If I have a simple collection such as:
Fruits:
Banana:
title: "Banana"
vitamins: ["potassium","B6","C"]
Apple:
title: "Apple"
vitamins: ["A","B6","C"]
And if I want to search fruits that contain vitamin B6, I would do the following:
db.collection("Fruits").whereField("vitamins", arrayContains: "A").getDocuments() { (querySnapshot, err) in
if let err = err {
print("Error getting documents: \(err)")
} else {
for document in querySnapshot!.documents {
print("\(document.documentID) => \(document.data())")
}
}
}
And that would show me all the Fruits in my collection that contain the vitamin A. However, how would I be able to search fruits that contain multiple vitamins, say vitamins B6 and C? I cannot simply search ["B6","C"] as it would then be looking for an array as opposed to independent strings.
Is this even possible in Cloud Firestore? If not is there any alternative way to do this?
It would be tempting to to look for documents that match multiple conditions, by chaining the conditions in the query:
db.collection("Fruits")
.whereField("vitamins", arrayContains: "B6")
.whereField("vitamins", arrayContains: "C")
But the documentation on compound queries suggests that you cannot currently have multiple arrayContains conditions in a single query.
So, it is not possible with what you have today. Consider instead using a map structure instead of an array:
Fruits:
Banana:
title: "Banana"
vitamins: {
"potassium": true,
"B6": true,
"C": true
}
Then you could query like this:
db.collection("Fruits")
.whereField("vitamins.B6", isEqualTo: true)
.whereField("vitamins.C", isEqualTo: true)
Firestore introduced the whereIn, arrayContains and arrayContainsAny methods in late 2019. These methods perform logical 'OR' queries, but have a limit of 10 clauses you can pass in (so max 10 vitamins you can search for).
Some solutions already mentioned restructuring your data. Another solution leveraging the restructuring approach is to not include the Vitamins into the Fruit document, but the other way around. This way you get all the documents 'Banana' is part of.
let vitaminsRef = db.collection('Vitamins').where('fruits', arrayContains: 'banana');
This solution allows you to circumvent the limit of 10 clauses. It gets all the 'Vitamin' documents that have 'Banana' in their 'Fruits' array in one read operation (think about pagination, if too many).
There's no way to do multiple array-contains queries in Firestore. You can, however, combine as many where conditions as practically possible. Therefore, consider this:
[Fruits]
<Banana>
title: "Banana"
vitamins:
potassium: true
b6: true
c: true
Firestore.firestore().collection("Fruits").whereField("vitamins.potassium", isEqualTo: true).whereField("vitamins.b6", isEqualTo: true)
However, this still doesn't allow a clean OR search. To query for fruits with vitamin-x or vitamin-y, you'd have to get more creative. Furthermore, this approach should not be used if there are a lot of possible values and they need to be combined with compound queries. That's because Firestore does not permit more than 200 composite indices and each composite index would need to specify the exact vitamin. Which means you'd have to create an individual composite index for vitamins.b6, vitamins.potassium, etc. and you only have 200 total.