Would you be kind to tell me is there any way to set limitation on array size while creating Mongoose schema. For example

 var peopleSchema = new Schema({
    name: {
        type: String,
        required: true,
        default: true
    },
   /* here I want to have limit: no more than 10 friends.
    Is it possible to define in schema?*/
    friends: [{
        type: Schema.Types.ObjectId,
        ref: 'peopleModel'
    }]
})

Solution 1

With a small tweak to your schema setup you can add a validate option:

var peopleSchema = new Schema({
  name: {
    type: String,
    required: true,
    default: true
  },
  friends: {
    type: [{
      type: Schema.Types.ObjectId,
      ref: 'peopleModel'
    }],
    validate: [arrayLimit, '{PATH} exceeds the limit of 10']
  }
});

function arrayLimit(val) {
  return val.length <= 10;
}

Solution 2

starting from mongo 3.6 you can add validation for a collection at server end, each document inserted/updated will be validated against the validator $jsonSchema, only the valid gets inserted, validation error will be for invalid documents

db.createCollection("people", {
   validator: {
      $jsonSchema: {
         bsonType: "object",
         required: [ "name" ],
         properties: {
            name: {
               bsonType: ["string"],
               description: "must be a string"
            },
            friends: {
               bsonType: ["array"],
               items : { bsonType: ["string"] },
               minItems: 0,
               maxItems: 10,
               description: "must be a array of string and max is 10"
            }
         }
      }
   }
});

collection

> db.people.find()

valid document

> db.people.insert({name: 'abc' , friends : ['1','2','3','4','5','6','7','8','9','10']})
WriteResult({ "nInserted" : 1 })

invalid document

> db.people.insert({name: 'def' , friends : ['1','2','3','4','5','6','7','8','9','10', '11']})
WriteResult({
    "nInserted" : 0,
    "writeError" : {
        "code" : 121,
        "errmsg" : "Document failed validation"
    }
})

find

> db.people.find()
{ "_id" : ObjectId("5a9779b60546616d5377ec1c"), "name" : "abc", "friends" : [ "1", "2", "3", "4", "5", "6", "7", "8", "9", "10" ] }
> 

Solution 3

You can use $slice modifier at the time you push new friend id into your array https://docs.mongodb.com/manual/reference/operator/update/slice/#up._S_slice

$push: {
  friends: {
   $each: [id],
   $slice: -10
  }
}

Solution 4

This is my schema and array limit on assignedToId via an external function.

const mongoose = require("mongoose");
    const Schema = mongoose.Schema;

const taskSchema = new Schema({
  parentTask: {
    trim: true,
    type: Schema.Types.ObjectId,
    ref: "task",
  },
  assignedToId: [{
    trim: true,
    type: Schema.Types.ObjectId,
    ref: "Employees",
  }],
  createdBy: {
    trim: true,
    type: Schema.Types.ObjectId,
    ref: "Employees",
    required: [true, "User ID is required"]
  },
  createdByName: {
    trim: true,
    type: String,
    required: [true, "Creater name is required"]
  },
},
  {
    timestamps: true
  });

// Validations for assignedTo employees' size
taskSchema.path('assignedToId').validate(function (value) {
  console.log(value.length)
  if (value.length > 10) {
    throw new Error("Assigned person's size can't be greater than 10!");
  }
});

const Tasks = mongoose.model("Tasks", taskSchema);

module.exports = Tasks;