Question

I Have a schema like so:

class Schemas

  constructor: ->
    @mongoose = require 'mongoose'
    @schema = @mongoose.Schema

    @EmployeeSchema = new @schema
      'firstname': { type: String, required: true }, 
      'lastname': { type: String, required: true }, 
      'email': { type: String, required: true, index: { unique: true }, validate: /\b[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,4}\b/ },
      'departmentId': { type: @schema.ObjectId, required: true }
      'enddate': String,
      'active': { type: Boolean, default: true } 

    @EmployeeSchemaModel = @mongoose.model 'employees', @EmployeeSchema

    @DepartmentSchema = new @schema
      'name': { type: String, required: true, index: { unique: true } }
      'employees' : [ @EmployeeSchema ]

    @DepartmentSchemaModel = @mongoose.model 'departments', @DepartmentSchema

So that my employees live in an array of employee documents inside a department

I have several department documents that have a number of employee documents stored in the employees array.

I then added a new department but it contained no employees. If I then attempt to add another department without employees, Mongoose produces a Duplicate key error for the employee.email field which is a required field. The employee.email field is required and unique, and it needs to be.

Is there anyway round this?

Answer 1

If you enable Mongoose debug logging with the coffeescript equivalent of mongoose.set('debug', true); you can see what’s going on:

DEBUG: Mongoose: employees.ensureIndex({ email: 1 }) { safe: true, background: true, unique: true }      
DEBUG: Mongoose: departments.ensureIndex({ name: 1 }) { safe: true, background: true, unique: true }      
DEBUG: Mongoose: departments.ensureIndex({ 'employees.email': 1 }) { safe: true, background: true, unique: true }  

By embedding the full EmployeeSchema in the employees array of DepartmentSchema (rather than just an ObjectId reference to it), you end up creating unique indexes on both employees.email and department.employees.email.

So when you create a new department without any employees you are ‘using up’ the undefined email case in the department.employees.email index as far a uniqueness. So when you try and do that a second time that unique value is already taken and you get the Duplicate key error.

The best fix for this is probably to change DepartmentSchema.employees to an array of ObjectId references to employees instead of full objects. Then the index stays in the employees collection where it belongs and you’re not duplicating data and creating opportunities for inconsistencies.