我有我使用的简单代码如下：
// mongoose helper methods
const saveInstance = (name, schema, obj) => {
const Model = mongoose.model(name, schema);
const Instance = new Model(obj);
return Instance.save();
};
该架构没有 ID 属性，但我在数据库中看到了这个：
"_id": {
"$oid": "5c14201afbf31900047f9ccf"
},
我想假设 Mongoose 正在创建这个 ID，还是 MongoDB 创建了这个？你能提供一个参考吗？
另外，为什么对象中对象的语法很奇怪，为什么不直接将 ID 作为值_id呢？
实际上有2个问题，让我逐个回答。
Mongoose 正在创建此 ID，还是由 MongoDB 创建？
更准确的答案是MongoDB Node.js 驱动程序（不是 MongoDB 服务器）
Let's make a clear distinction about what we are referring to:
Mongoose = The Node.js library that wraps around the official MongoDB Node.js driver
MongoDB (driver) = The database client library that connects to a MongoDB Server
MongoDB Server = The database server that stores your data, available in 2 editions: Community & Enterprise
Please note from the reference
MongoDB driver automatically generates an ObjectId for the _id field
...
MongoDB clients should add an _id field with a unique ObjectId.
The _id field is generated at the client side, unlike some databases that have the functionality to generate the primary field at the database server.
What actually happens is that Mongoose calls the ObjectId function that is provided by the MongoDB native driver. This is done without the server, i.e. you can generate an ObjectId without a server connection. You can try the following code:
/* no any database connection logic */
const TestSchema = new mongoose.Schema() // blank schema, should contain only _id field
const Test = mongoose.model('Test', TestSchema)
const test = new Test()
console.log(test.toString()) // this will log an object with an _id field
Also, why the strange syntax of an object in an object, why not just put the ID directly as value of
_id?
This is just a string representation of the actual 96-bit data. It's an Extended JSON format that is used to represent MongoDB documents as human readable.