Mongo: how to sort by external weight

Question

Following this question , which @NeilLunn elegantly answered, here is my problem in more detail.

This is a collection of documents, some of which are user_id. User user_id represents the user who created the document:

{ "user_id" : 11, "content" : "black", "date": somedate }
{ "user_id" : 6, "content" : "blue", "date": somedate }
{ "user_id" : 3, "content" : "red", "date": somedate }
{ "user_id" : 4, "content" : "black", "date": somedate }
{ "user_id" : 4, "content" : "blue", "date": somedate }
{ "user_id" : 90, "content" : "red", "date": somedate }
{ "user_id" : 7, "content" : "orange", "date": somedate }
{ "content" : "orange", "date": somedate }
{ "content" : "red", "date": somedate }
...
{ "user_id" : 4, "content" : "orange", "date": somedate }
{ "user_id" : 1, "content" : "orange", "date": somedate }
{ "content" : "red", "date": somedate }
{ "user_id" : 90, "content" : "purple", "date": somedate }

The front end draws pages, so each page will have 10 elements, and I do it with a restriction and skip, and it works very well.

In case we have a registered user, I would like to display the user's current registered documents, which he may find more interesting first , based on the users with whom he interacted.

, , . , , , .

, : [4,7,90,1].

, , , , . , .

:

, user_id , user_id 4 , user_id 7 .. , . :

• user_d: 4
• user_d: 7
• user_d: 90
• user_d: 1

? ?

Answer 1

[4,7,90,1], , :

db.collection.aggregate([
   { "$project": {
       "user_id": 1,
       "content": 1,
       "date": 1,
       "weight": { "$or": [
           { "$eq": ["$user_id": 4] }, 
           { "$eq": ["$user_id": 7] }, 
           { "$eq": ["$user_id": 90] }, 
           { "$eq": ["$user_id": 1] }, 
       ]}
   }},
   { "$sort": { "weight": -1, "date": -1 } }
])

, , , $or, user_id , $eq 1 0 true false.

, , $or. , , $or.

, $cond , .

Ruby Brain:

userList = [4, 7, 90, 1];

orCond = [];

userList.each do |userId|
  orCond.push({ '$eq' => [ 'user_id', userId ] })
end

pipeline = [
    { '$project' => {
        'user_id' => 1,
        'content' => 1,
        'date' => 1,
        'weight' => { '$or' => orCond }
    }},
    { '$sort' => { 'weight' => -1, 'date' => -1 } }
]

, , $cond:

db.collection.aggregate([
   { "$project": {
       "user_id": 1,
       "content": 1,
       "date": 1,
       "weight": { "$cond": [
           { "$eq": ["$user_id": 4] },
           10,
           { "$cond": [ 
               { "$eq": ["$user_id": 7] },
               9,
               { "$cond": [
                   { "$eq": ["$user_id": 90] },
                   7,
                   { "$cond": [
                       { "$eq": ["$user_id": 1] },
                       8, 
                       0
                   ]}
               ]}
           ]}
       ]}
   }},
   { "$sort": { "weight": -1, "date": -1 } }
])

, , . .

. :

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