How do i get all keys in Mongodb collection? - mongodb

Question

I saw few solutions but those are not exact my solution. I have a DB with name results and collection name is marks like below:
db.marks.find();
{ "_id" : ObjectId("54f57522627af4bfdcf79764"), "name" : "John", "scroe1" : 23, "score2" : 21, "score5" : 12 }
{ "_id" : ObjectId("54f5761a627af4bfdcf79765"), "name" : "Mike", "scroe2" : 22, "score3" : 20, "score4" : 22 }
{ "_id" : ObjectId("559d0bc521cb2e056507c3e3"), "name" : "Bush", "score2" : 30 }
I tried with
var doc=db.marks.findOne(); for (var key in doc) print(key);
and i got
_id
name
score1
score2
score5
But i Want all keys in collection like below:
_id, name, score1, score2, score3, score4, score5
name
scroe1
score2
score3here

Answer 1

findOne will only return the first found document. Since the first document you list does not have the score3 and score4 keys, it will not display them. If you want to show all root-level keys across all documents, you would need to iterate through all the documents in the db.
var keys = [];
db.marks.find().forEach(function(doc){
for (var key in doc){
if(keys.indexOf(key) < 0){
keys.push(key);
}
}
});
print(keys);

Answer 2

mr = db.runCommand({
"mapreduce" : "my_collection",
"map" : function() {
for (var key in this) { emit(key, null); }
},
"reduce" : function(key, stuff) { return null; },
"out": "my_collection" + "_keys"
})
Then run distinct on the resulting collection so as to find all the keys:
db[mr.result].distinct("_id")
["foo", "bar", "baz", "_id", ...]

Answer 3

Mongodb find() command has two arguments first one is query and second is projections.
Something like db.collection.find(query,projection).
if the document is db.myCol.find();, then it returns:
{
{
_id:1
name: ''hello',
age: 23
}, {
_id:2
name: ''bollo',
age: 27
}
}
And db.myCol.find({},{_id:1}); returns:
1
2