Is there an operator I could use in aggregate function to get a string instead of ObjectId in response?
db.something.aggregate([
{ "$match": { "property": { "$exists": true } } },
{ "$project": { "stringId": "$_id.???" } }
])
3 Answers
Mongodb 4.0 has introduced $toString aggregation operator. So, Now you can easily convert ObjectId to string
db.collection.aggregate([
{
$project: {
_id: {
$toString: "$_id"
}
}
}
])
OR vice versa using $toObjectId aggregation
db.collection.aggregate([
{
$project: {
_id: {
$toObjectId: "$_id"
}
}
}
])
6 Comments
Charlie
How about in Mongodb version 3.6?
Ashh
@Charlie No you can't. You have to upgrade to 4.0 and that's what always been intresting about the new versions.
Boat
But how to do this in version 3.9 ?
Ashh
@Boat Mongodb has not introduced any 3.9 version. Are you talking about any driver version? or mongodb 3.6.9?
Ashh
@Boat Then have a look at second comment.
|
There is no Direct Operator in aggregate function to get String from ObjectId.
After version 2.6 You can use ObjectId.toString() method to convert your ObjectId to string. First you match and project your ObjectID. Then you can convert this object ID to string by using ObjectID.toString().
db.something.aggregate([{"$match":{'property': {$exists:true}}},{"$project":{"_id":1}}])
And then use resulting Object and get the string as response using ObjectID.tostring()
Edit: You can access the str attribute of the object id using
ObjectId("507f191e810c19729de860ea").strsource: mongodb docs
Comments
You can do it inline using the $concat operator:
db.something.aggregate(
[
{ $match :
{ 'property' :
{ $exists:true }
}
},
{ $project:
{ stringId:
{ $concat: [ ObjectId().str ] }
}
}
]
)
2 Comments
mcdave
For me, this doesn't make "stringId" the ObjectId of the record. It makes it a stringified version of a brand new ObjectId. In particular, it's the same value for all the documents returned. So I don't think this is right.
Nicholas Hamilton
lol fail ......
$substrand numeric to Date or Date to numeric is basically possible with trickery ). Why would you think this is needed anyway? It's fairly simple in most languages to write theObjectIdvalue as a string anyway.{ "$oid": "56ea9e8bb1e015d13b376db5" }since at least that lets a remote client know that the data is indeed anObjectIdso it can parse and cast correctly itself. That's a good thing, especially considering that storage is half the bytes of the string length.