syncIndex failed creating index for the field with name 'key'

[1nstinct]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Mongoose version

8.7.0

Node.js version

18.18.0

MongoDB server version

6.0.19

Typescript version (if applicable)

No response

Description

Schema

const ObjectKeySchema = new mongoose.Schema({
  key: {
    type: String,
    required: true,
    unique: true,
  },
  type: {
    type: String,
    required: false,
  },
}, {
  timestamps: false,
  versionKey: false,
});

ObjectKeySchema.index({ key: 1 });

The index key_1 already exists in the DB, but the function call ObjectKey.syncIndexes() throws an error:

MongoServerError: An existing index has the same name as the requested index. When index names are not specified, they are auto generated and can cause conflicts. Please refer to our documentation. Requested index: { v: 2, key: { key: 1 }, name: "key_1", background: true }, existing index: { v: 2, unique: true, key: { key: 1 }, name: "key_1", background: true }
at Connection.sendCommand (/data/node_modules/mongodb/lib/cmap/connection.js:289:27)
at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
at async Connection.command (/data/node_modules/mongodb/lib/cmap/connection.js:312:26)
at async Server.command (/data/node_modules/mongodb/lib/sdam/server.js:167:29)
at async CreateIndexesOperation.executeCommand (/data/node_modules/mongodb/lib/operations/command.js:73:16)
at async CreateIndexesOperation.execute (/data/node_modules/mongodb/lib/operations/indexes.js:122:9)
at async tryOperation (/data/node_modules/mongodb/lib/operations/execute_operation.js:192:20)
at async executeOperation (/data/node_modules/mongodb/lib/operations/execute_operation.js:69:16)
at async Collection.createIndex (/data/node_modules/mongodb/lib/collection.js:326:25) {
  errorResponse: {
    ok: 0,
    errmsg: 'An existing index has the same name as the requested index. When index names are not specified, they are auto generated and can cause conflicts. Please refer to our documentation. Requested index: { v: 2, key: { key: 1 }, name: "key_1", background: true }, existing index: { v: 2, unique: true, key: { key: 1 }, name: "key_1", background: true }',
    code: 86,
    codeName: 'IndexKeySpecsConflict',
    '$clusterTime': {
      clusterTime: new Timestamp({ t: 1732303578, i: 14 }),
      signature: [Object]
    },
    operationTime: new Timestamp({ t: 1732303578, i: 14 })
  },
  ok: 0,
  code: 86,
  codeName: 'IndexKeySpecsConflict',
  '$clusterTime': {
    clusterTime: new Timestamp({ t: 1732303578, i: 14 }),
    signature: {
      hash: Binary.createFromBase64('OIA61Np4Zxmq4QBf1Ih5rquR7m0=', 0),
      keyId: new Long('7398342335731335169')
    }
  },
  operationTime: new Timestamp({ t: 1732303578, i: 14 }),
  [Symbol(errorLabels)]: Set(0) {}
}

Steps to Reproduce

1. Create schema
2. Run syncIndex()

Expected Behavior

Should ignore creating existing index.