Chapter 2 - Trying to use $addField to count the num of favorite moviesm

MongoDB University M121: The MongoDB Aggregation Framework
#1

I tried to use $addField where count the num of favorite movies

var favorites = [   "Sandra Bullock",   "Tom Hanks",   "Julia Roberts",   "Kevin Spacey",   "George Clooney"]

 db.movies.aggregate([{$project:{"num_fav":1,"_id":0,"title":1}},{$addFields:{"num_fav":{$setIntersection:["$favorites","$cast"]}},{$count:"$num_fav"}])

It does not reconize “favourites”
Later I got …

Chapter 2: Basic Aggregation - Utility Stages Lab: Using Cursor-like Stages
#2

After the stage

the only fields left are num_fav and title. The field cast does not exist anymore and the $setIntersection will not work.

The variable favorites is JS variable, it is not a field name. The syntax $favorites is for a field name.

#3

I tried to intersect the arrays .Afterwards, the new field is empty.

{$addFields:{"num_fav":{$setIntersection:[["Sandra Bullock","Tom Hanks","Julia Roberts","Kevin Spacey","George Clooney"],"$reparto"]}}}

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#4

What is reparto?

#5

Reparto envolves the field cast

#6

Rerun the aggregation without the $addFields to see if is computed correctly.

If it is then you may try to filter out num_fav:[] to see if some documents remains.

#7 
 db.movies.aggregate({$project:{"_id":0,"cast":1,"title":1,"reparto":"$cast"}})

I got that correctly

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#8

Yes, that’s correct.

Have you tried:

In the few documents we see in the screenshot, an empty intersection is normal.