Question

我正在努力了解如何在另一个承诺中解决承诺我想要实现的步骤如下：

通过User（功能）

UserManager

改变其firstName
通过User（正常运行）

UserManager

我希望测试UserManager.saveUser(user);对成功返回true的响应。但是我收到了一个错误。

UserManagerTest.js

//[...]

it("Should save a user to the database", function () {
    var response = UserManager.getUserByLogin("Foo.Bar@provider.com", "Test")
        .then(function (user) {
            user.firstName = "Macarena";
            return UserManager.saveUser(user);
        })
        .catch((error) => {
            console.log("This error occured: "+error);
            return false;
        })
    return Promise.all([
        expect(response).to.eventually.be.true
    ]);
});

//[...]

控制台输出

  1) UserManager Save Should save a user to the database:
     AssertionError: expected undefined to be true
      at node_modules/chai-as-promised/lib/chai-as-promised.js:305:22
      at process._tickCallback (internal/process/next_tick.js:109:7)

UserManager.js

static saveUser(user){
    return new Promise((resolve, reject) => {
        pool.getConnection((err, connection)=> {
            if(err) reject(err);

            connection.query("SHOW COLUMNS FROM User;", (error, results, fields) => {
                if(error) reject(error);

                var availableFields = {savable: [], primary: []};
                //[...]
                resolve(availableFields);
            });

            connection.release();
        });
    })
    .then((result) => {
        var usedFields = {savable: [], primary: []};
        //[...]
        return usedFields;
    })
    .then((result) => {
        var sqlParams = [];
        var sql = "UPDATE User SET";
        //[...]
        sql += ";";
        pool.getConnection((err, connection) => {
            if(err) throw err;

            connection.query(sql, sqlParams, (error, results, fields) => {
                if(error) throw error;
                connection.release();
                return results.affectedRows == 1;
            });
        });
    })
    .catch((error) => {
        console.log(error);
        throw error;
    })
};

Answer 1

第二个then((result)=> ...)不返回任何内容，因此undefined

return results.affectedRows == 1;位于lambda中。它返回那个lambda，而不是周围的`then``

您需要更改pool.getConnection的语义，将其从回调更改为Promise。将其包裹在Promise中，解决它并将其链接起来，看起来像

return new Promise((resolve, reject) => {

    pool.getConnection((err, connection) => {
        if(err) {
             //see @robertklep comment
             try { connection.release(); } catch(e) { /* ignore ? */ }
             return reject(err);
        }

        connection.query(sql, sqlParams, (error, results, fields) => {
            if(error) throw error;
            connection.release();
            resolve(results.affectedRows == 1);
        });
    });
})

Answer 2

MySql是异步的，不会返回承诺。

function queryDB(result) {
  return new Promise((resolve, reject) => {
        var sqlParams = [];
        var sql = "UPDATE User SET";
        //[...]
        sql += ";";
        pool.getConnection((err, connection) => {
            if(err) {
                reject(err);
                return connection.release();
            }

            connection.query(sql, sqlParams, (error, results, fields) => {
                if(error) ? reject(error) : resolve(results.affectedRows == 1);
                connection.release();
            });
        });
  })
}

测试另一个Promise的承诺.then（）

2 个答案: