Node.js - mongoose promises - 循环

I am having a trouble with mongoose used with node.js. In my model I am having only group supervisor's ID, and in this route I want also to add supervisorName to variable (this name is stored in Group model). So, yeah, I've read some about promises, but still, I dont have any idea how to solve that. (Basically, I just want to loop through all groups, get their models from mongodb, and assign supervisor name to every group)

我遇到了与node.js一起使用的mongoose的问题。在我的模型中，我只有组主管的ID，并且在此路由中我还想将supervisorName添加到变量（此名称存储在组模型中）。所以，是的，我已经阅读了一些关于承诺的内容，但是，我仍然不知道如何解决这个问题。 （基本上，我只是想遍历所有组，从mongodb获取他们的模型，并为每个组分配主管名称）

router.get('/manage', function(req, res, next) {
Group.find({}, function(err, groups) {
    groups.forEach(function(group) {
        Group.findById(group.supervisor, function(err, supervisor) {
            group.supervisorName = supervisor.name;
            console.log(supervisor.name);
        });
    });
}).then(function() {
    res.render('groups/groups_manage', {groups : groups});
});
});

1 个解决方案

#1

You can map your groups array into array of promises and use Promise.all to resolve them all.

您可以将groups数组映射到promises数组，并使用Promise.all解决所有问题。

router.get('/manage', function(req, res, next) {
    Group.find({})
    .exec() // 1
    .then(groups => {
        return Promise.all(groups.map(group => { // 2, 3
            return Group.findById(group.supervisor)
            .exec()
            .then((supervisor) => { // 4
                group.supervisorName = supervisor.name;
                return group;
            });
        }));
    })
    .then(propGroups => {
        res.render('groups/groups_manage', {groups : popGroups});
    });
});

Explanations:

1. Mongoose Model methods supports both callbacks and promises interface. However to use the promise interface we need to use the exec method and remove the callbacks.
2. Mongoose Model方法支持回调和promises接口。但是要使用promise接口，我们需要使用exec方法并删除回调。
3. Promise.all takes an array of promises. It waits for all of them to resolve and any of them to reject (give error). Note: The promises are executed in parallel
4. Promise.all采取了一系列承诺。它等待所有人解决，其中任何一个拒绝（给出错误）。注意：承诺是并行执行的
5. We have an array of group objects, we map them into promises. Calling .findById and again using exec to get a promise from it. Note: Remember to return your promises
6. 我们有一组组对象，我们将它们映射到promises中。调用.findById并再次使用exec来获取它的承诺。注意：请记住退还您的承诺
7. We update the object, and return it as the final result of promise.
8. 我们更新对象，并将其作为promise的最终结果返回。