[英]How to refactor a “callback pyramid” into promise-based version
I'm currently struggeling to really understand how to refactor my code to use promises/the Q library. 我目前正在努力了解如何重构我的代码以使用promises / Q库。
Consider the following common basic example: I have a testcase that imports the same file twice into a mongodb and then checks whether the dataset name for the second import got some modifier at the end. 考虑以下常见的基本示例:我有一个测试用例,它将同一个文件两次导入mongodb,然后检查第二个导入的数据集名称是否在最后得到了一些修饰符。
importDataSet('myFile.csv',function () {
importDataSet('myFile.csv',function () {
DataSet.find({title: 1}, function (err, result) {
result.length.should.be.equal(2);
result[0].title.should.startWith('myFile');
result[1].title.should.startWith('myFile');
result[0].title.should.not.be.equal(result[0].title);
done();
});
});
});
done();
});
(done() is the final callback): (done()是最后的回调):
So how would I do this using promises? 那么我如何使用承诺来做到这一点? Preferably without changing the function signatures, (I followed the convention to have callbacks as the last parameter). 最好不要改变功能签名,(我遵循惯例将回调作为最后一个参数)。
I am not sure why done()
is called twice in your code, but without that, it may look similar to: 我不确定为什么在你的代码中调用done()
两次,但没有它,它可能看起来类似于:
importDataSet('myFile.csv')
.then(function () {
return importDataSet('myFile.csv')
}).then(function () {
return DataSet.find({title: 1})
}).then(function (result) {
result.length.should.be.equal(2);
result[0].title.should.startWith('myFile');
result[1].title.should.startWith('myFile');
result[0].title.should.not.be.equal(result[0].title);
done();
});
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