Increase value of a field inside an array of element - mongodb

Question

I have documents that has the following structure in my collection:
{
"_id": "1234566780",
"arrayField": [
{
"id": "1",
"count": 3
},
{
"id": "2",
"count": 5
}
]
}
I want to have a method in my CollectionRepository that increments the value of the field count by giving to the method the collection id and the field id of the elements in the arrayField.
I have the feeling that it is not possible to do it with Spring Data autogenerated queries by method names.
So I'm trying to do it with the #Query annotation, but I have no idea on how to do it, since I need to select the collection based on _id, then select the field inside the array based on id, and then increase the count by one. Any hints?

Answer 1

Sorry for the delay, here is a solution to your problem.
You can update a specific element of an array using arrayFilter update option. The MongoDB update operation would look like:
db.collection.update(
{"_id":"1234566780"},
{$inc:{"arrayField.$[elem].count":1}},
{arrayFilters:[{"elem.id":"2"}]}
Admiting you are using MongoDB server and MongoDB java Driver version 3.6 or greater you could use:
public void updateCollection () {
MongoCollection<Document> collection = mongoTemplate.getDb().getCollection("collection");
Bson query = new Document("_id", "1234566780");
Bson update = Updates.inc("arrayField.$[elem].count",1);
UpdateOptions updateOptions = new UpdateOptions().arrayFilters(Arrays.asList( Filters.eq("elem.id","2")));
collection.updateOne(query, update, updateOptions);
}
Indeed Spring data method signature is not likely to generate this update. What I suggest you is to extend a CustomCollectionRepository interface with your CollectionRepository. You could define this update method signature in this interface and implement it in a CustomCollectionRepositoryImpl class. Please find the part of the documentation that mention this solution.