Mongodb aggregate - using $addFields inside a nested array to get true/ false - mongodb

Question

I've been trying to get data back with an additional field inside a nested array using $addFields.
The data is:
{
"show_id": 1,
"ext1_id": 126790,
"ext2_id": 44275,
"show_title": "Some Big title name",
"poster_url": "https://cdn.something.com/media/cover/o65bBCMVI.jpg",
"description": "show description",
"year": 2021,
"episodes": [
{
"episode_title": "episode title 1",
"episode_number": "01",
"version": null,
"file_id": "BAACAgUAAx0EYN2eLQADKWGOO8WclqGSBG6Kdy0DkRTAbLgGAALMAgACvj7BVnkS-frrNBz8HgQ",
"unique_id": "AgADzAIAAr4-wVY",
"message_id": 41,
"added_by": "bot",
"watched_by": [919205468, 1778357657],
"timestamp": "2021-11-12T15:32:46.172302"
},
{
"episode_title": "Episode title 2",
"episode_number": "02",
"version": null,
"file_id": "BAACAgUAAx0EYN2eLQADKmGOO9QAAZCDz6lonoW1R5zPUM9sVAACOAQAApgFAVdhA3c9xoF0oB4E",
"unique_id": "AgADOAQAApgFAVc",
"message_id": 42,
"added_by": "bot",
"watched_by": [919205468],
"timestamp": "2021-11-12T15:33:01.053049"
},
{
"episode_title": "episode title 3",
"episode_number": "03",
"version": null,
"file_id": "BAACAgUAAx0EYN2eLQADK2GOO9zX4pgK7d1ERd5BeQkvvobSAAKaBAAC2tNJVwYVsJ_OGprTHgQ",
"unique_id": "AgADmgQAAtrTSVc",
"message_id": 43,
"added_by": "bot",
"watched_by": [919205468],
"timestamp": "2021-11-12T15:33:08.862887"
}
],
"alt_titles": ["alt title", "ALT TITLE", "Alt-Title"],
"is_airing": true,
"added_by": "bot",
"timestamp": "2021-11-12T15:32:45.298797"
}
So basically, what I was trying was to add a field user_watched inside the episodes list so that it'll just return True / False by checking if the user_id is present in the watched_by list which is again inside the episodes list.
I also didn't want the watched_by to be retured in the result.
I expected something like this:
{
"show_id": 1,
"ext1_id": 126790,
"ext2_id": 44275,
"show_title": "Some Big title name",
"poster_url": "https://cdn.something.com/media/cover/o65bBCMVI.jpg",
"description": "show description",
"year": 2021,
"episodes": [
{
"episode_title": "episode title 1",
"episode_number": "01",
"version": null,
"file_id": "BAACAgUAAx0EYN2eLQADKWGOO8WclqGSBG6Kdy0DkRTAbLgGAALMAgACvj7BVnkS-frrNBz8HgQ",
"unique_id": "AgADzAIAAr4-wVY",
"message_id": 41,
"added_by": "bot",
"user_watched": true,
"timestamp": "2021-11-12T15:32:46.172302"
},
{
"episode_title": "Episode title 2",
"episode_number": "02",
"version": null,
"file_id": "BAACAgUAAx0EYN2eLQADKmGOO9QAAZCDz6lonoW1R5zPUM9sVAACOAQAApgFAVdhA3c9xoF0oB4E",
"unique_id": "AgADOAQAApgFAVc",
"message_id": 42,
"added_by": "bot",
"user_watched": true,
"timestamp": "2021-11-12T15:33:01.053049"
},
{
"episode_title": "episode title 3",
"episode_number": "03",
"version": null,
"file_id": "BAACAgUAAx0EYN2eLQADK2GOO9zX4pgK7d1ERd5BeQkvvobSAAKaBAAC2tNJVwYVsJ_OGprTHgQ",
"unique_id": "AgADmgQAAtrTSVc",
"message_id": 43,
"added_by": "bot",
"user_watched": true,
"timestamp": "2021-11-12T15:33:08.862887"
}
],
"alt_titles": ["alt title", "ALT TITLE", "Alt-Title"],
"is_airing": true,
"added_by": "bot",
"timestamp": "2021-11-12T15:32:45.298797"
}
I tried this following code in pymongo:
db.data_col.aggregate([
{'$sort' : { 'timestamp' : -1 } },
{'$facet' : {
"metadata": [ { "$count": "total" } ],
"data": [
{'$addFields': {
'episodes.user_watched':
{'$cond': [
{
'$in': [
919209968,
"$episodes.watched_by"
]
},
True,
False
]
}
}},
{ "$skip": offset }, { "$limit": limit },
{ '$project' : {"episodes.watched_by":0} } ,
]
}}
])
but I got every user_watched fields False even if the user_id is present among the watched_by list.
and the returned data.

Answer 1

Query
map on episodes, check if the user(1778357657) in in the watched_by array and add the field true/false
removed the field watched_by
*your query looks different i guess you do more things, but this produces the expected output
*your code didn't work because "$episodes.watched_by", is an array that contains all the watched_by arrays, with $map each array is checked separately.
PlayMongo
aggregate(
[{"$set":
{"episodes":
{"$map":
{"input": "$episodes",
"in":
{"$mergeObjects":
["$$this",
{"user_watched":
{"$in": [1778357657, "$$this.watched_by"]}}]}}}}},
{"$set": {"episodes.watched_by": "$$REMOVE"}}])