Myujth

consider I have the following collection,

[

 
 "user_id": 7,
 "action": 1
 ,
 
 "user_id": 8,
 "action": 1
 ,
 
 "user_id": 9,
 "action": 1
 ,
 
 "user_id": 7,
 "action": 2
 

]

I need to find all users who has for example action 1 but not action 2.
In mysql It's possible to just select user_id with two queries and subtract this results, or use where not exists subquery.

how can I handle this with mongodb?

so my expected result is :

[8,9]

You can use the aggregation pipeline to first group all actions into one array plus the associated user id into objects and the filter to have action 1, but not 2, then keep only the id:

db.collection.aggregate([
 // group user id and all actions together
 
 $group: 
 _id: "$user_id",
 actions: 
 $addToSet: "$action"
 
 
 ,
 // filter documents which have 1 as action but not 2
 
 $match: 
 $and: [
 
 "actions": 1
 ,
 
 "actions": 
 $not: 
 $eq: 2
 
 
 
 ]
 
 ,
 // only keep the id
 
 $group: 
 _id: "$_id"
 
 
])

This returns:

[
 
 "_id": 8
 ,
 
 "_id": 9
 
]

Here is a link to a playgorund: https://mongoplayground.net/p/So4HjEXx3sn

You should consider how you structure your documents. Your design looks a bit like a relational database. It is advisable to model your documents according to your read accesses (if possible). In this case you could an user_id and an actions field, which has already all action ids grouped together.

You can use $group and $push the actions for the distinct user_id. Finally use $match with actions $eq ual to 1 but not equal ($ne) to 2

db.collection.aggregate([
 "$group": 
 "_id": "$user_id",
 "actions": "$push": "$action" 
 ,
 "$match": "actions": "$eq": 1, "$ne": 2 ,
 { "$project": "_id": 1 
])