Kysely•3mo ago

Return type when fields are conditional

Probably more of a TypeScript question than a Kysely question, but how would I type the output of a wrapper function that allows the conditional specification of fields. E.g.

export function selectActivitiesByActivityId(activityIds: number[], fields: Array<keyof ActivityHistoryTable> = []) {
  const db = createKysely();
  let query = db.selectFrom(ACTIVITIES_TABLE)
  if(fields.length){
    query = query.select(fields);
  } else {
    query = query.selectAll();
  }
  query = query.where('activity_id', 'in', activityIds);
  return query.execute();
}

export function selectActivitiesByActivityId(activityIds: number[], fields: Array<keyof ActivityHistoryTable> = []) {
  const db = createKysely();
  let query = db.selectFrom(ACTIVITIES_TABLE)
  if(fields.length){
    query = query.select(fields);
  } else {
    query = query.selectAll();
  }
  query = query.where('activity_id', 'in', activityIds);
  return query.execute();
}

The inferred type is {} and I'd like the return type to include the fields that were specified in the fields property?

Solution:

https://kysely.dev/docs/recipes/conditional-selects

Conditional selects | Kysely

Sometimes you may want to select some fields based on a runtime condition.

Jump to solution

3 Replies

Ross•3mo ago

With some help from ChatGPT 4o, I eventually got to this which works:

export function selectActivitiesByActivityId<T extends (keyof ActivityHistoryTable)[]>(
  activityIds: number[],
  fields?: T
): Promise<Array<Pick<ActivityHistoryTable, T[number]>>> {
  const db = createKysely();
  let query = db.selectFrom(ACTIVITIES_TABLE);

  if (fields && fields.length > 0) {
    query = query.select(fields);
  } else {
    query = query.selectAll();
  }
  query = query.where('activity_id', 'in', activityIds);
  return query.execute() as Promise<Array<Pick<ActivityHistoryTable, T[number]>>>;
}

export function selectActivitiesByActivityId<T extends (keyof ActivityHistoryTable)[]>(
  activityIds: number[],
  fields?: T
): Promise<Array<Pick<ActivityHistoryTable, T[number]>>> {
  const db = createKysely();
  let query = db.selectFrom(ACTIVITIES_TABLE);

  if (fields && fields.length > 0) {
    query = query.select(fields);
  } else {
    query = query.selectAll();
  }
  query = query.where('activity_id', 'in', activityIds);
  return query.execute() as Promise<Array<Pick<ActivityHistoryTable, T[number]>>>;
}

Solution

koskimas•3mo ago

https://kysely.dev/docs/recipes/conditional-selects

Conditional selects | Kysely

Sometimes you may want to select some fields based on a runtime condition.

Ross•3mo ago

Oh, nice. Thank you

Gaming

Programming

Return type when fields are conditional