mongo query help using save method

[Ns Kumar]

Case1:

MongoDB Enterprise > db.coll.insert({x:1})

WriteResult({ "nInserted" : 1 })

MongoDB Enterprise > db.coll.find()

{ "_id" : ObjectId("5a0581f21ef47834e0281945"), "x" : 1 }

MongoDB Enterprise > var j = db.coll.findOne()

MongoDB Enterprise > j

{ "_id" : ObjectId("5a0581f21ef47834e0281945"), "x" : 1 }

MongoDB Enterprise > j.y=2

2

MongoDB Enterprise > j

{ "_id" : ObjectId("5a0581f21ef47834e0281945"), "x" : 1, "y" : 2 }

MongoDB Enterprise > db.coll.save(j)

WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })

MongoDB Enterprise > db.coll.find()

{ "_id" : ObjectId("5a0581f21ef47834e0281945"), "x" : 1, "y" : 2 }

Case2:

MongoDB Enterprise > var j = db.coll.find({x:1})

MongoDB Enterprise > j

{ "_id" : ObjectId("5a0581f21ef47834e0281945"), "x" : 1, "y" : 2 }

MongoDB Enterprise > j.z=3

3

MongoDB Enterprise > db.coll.save(j)

2017-11-10T16:11:26.377+0530 E QUERY    [thread1] Error: can't save a DBQuery object :

DBCollection.prototype._validateObject@src/mongo/shell/collection.js:231:15

DBCollection.prototype._validateForStorage@src/mongo/shell/collection.js:245:5

Bulk/this.insert@src/mongo/shell/bulk_api.js:652:17

DBCollection.prototype.insert@src/mongo/shell/collection.js:344:13

DBCollection.prototype.save@src/mongo/shell/collection.js:596:16

@(shell):1:1

The only difference between case1 and case2 is the way value is stored in var j. Can someone pls help understand what is wrong in case2 that i am unable to save the document. Thanks in advance.

[Kevin Adistambha]

Hi

The difference is that in case 1 you’re using db.collection.findOne() which returns a document, and in case 2 you’re using db.collection.find() which returns a cursor. See:

• db.collection.find()
• db.collection.findOne()

Since db.collection.save() expects a document as parameter, it prints an error when you called it using a cursor.

Best regards,
Kevin

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