一对一

嵌套文档

{
  "_id": "user1",
  "name": "John Doe",
  "profile": {
    "id": "profile1",
    "brief": "This is John's profile"
  }
}

引用文档

// User 文档
{
  "_id": "user1",
  "name": "John Doe",
  "profileId": "profile1"
}

// Profile 文档
{
  "_id": "profile1",
  "brief": "This is John's profile"
}

const user = await UserModel.findById('user1').populate('profileId').exec()

一对多

嵌套文档

{
  "_id": "user1",
  "name": "John Doe",
  "posts": [
    { "id": "post1", "title": "Post 1" },
    { "id": "post2", "title": "Post 2" }
  ]
}

引用文档

// User 文档
{
  "_id": "user1",
  "name": "John Doe"
}

// Post 文档
{
  "_id": "post1",
  "title": "Post 1",
  "userId": "user1"
}
{
  "_id": "post2",
  "title": "Post 2",
  "userId": "user1"
}

const user = await UserModel.findById('user1').populate('profileId').exec()