typescript - 使用 Typescript、Babel 7、装饰器保留元数据

Question

我将 TypeORM 与 Babel 7 和 Typescript 一起使用，元数据似乎不存在于编译后的代码中。可以做些什么吗？还是这是使用 Babel 的限制？

错误

ColumnTypeUndefinedError: Column type for Photo#isPublished is not defined and cannot be guessed. Make sure you have turned on an "emitDecoratorMetadata": true option in tsconfig.json. Also make sure you have imported "reflect-metadata" on top of the main entry file in your application (before any entity imported).If you are using JavaScript instead of TypeScript you must explicitly provide a column type. at new ColumnTypeUndefinedError

Photo.js

import { Column, Entity, PrimaryGeneratedColumn } from 'typeorm'

@Entity()
export class Photo {

    @PrimaryGeneratedColumn()
    id: number


    @Column()
    isPublished: boolean
}

订单代码

import 'reflect-metadata'
import {createConnection} from 'typeorm'
import {Photo} from './entities/Photo'

createConnection({
    type: 'postgres',
    host: 'localhost',
    port: 5432,
    username: 'postgres',
    password: 'root',
    database: 'test',
    entities: [
        Photo
    ],
    synchronize: true,
    logging: false
}).then(connection => {
    // here you can start to work with your entities
}).catch(error => console.log(error))

package.json

{
    "name": "typescript-babel-node",
    "version": "0.1.0",
    "description": "",
    "main": "index.js",
    "scripts": {
        "dev": "run-p -r dev:run type-check:watch",
        "dev:run": "nodemon --exec babel-node --extensions '.ts,.js' src/index.js",
        "build": "babel src -d build --extensions '.ts,.js' src/index.js",
        "start": "node build/index.js",
        "type-check:watch": "tsc --watch",
        "test": "jest --watch"
    },
    "author": "",
    "license": "ISC",
    "dependencies": {
        "@types/node": "^10.12.0",
        "express": "^4.16.4",
        "pg": "^7.6.0",
        "ramda": "^0.25.0",
        "reflect-metadata": "^0.1.12",
        "typeorm": "^0.2.8"
    },
    "devDependencies": {
        "@babel/cli": "^7.1.2",
        "@babel/core": "^7.1.2",
        "@babel/node": "^7.0.0",
        "@babel/plugin-proposal-class-properties": "^7.1.0",
        "@babel/plugin-proposal-decorators": "^7.1.2",
        "@babel/plugin-proposal-object-rest-spread": "^7.0.0",
        "@babel/plugin-syntax-import-meta": "^7.0.0",
        "@babel/preset-env": "^7.1.0",
        "@babel/preset-typescript": "^7.1.0",
        "@types/express": "^4.16.0",
        "@types/jest": "^23.3.7",
        "@types/ramda": "^0.25.39",
        "babel-core": "^7.0.0-bridge.0",
        "babel-jest": "^23.6.0",
        "babel-plugin-module-resolver": "^3.1.1",
        "dot-env": "0.0.1",
        "eslint": "^5.7.0",
        "eslint-config-standard": "^12.0.0",
        "eslint-plugin-import": "^2.14.0",
        "eslint-plugin-node": "^7.0.1",
        "eslint-plugin-promise": "^4.0.1",
        "eslint-plugin-standard": "^4.0.0",
        "jest": "^23.6.0",
        "nodemon": "^1.18.5",
        "npm-run-all": "^4.1.3",
        "regenerator-runtime": "^0.12.1",
        "source-map-loader": "^0.2.4",
        "ts-jest": "^23.10.4",
        "typescript": "^3.1.3",
        "webpack": "^4.23.0",
        "webpack-cli": "^3.1.2"
    }
}

编辑:过了一会儿我找到了另一个 Babel 插件来解决这个问题，除了接受的答案中提到的那个: babel-plugin-transform-typescript-metadata似乎在使用 TypeORM 和 Nest。

Answer 1

开箱即用，如另一个答案中所述，这是不支持的。然而，我们可以编写一个 babel 插件来让它工作。

写代码不是很复杂，问题出在我们babel里面的信息有限。 Babel 不对 typescript 执行类型检查。这意味着我们没有任何语义信息，我们只有类型注释以及我们可以从中获得的信息。这意味着我们的解决方案必然非常有限

限制:

• 如果没有类型注释，我们就没有类型可写
• 如果我们有一个类型引用，我们只能使用类型名称，我们无法检查引用是否指向接口(interface)、类型别名、类或枚举。实际上，这意味着:
  • 如果类型是接口(interface)或类型别名，类型名称在运行时将是undefined，为了避免undefined，我们可以type ||如果类型没有关联的运行时值，对象默认为对象
  • 如果类型是枚举，Typescript 会根据枚举的类型在元数据中写入Number 或String。由于我们将类型名称写入元数据，这意味着您最终将在元数据中获得枚举的容器对象。

类型序列化可以从 typescript 编译器本身复制，只需很少的改动(它实际上只是两个函数 serializeTypeNode 和 serializeTypeList，大约 150 行代码)。

对于这个示例类，我们得到的结果是:

declare var decorator: any;

interface ISampleInterface {

}

enum Flags { One }
class OtherClass {}


type ArrayAlias = number[]

class Test {
    @decorator
    untypedProp; // no design:type
    @decorator
    nrProp: number // Number as expected
    @decorator
    strProp: string // String as expected
    @decorator
    boolProp: boolean // Boolean as expected

    @decorator
    nrPropUndefined: number | undefined // Number as expected
    @decorator
    strPropUndefined: string | undefined // String as expected
    @decorator
    boolPropUndefined: boolean | undefined // Boolean as expected

    @decorator
    arrayProp: number[]

    // Type references
    @decorator
    classRefProp: OtherClass; // OtherClass || Object  = Object since OtherClass is still a class at runtime

    @decorator
    interfaceRefProp: ISampleInterface;  // ISampleInterface || Object  = Object since ISampleInterface is undefined at runtime

    @decorator
    enumRefProp: Flags; // Flags || Object = Flags since Flags exists as a value at runtime, here TS would have written Number/String

    @decorator
    typeAliasProp: ArrayAlias; // ArrayAlias || Object = Object since ArrayAlias does not exist t runtime and in Babel swe have no idea ArrayAlias is actually an array

    @decorator
    selfClassRefProp: Test; // Test || Object  = Object since Babel puts decorators instantiation before class definition, this is a quirk, this may be fixable
}

实际的插件代码不是很大(减去从 TS 版本复制过来的方法):

export default declare((api: typeof import('@babel/core'), { jsxPragma = "React" }): PluginObj => {
  api.assertVersion(7);

  return {
    name: "transform-typescript-decorator-metadata",
    inherits: syntaxTypeScript,

    visitor: {
      ClassDeclaration(path) {
        var node = path.node;
        for (const field of node.body.body) {
          if (field.type !== "ClassProperty") continue;

          if (field.typeAnnotation && field.typeAnnotation.type === "TSTypeAnnotation" && field.decorators && field.decorators.length > 0) {
            const key = field.key as t.Identifier;
            const serializedType = serializeTypeNode(field.typeAnnotation.typeAnnotation);
            field.decorators.push(decorator(
              t.callExpression(
                t.memberExpression(t.identifier("Reflect"), t.identifier("metadata")), [
                  t.stringLiteral("design:type"),
                  t.logicalExpression("||", serializedType, createIdentifier("Object"))
                ])
            ))
          }
        }
      },
    }
  };
});

您可以找到完整的插件代码和工作示例 here

另一方面，插件顺序很重要，如果 @babel/plugin-proposal-class-properties 出现在我们的插件之前，它将删除所有属性，我们的插件将没有信息不再发射装饰器。这是我测试过的 .babelrc 并且它可以工作，我没有使用任何其他配置(但我不能说我已经尽力了)

  {
    "env": {},
    "ignore": [],
    "plugins": [
      "../plugin/plugin.js",
      ["@babel/plugin-proposal-decorators", { "legacy": true }],
      ["@babel/plugin-proposal-class-properties", { "loose": true }],
      "babel-plugin-transform-es2015-modules-commonjs"
    ],
    "presets": [
      "@babel/preset-typescript"
    ]
  }