Syntax error MongoDB query to fetch only the “Name” field based on roles?

MongoDB query to fetch only the “Name” field based on roles?

For this, use aggregate(). Here, we have considered 3 roles − Admin, Guest, and User. Let us create a collection with documents −

> db.demo532.insertOne({"Name":"Chris","Type":"Admin"});{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e8b4a9def4dcbee04fbbbf9")
}
> db.demo532.insertOne({"Name":"David","Type":"Guest"});{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e8b4aa3ef4dcbee04fbbbfa")
}
> db.demo532.insertOne({"Name":"Bob","Type":"User"});{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e8b4ab0ef4dcbee04fbbbfb")
}

Display all documents from a collection with the help of find() method −

> db.demo532.find();

This will produce the following output −

{ "_id" : ObjectId("5e8b4a9def4dcbee04fbbbf9"), "Name" : "Chris", "Type" : "Admin" }
{ "_id" : ObjectId("5e8b4aa3ef4dcbee04fbbbfa"), "Name" : "David", "Type" : "Guest" }
{ "_id" : ObjectId("5e8b4ab0ef4dcbee04fbbbfb"), "Name" : "Bob", "Type" : "User" }

Following is the query to get a unique document which needs to be compared with other documents in the same collection −

> db.demo532.aggregate([
...    {$group: {_id:"$Name", "types":{$addToSet:"$Type"}}},
...    {$project: {_id:1, "types": 1, "isSubset": { $setIsSubset: [ ["Admin"], "$types" ] }}},
...    {$match: {"isSubset": false}},
...    {$group: {_id:"$isSubset", "Name": {$push : "$_id"}}},
...    {$project: {"_id": 0, "Name": 1}},
...    {$unwind: "$Name"}
... ])

This will produce the following output −

{ "Name" : "David" }
{ "Name" : "Bob" }
Updated on: 2020-05-14T06:22:55+05:30

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