firestore query to get "next lesson" from list of lessons in a program

I have a firestore db that has a list of "programs" that a user can sign up for. Each program has a list of sessions/lessons that can be completed. The user can have more than one program set as "active", meaning they are working on it.

I am trying to build a query that will get the "next" lesson for each active program the user has enrolled in.

Each session/lesson has a separate detail and preview document as a sub collection of the program document. so I am looking to get a list of the "next session" previews based on ordering by week and day number. I also have a top level collection called userProgramProgress that has the following fields:

export interface UserProgramProgress {
docId: string,
userId: string,
programId: string,
isActive: boolean,
isComplete: boolean,
startDate: Date,
endDate: Date,
completedSessions: string[],
};


completedSessions is an array of the documentId's of the sessions that have been completed.

So I get the UserProgramProgress documents like this:


private userProgramProgressCollection = collection(
this.firestore,
'userProgramProgress'
);

const activeProgramsQuery = query(
this.userProgramProgressCollection,
where('userId', '==', uid),
where('isActive', '==', true)
);


Then I need to get the next session for each program and combine them into one list to return to the user.

something like this:

const cd = collectionData(activeProgramsQuery, {
idField: 'docId',
}).pipe(
switchMap((programs) =>
programs.map((p) => p as UserProgramProgress)
),
switchMap((program) => {
// use program completted sessions to get next sessions
const sessionCount = program.completedSessions.length ?? 0;

const programPreviewCollection = collection(
this.firestore,
'/trainingPrograms/' + program.programId + '/programSessionPreview'
);

const recordsQuery = query(
programPreviewCollection,
where('programId', '==', program.programId),
orderBy('programWeek', 'asc'),
orderBy('programDay', 'asc'),
limit(sessionCount + 1)
);

return collectionData(recordsQuery, {
idField: 'docId',
});
})
);


I am new to no-sql databse and need to know if I am on the right track. I plan to use the results here to loop through and get the records but this will result in a lot of reads.

for context this is inside an angular 18 app

QUESTION:


IS this the right direction for handling this scenario or should I do it a different way?

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