when should I use object id ? instead of using just String

 car:{type:mongoose.Schema.Types.ObjectID,ref:'cars'}
 user:{type:mongoose.Schema.Types.ObjectID,ref:'users'},

instead of just using

 type:String

? untill now it was always

type:string

CodePudding user response：

With mongoose schema definition you don't need to use 'mongoose.Schema.Types.ObjectID' you can simply pass :

{
  ...
  entity: {
     type: 'ObjectId',
     ref: 'entity'
  }
  ...
}

As defined here ObjectId is the default generated _id unique value of document storing timestamp and counter.

for a simple answer to 'when should I use object id ?' : when it refers to another document that use ObjectId

CodePudding user response：

1. You are defining a relation between specific collections. Basically be defining user:{type:mongoose.Schema.Types.ObjectID,ref:'users'}, in a schema, you are telling mongoose, that the user attribute is not just a plain string, but a reference to the _id of a document in users collection. You can then (e.g.) use functions like .populate('user') to perform a lookup on this previously defined relation.

2. You are restricting what can be stored in this attribute. If you define this attribute as a plain string, you can store everything you want in it without an error being raised, even if it is no valid _id of a foreign document. Defining it as an ObjectId helps to prevent errors, because only valid IDs can be stored in this attribute.