我的节点项目当前包含嵌套回调的侧向圣诞树,以便获取数据并按正确的顺序处理它们。现在我正在尝试使用 Promises 重构它,但我不确定如何正确执行。
假设我要获取办公室列表,然后获取每个办公室的所有员工,然后获取每个员工的工资。最后,所有实体(办公室、员工和工资)都应该链接在一起并存储在数据库中。
一些伪代码说明了我当前的代码(省略了错误处理):
fetch(officesEndpoint, function (data, response) {
parse(data, function (err, offices) {
offices.forEach(function (office) {
save(office);
fetch(employeesEndPoint, function (data, response) {
parse(data, function (err, employees) {
// link each employee to office
save(office);
save(employee);
employees.forEach(function () {
fetch(salaryEndpoint, function (data, response) {
parse(data, function (err, salaries) {
// link salary to employee
save(employee);
});
});
});
});
});
});
});
});
我尝试用承诺来解决这个问题,但有几个问题:
- 有点冗长?
- 每个办公室都需要与其各自的员工联系起来,但在
saveEmployees
功能我只能访问员工,而不能访问链中更上层的办公室:
var restClient = require('node-rest-client');
var client = new restClient.Client();
var xml2js = require('xml2js');
// some imaginary endpoints
var officesEndpoint = 'http://api/offices';
var employeesEndpoint = 'http://api/offices/employees';
var salaryEndpoint = 'http://api/employees/:id/salary';
function fetch (url) {
return new Promise(function (resolve, reject) {
client.get(url, function (data, response) {
if (response.statusCode !== 200) {
reject(statusCode);
}
resolve(data);
});
});
}
function parse (data) {
return new Promise(function (resolve, reject) {
xml2js.parseString(data, function (err, result) {
if (err) {
reject(err);
}
resolve(result);
});
});
}
function saveOffices (offices) {
var saveOffice = function (office) {
return new Promise(function (resolve, reject) {
setTimeout(function () { // simulating async save()
console.log('saved office in mongodb');
resolve(office);
}, 500);
})
}
return Promise.all(offices.map(saveOffice));
}
function saveEmployees (employees) {
var saveEmployee = function (employee) {
return new Promise(function (resolve, reject) {
setTimeout(function () { // simulating async save()
console.log('saved employee in mongodb');
resolve(office);
}, 500);
})
}
return Promise.all(offices.map(saveEmployee));
}
fetch(officesEndpoint)
.then(parse)
.then(saveOffices)
.then(function (savedOffices) {
console.log('all offices saved!', savedOffices);
return savedOffices;
})
.then(function (savedOffices) {
fetch(employeesEndPoint)
.then(parse)
.then(saveEmployees)
.then(function (savedEmployees) {
// repeat the chain for fetching salaries?
})
})
.catch(function (error) {
console.log('something went wrong:', error);
});