Flutter cloud firestore : query document->map->array

Question

My db design is above picture. I wanna create a query which returns user where tags are matched. But i didnt any solution to query.

This is my flutter code:

But it doesnt work. How can i query array of map of document?

Answer 1

The courses is an array and not a map so you cannot use the dot notation to query. If the courses is made a collection (or a sub-collection) on it's own then you would be able to query users easily:

users -> {userId}
(col)     (doc)

courses -> {courseId}
(col)        (doc)

You would have to include a field userId in each course document which would be used to identify which user owns that course.

await firestore.collection("courses").where("tags", arrayContainsAny: tagKeys)

This will return all courses where the tags array contains at least 1 item in the tagKeys list. If you need exact match i.e. all the tags in tagKeys must be present in Firestore document then you would have to restructure the database as mentioned in this answer.

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Fetching all matching documents might not be ideal since you just need user IDs that matches the tags. In that case you can store a field which contains tags from all the courses in a single array field in the user document.