Why does my mongodb query return 0 results? - mongodb

Question

This is my database collection:
With this go code, I try to get all the users who are either involved in the story or created the story with the given id.
func main() {
for stf.DB == nil {
}
collection := stf.DB.Collection("user")
ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
defer cancel()
id, _ := primitive.ObjectIDFromHex("5cb4dd7e29d3dca573a73d4c")
fter := bson.M{"_id": id}
involvedFilter := bson.M{"stories_involved": fter}
createdFilter := bson.M{"stories_created": fter}
filter := bson.M{"$or": []bson.M{involvedFilter, createdFilter}}
cur, err := collection.Find(ctx, filter)
if err != nil {
log.Fatal(err.Error())
}
defer cur.Close(ctx)
for cur.Next(ctx) {
var result bson.M
err := cur.Decode(&result)
if err != nil {
log.Fatal(err.Error())
}
fmt.Println(result)
}
if err := cur.Err(); err != nil {
log.Fatal(err.Error())
}
}
The code doesn't output any errors, but it also doesn't output any objects...
Thanks for your help in advance!

Answer 1

Your query translates into:
{"$or":[
{"stories_involved":{
"_id": ObjectId("5cb4dd7e29d3dca573a73d4c")}},
{"stories_created":{
"_id":ObjectId("5cb4dd7e29d3dca573a73d4c")}}
]}
Which means that it's searching for either a document with a nested document
i.e:
{stories_involved: {_id: <value>}} OR {stories_created: {_id: <value>}}.
However, the documents in the collection contains nested document array i.e:
{stories_involved: [{_id:<value>}]} OR {stories_created: [{_id:<value>}]}
This is the reason your query is not returning any value (and no error because the query syntax is correct).
There are two ways of Querying a document nested in an array using dot notation. If you know the index of the array for the document, you can just specify the position:
id, _ := primitive.ObjectIDFromHex("5cb4dd7e29d3dca573a73d4c")
involvedFilter := bson.M{"stories_involved.0._id": id}
createdFilter := bson.M{"stories_created.0._id": id}
filter := bson.M{"$or": []bson.M{involvedFilter, createdFilter}}
cur, err := collection.Find(ctx, filter)
If you do not know the index position of the document nested in the array, concatenate the name of the array field, with a dot (.) and the name of the field in the nested document:
id, _ := primitive.ObjectIDFromHex("5cb4dd7e29d3dca573a73d4c")
involvedFilter := bson.M{"stories_involved._id": id}
createdFilter := bson.M{"stories_created._id": id}
filter := bson.M{"$or": []bson.M{involvedFilter, createdFilter}}
cur, err := collection.Find(ctx, filter)
See also MongoDB: Query Documents