Mongoose 预保存钩子正在触发，但不保存附加字段（不使用 model.update）

我正在尝试在我的架构中实现一个计数器来获取下一个问题编号。我已将其实现为 Mongoose 中的钩子预保存钩子，一切看起来都很好......除了实际的“数字”字段没有更新。我可以很容易地通过控制台记录的内容判断钩子正在触发，甚至该字段似乎已被分配。但可惜的是，无论我如何尝试，“数字”字段都不会出现在结果中。

我看到了一些与 Mongoose hooks 相关的问题，但它们似乎都与 findOneAndUpdate 等相关，而我没有使用这些问题。

这是我的完整模型，底部有挂钩：

var mongoose = require('mongoose');
var Schema = mongoose.Schema;
var Project = require('./projects.js');

var IssueSchema = new Schema({
    title: {type: String, required: true, trim: true,  index: true},
    number: {type: Number},
    description: {type: String, required: true},
    vote_up: {type: Number, default: 0},
    vote_down: {type: Number, default: 0},
    comments: [new Schema({
      _id: {type: Schema.ObjectId, ref: 'users'},
      description : {type: String},
      likes: {type: Number},
      date: {type: Date}
    })],
    attachments: [],
    fields: [new Schema({
      _id: {type: Schema.ObjectId, ref: 'fields'},
      value : {type: String}
    })],
    project: {type: Schema.ObjectId, required: true, index: true, ref: 'projects'},
    tags: {type: [Schema.ObjectId], required: false, default: ['56a2a0b1ea805d403f6d014b']},
    isResolved: {type: Boolean, default: false},
    created_by: {type: Schema.ObjectId, required: true, ref: 'users'},
    updated_by: {type: Schema.ObjectId, required: false, ref: 'users'},
    created_at: {type: Date, default: Date.now},
    updated_at: {type: Date, default: Date.now}
});

IssueSchema.pre('save', function(next){
    var now = new Date();
    this.updated_at = now;
    if(!this.created_at) {
        this.created_at = now;
    }
    next();
})
.pre('save', function(next) {
  Project.findOne({_id: this.project}).select('numberSeq').exec(function(err, doc) {
    if (err) {
      console.log(err);
    }
    console.log('pre-save hook firing');
      this.number = doc.numberSeq;
      console.log(this.number);
      next();
    });
})
.post('save', function(doc) {
  Project.update({_id: doc.project}, {$inc:  {numberSeq: 1}}, function(err, result) {
    if (err) {
      console.log(err);
    }
    console.log('Updated next number in seq for '  + doc.project);
  });
});

module.exports = mongoose.model('issues', IssueSchema);

以及插入问题的路线（我猜这不是问题所在）

app.post('/api/issue/create', function(req, res) {

    var issue = new Issues({
      title: req.body.title,
      description: req.body.description,
      fields: req.body.fields,
      attachments: req.body.attachments,
      project: req.body.project,
      created_by: req.user || req.body.created_by,
    });

    issue.save(function(err, result) {
      if (err) {
        return res.status(409).send({message: 'There was an error creating the issue: ' + err});
      }
      if (!result.number) {
        console.log('number = :(');
      }
      console.log(result);
      res.send({message: 'New issue created', result: result});
    });
  });

你错过了this这里的上下文，

.pre('save', function(next) {
  Project.findOne({_id: this.project}).select('numberSeq').exec(function(err, doc) {
    if (err) {
      console.log(err);
    }
    console.log('pre-save hook firing');
      this.number = doc.numberSeq;
      console.log(this.number);
      next();
    });
})

你说的地方：

this.number = doc.numberSeq;
console.log(this.number);

实际上指的是 findOne 查询的回调函数，因此您最终会得到正确的 console.log 和插入的错误数据。

您可以记住预保存挂钩的上下文，然后在回调中使用该上下文更新数字。像下面这样：

.pre('save', function(next) {
  var tat=this;
  Project.findOne({_id: this.project}).select('numberSeq').exec(function(err, doc) {
    if (err) {
      console.log(err);
    }
    console.log('pre-save hook firing');
      tat.number = doc.numberSeq;
      console.log(tat.number);
      next();
    });
})