Properly Typing Mongoose Functions to Retain Document Methods

[felixwoestmann]

I'm trying to encapsulate Mongoose database operations in reusable functions, but I'm struggling with the TypeScript return type. When I extract database queries into helper functions, I lose access to document methods like .save().

// Current working code that I want to encapsulate in a function
const collectionJob = await this.databaseModels.collectionJob
  .findOne({
    _id: collectionJobId.jobId,
    user: collectionJobId.userId,
  })
  .populate<{ jobArguments: CollectionJobArgument }>("jobArguments");

if (collectionJob == null) {
  this.logger.error(
    `A severe error occurred. The CollectionJob with received ${JSON.stringify(collectionJobId.jobId)} was not found.`,
  );
  return;
}
collectionJob.status = "failed";
collectionJob.finishedAt = new Date();
await collectionJob.save(); // Works fine here

When I try to move this query into a function like:

async function getCollectionJob(jobId, userId): Promise<???> {  // What type should this be?
  // Query logic
  return collectionJob;
}

[vkarpov15]

Why do you need to set an explicit return type? The explicit type of collectionJob can be a bit tricky depending on how you defined your schemas and models, but TypeScript should be smart enough to infer it if you omit the function return type.