Node.js 两个Mongoose模型中的循环依赖

我有两个相互依赖的mongoose模式的循环依赖性问题。代码如下：

// user.model.js
var mongoose = require('mongoose');
var transactionSchema = mongoose.model('Transaction').schema;

var userSchema = mongoose.Schema ({
  name : String,
  wallet: Number,
  transactions: [ {type: mongoose.Schema.Types.ObjectId, ref: 'Transaction'} ]
});

var User = mongoose.model('User', userSchema);

// transaction.model.js
var mongoose = require('mongoose');
var userSchema = mongoose.model('User').schema;

var transactionSchema = mongoose.Schema ({
  sourceUser: {type: mongoose.Schema.Types.ObjectId, ref: 'User'},
  targetUser: {type: mongoose.Schema.Types.ObjectId, ref: 'User'},
  amount: Number,
  status: String
});

var Transaction = mongoose.model('Transaction', transactionSchema);

按如下方式加载：

// app.js
 var mongoose = require('mongoose');

require('./models/user.model');
require('./models/transaction.model');

问题很明显，但不清楚如何解决。

user.model.js transaction.model.js

---

为什么需要在事务文件中导入userSchema？它没有被使用。transactionSchema也是一样。它被用作源用户和目标用户引用，但实际上并非如此。你不需要它。ref:'User'并不意味着您应该更早定义用户集合。我知道，问题解决了。我认为模式对于参考是必要的，但我错了。非常感谢。

var mongoose = require('mongoose');

var userSchema = mongoose.Schema ({
  name : String,
  wallet: Number,
  transactions: [ {type: mongoose.Schema.Types.ObjectId, ref: 'Transaction'} ]
});

var User = mongoose.model('User', userSchema);

var mongoose = require('mongoose');

var transactionSchema = mongoose.Schema ({
  sourceUser: {type: mongoose.Schema.Types.ObjectId, ref: 'User'},
  targetUser: {type: mongoose.Schema.Types.ObjectId, ref: 'User'},
  amount: Number,
  status: String
});

var Transaction = mongoose.model('Transaction', transactionSchema);