useful if you want to create a GraphQL schema automatically from something else, like a database schema. You might have a common format for something like creating and updating database records. This is also useful for implementing features like union types which don’t map cleanly to ES6 classes and schema language.

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