如何根据 MongoDB 中的另一个数组更新嵌入式文档中的字段

Question

I am trying to update an embedded document in MongoDB using mongoose in nodejs. The document is simplified and shown below (The names in friendList is assumed to be unique):

{
    "_id" : ObjectId("5eb0617f3aec924ff42249cd"),
    "friendList" : [ 
        {
            "name" : "Alex",
            "flag" : false,
        },
        {
            "name" : "Bob",
            "flag" : false,
        },
        {
            "name" : "Caleb",
            "flag" : true,
        },        
        {
            "name" : "Debbie",
            "flag" : false,
        }
    ]
}

I would like to update this collection by:

1. accepting a Patch API with a request body containing a subset of friendList and
2. update the nested field flag .

For example, if I were to do a patch call from postman with the request body:

{
    "friendList":[
        {
            "name":"Alex",
            "flag":true
        },
        {
            "name":"Caleb",
            "flag":false
        },
        {
            "name":"Debbie",
            "flag":false
        }
    ]
}

then I should expect my document in MongoDB to look like this:

{
    "_id" : ObjectId("5eb0617f3aec924ff42249cd"),
    "friendList":[
        {
            "name":"Alex",
            "flag":true
        },
        {
            "name":"Bob",
            "flag":false
        },
        {
            "name":"Caleb",
            "flag":false
        },
        {
            "name":"Debbie",
            "flag":false
        }
    ]
}

What I have tried on nodejs is updating the entire request body:

function updateUser(req){
    User.findOneAndUpdate({'_id':req.params._id},req.body,{new:true});
}

which replaces the entire friendList array:

{
    "_id" : ObjectId("5eb0617f3aec924ff42249cd"),
    "friendList":[
        {
            "name":"Alex",
            "flag":true
        },
        {
            "name":"Caleb",
            "flag":false
        },
        {
            "name":"Debbie",
            "flag":false
        }
    ]
}

I have also tried using array operators like $ :

function updateUser(req){
    User.findOneAndUpdate(
        {'_id':req.params._id},
        {$addToSet:{
            "friendList":{
                $each:req.body.friendList}
            }
        },
        {new:true}
    );
}

which gave me the output:

{
    "_id" : ObjectId("5eb0617f3aec924ff42249cd"),
    "friendList" : [ 
        {
            "name" : "Alex",
            "flag" : false,
        },
        {
            "name" : "Bob",
            "flag" : false,
        },
        {
            "name" : "Caleb",
            "flag" : true,
        },        
        {
            "name" : "Debbie",
            "flag" : false,
        },
        {
            "name" : "Alex",
            "flag" : true,
        },
        {
            "name" : "Caleb",
            "flag" : false,
        },
    ]
}

which $addToSet considers both name and flag when making a comparison to check if the values exist in the array. It might work if I am able to intercept at this comparison phase such that only the name field is checked.

I have been exploring concepts like $[<identifier>] and arrayFilter but can't seem to make it work.

Answer 1

Simple $addToSet does not work, because your array is not ["Alex","Caleb","Debbie"] . Your array is

[ 
  {name: "Alex", flag: true}, 
  {name: "Caleb", flag: false}, 
  {name: "Debbie", flag: false} 
]

Element {name:"Alex", flag: true} is different to element {name: "Alex", flag: false} , that's the reason why your approach failed. I think you have to use aggregation pipeline, eg this one:

db.collection.aggregate([
   { $addFields: { newFriends: friendList } },
   {
      $set: {
         friendList: {
            $map: {
               input: "$friendList",
               in: {
                  name: "$$this.name",
                  flag: {
                     $cond: [
                        { $eq: [{ $indexOfArray: ["$newFriends.name", "$$this.name"] }, - 1] },
                        "$$this.flag",
                        { $arrayElemAt: [ "$newFriends.flag", { $indexOfArray: ["$newFriends.name", "$$this.name"] } ] }
                     ]
                  }
               }
            }
         }
      }
   },
   { $unset: "newFriends" }
])

Or if you like to work with index variable:

db.collection.aggregate([
   { $addFields: { newFriends: friendList } },
   {
      $set: {
         friendList: {
            $map: {
               input: "$friendList",
               in: {
                  $let: {
                     vars: { idx: { $indexOfArray: ["$newFriends.name", "$$this.name"] } },
                     in: {
                        name: "$$this.name",
                        flag: {
                           $cond: [
                              { $eq: ["$$idx", - 1] },
                              "$$this.flag",
                              { $arrayElemAt: ["$newFriends.flag", "$$idx"] }
                           ]
                        }
                     }
                  }
               }
            }
         }
      }
   },
   { $unset: "newFriends" }
])

Note, this will update only existing names. New names are not added to the array, your question is not clear in this regard. If you like to add also new elements then insert

{
   $set: {
      friendList: { $setUnion: ["$friendList", "$newFriends"] }
   }
},

just before { $unset: "newFriends" }

The aggregation pipeline can be used in an update:

User.findOneAndUpdate(
    {'_id':req.params._id},
    [
      { $addFields: { newFriends: req.body.friendList } },
      {
         $set: { ...
      }
    ]
);