首先，我們定義三個Schema

drawApply = new Schema({
    salesId: { type: Schema.ObjectId, ref: 'sales' },
    money: Number,
    status: { type: Number, default: 0 },
    createTime: { type: Date, default: Date.now }
});

sales = new Schema({
    name: { type: String, required: true, unique: true },
    pwd: String,
    phone: String,
    merchant: { type: Schema.ObjectId, ref: 
 
'merchant' },
    status: { type: Number, default: 0 }
});

merchant = new Schema({
    name: String,
    sname: String,
    type: String
});

　　返回的結果中除了drawApply表的資料外，還會包含salesId中_id，name，phone，merchant四個屬性的值（注：需要檢視什麼屬性就在第二個引數中明示，若populate方法中只有salesId引數，則會將sales表中所有屬性返回）。但是merchant屬性的值是以ObjectId的形式顯示的，如果想知道對應的merchant其它屬性的值，則需要再次使用到巢狀的

drawApply.find().populate({
    path: 'salesId',
    select: '_id name phone merchant',
    model: 'sales',
    populate: {
        path: 'merchant',
        select: '_id sname',
        model: 'merchant'
    }).sort({createTime: -1}).exec(function(err, list) {
  // list of drawApplies with salesIds populated and merchant populated
 

});

　　如果drawApply表中還存在其它ObjectId型別的欄位，則可以在populate方法後面繼續跟其它的populate，使用方法相同，如：

drawApply.find().populate({
    path: 'salesId',
    select: '_id name phone merchant',
    model: 'sales',
    populate: {
        path: 'merchant',
        select: '_id sname',
        model: 'merchant'
    })
    .populate('approver', 'name')
    .populate('operator', 'name')
    .sort({createTime: -1}).exec(function(err, list) {
  // list of drawApplies with salesIds populated and merchant populated
});