Mongoose model Schema with reference array: CastError: Cast to ObjectId failed for value "[object Object]"

Your article schema expects an array of ObjectId:

var ArticleSchema = new Schema({  ...  categories: [{     type: Schema.Types.ObjectId,     ref: 'Category' }]});

However req.body contains a category object:

categories:   [ { _id: '53c934bbf299ab241a6e0524',     name: '1111',     parent: '53c934b5f299ab241a6e0523',     __v: 0,     subs: [],     sort: 1 } ]

And Mongoose can't convert the category object to an ObjectId. This is why you get the error. Make sure categories in req.body only contains ids:

{ title: 'This is title',  content: '<p>content here</p>',  categories: [ '53c934bbf299ab241a6e0524' ],  updated: [ 1405697477413 ] }

Please use mongoose.Schema.Types.Mixed as data type of categories. I had the same issue with saving data array. It works for me.

var mongoose = require('mongoose'),    Schema = mongoose.Schema;var ArticleSchema = new Schema({    created: { type: Date, default: Date.now },    title: String,    content: String,    summary: String,    categories: [{type: Schema.Types.Mixed }]});mongoose.model('Article', ArticleSchema);