javascript-无法读取未定义mysql的属性’typeCast’

我有代码：

import { createConnection } from 'mysql';
import { promisify } from 'util';

export default class Database {
    static instance: Database;

    query;
    db;

    constructor(user, password, database, host) {
        Database.instance = this;

        this.db = createConnection({ user, password, database, host });
        this.db.connect();
        this.query = promisify(this.db.query);
    }

    async getUser(id: number, filter: string = null) {
        return this.query('SELECT * FROM users WHERE id = ' + id)
        .then((err, res, fields) => {
            return res[0];
        });
    }
}

以及将ID传递给getUser的快速路由.

执行此代码后,我得到了这个堆栈.

(node:16544) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
(node:16544) UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'typeCast' of undefined
    at Database.query (<project>\node_modules\mysql\lib\Connection.js:199:34)
    at Database.query (internal/util.js:232:30)
    at Database.getUser (<project>\lib\structures\Database.js:13:21)
    at get (<project>\lib\api\routes\user.js:5:33)
    at Layer.handle [as handle_request] (<project>\node_modules\express\lib\router\layer.js:95:5)
    at next (<project>\node_modules\express\lib\router\route.js:137:13)
    at Route.dispatch (<project>\node_modules\express\lib\router\route.js:112:3)
    at Layer.handle [as handle_request] (<project>\node_modules\express\lib\router\layer.js:95:5)
    at <project>\node_modules\express\lib\router\index.js:281:22
    at param (<project>\node_modules\express\lib\router\index.js:354:14)
(node:16544) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 6)

我该如何解决？

解决方法:

Promisify(…)返回一个承诺.因此,您应该像这样使用await：await Promisify(…)

解决方案是：

1)删除this.query = promisify(…)和this.db.connect();构造函数中的代码行

2)您的数据库类和getUser函数应如下所示：

   export default class Database {
        static instance: Database;

        static async getInstance(user?, password?, database?, host?) {
            // all arguments above are optional

            if(!Database.instance){
                    const connection = createConnection({ user, password, database, host });
                    await connection.connect();
                const dbQuery = await promisify(this.promisify(connection.query));
                Database.instance = {
                    query: dbQuery 
                }
                return Database.instance;
            }
            return Database.instance;
        }

        static getUser(id: number, filter: string = null) {
            return Database.instance.query('SELECT * FROM users WHERE id = ' + id)
            .then((err, res, fields) => {
                return res[0];
            });
        }
    }

使用方法：

然后,在任何需要的地方：

async getUser(){
    let database = await Database.getInstance(); // or Database.getInstance(user, password ...)  to first initialize and then get the instance.

    return database.getUser(1234, filter);
}

标签：typescript,promise,es6-promise,javascript,mysql
来源： https://codeday.me/bug/20191110/2013324.html