uuid repeated many times

[frani]

v12.18.3

Describe the bug

I generate a UUID to set on every object that persist in a MongoDB, after two month of develop we realise that we have many UUID repeated:

• 7 % with => 26130a26-8a17-4338-8b07-54516d3dc1a8
• 5 % with => d56f1da2-f1f5-4ecc-96f2-ff2725c05c7f
• 5 % with => 7d28aa23-3b21-4ee1-a1cb-b34b0e7a7299
• 4 % with => d4440d2b-fc2a-4ccd-a9da-f8d3490a4b6b
• 3 % with => 3bd1baf0-168d-49d8-9c0f-62a4de1877f1
  ...
  and so on.

[Clear, concise description of the problem]

How to reproduce

and example of my model schema and how I am calling UUID:

const mongoose = require('mongoose')
const { v4: uuid } = require('uuid')

const model = new mongoose.Schema(
  {
    uuid: {
      type: String,
      default: uuid(),
      unique: true,
      required: true,
      index: true
    },
    ...
  },
  {
    collection: vars.mongo.collections.model,
  }
)

Expected behavior

generate different UUIDs every time that I created a new object to persist in my DB

Runtime

• OS: Linux
• Runtime: Node.js
• Runtime Version: v12.18.3

[broofa]

You're specifying a fixed uuid string for your uuid column's default value (uuid() is evaluated immediately, so whatever uuid that returns is your default value). Any/all models created w/out an explicit uuid property will all have that [duplicate] uuid. The reason you're getting duplicates on a variety of uuids is that the default uuid changes each time the process restarts.

I suspect what you want is to pass uuid as the default function by doing default: uuid, instead of default: uuid(),.

Side note: With both unique and index enabled I'm surprised Mongo didn't throw when you attempted to insert duplicates. (Not a Mongo user, but I assume unique indexes behave similarly to MySQL et al.)

Figuring out how to fix up that DB is gonna be a challenge...

[frani]

thanks for this nice explain,

your suspects were right!

and about mongoose, may be I was wrong of how I declared model

I found a note that recomend to declare index in the next way:

const mongoose = require('mongoose')
const { v4: uuidv4 } = require('uuid')

const model = new mongoose.Schema(
  {
    uuid: {
      type: String,
      default: uuidv4,
      required: true
    },
    ...
  },
  {
    collection: vars.mongo.collections.model,
  }
)

model.index(
  {
    uuid: 1
  },
  {
    unique: true
  }
)

thanks for fast responde, answer and the gif haha