fix(mongodb): fix #3834

[sibelius]

command started event example:

{
  event: CommandStartedEvent {
    name: 'commandStarted',
    address: '172.20.0.2:27017',
    connectionId: 12,
    serviceId: undefined,
    requestId: 686,
    databaseName: 'mydatabase',
    commandName: 'getMore',
    command: {
      getMore: new Long('1769182660590360229'),
      collection: 'Interaction',
      batchSize: 1000,
      lsid: [Object],
      '$clusterTime': [Object],
      '$db': 'mydatabase'
    }
  },
  commandName: 'getMore',
  collection: new Long('1769182660590360229')
}

Checklist

• Implement code
• Add tests
• Update TypeScript typings
• Update documentation
• Add CHANGELOG.asciidoc entry
• Commit message follows commit guidelines

[david-luna]

@sibelius thanks for your contribution into elastic-apm-node :)

What you propose enforces the specs related to mongodb instrumentation (link) for that specific command so indeed we should find a way to add the collection.

In order to move forward we need to complete the following tasks:

• be defensive on how we extract the collection name. The mongodb specs refers to command as a BSON's Document which does not specify the properties this PR inspects to get the collection name. Since the agent supports the range >=3.3.0 <7 we can assume that these properties may change across versions so an if (event.commandName === 'getMore' && event.command.collection) would fallback to old implentation if the collection property does not exist or contains an empty name.
• add a test to assert the change does what is supposed to do. Would come handy if there are changes in newer versions of mongodb that could break our logic to extract the name from getMore internal command. With the CI that test we can catch if this situation happens.
• make sure your code follow the linting rules. You can use npm run lint:fix to fix any auto-fixable issue.

[david-luna]

@sibelius

I've created #3919 to tackle the issue. Feel free to add any feedback there.

[sibelius]

It looks correct for me, tks