How can I validate DBRefs in a MongoDB collection? - validation

Question

Assuming I've got a MongoDB instance with 2 collections - places and people.
A typical places document looks like:
{
"_id": "someID"
"name": "Broadway Center"
"url": "bc.example.net"
}
And a people document looks like:
{
"name": "Erin"
"place": DBRef("places", "someID")
"url": "bc.example.net/Erin"
}
Is there any way to validate the places DBRef of every document in the people collection?

Answer 1

There's no official/built-in method to test the validity of DBRefs, so the validation must be performed manually.
I wrote a small script - validateDBRefs.js:
var returnIdFunc = function(doc) { return doc._id; };
var allPlaceIds = db.places.find({}, {_id: 1} ).map(returnIdFunc);
var peopleWithInvalidRefs = db.people.find({"place.$id": {$nin: allPlaceIds}}).map(returnIdFunc);
print("Found the following documents with invalid DBRefs");
var length = peopleWithInvalidRefs.length;
for (var i = 0; i < length; i++) {
print(peopleWithInvalidRefs[i]);
}
That when run with:
mongo DB_NAME validateDBRefs.js
Will output:
Found the following documents with invalid DBRefs
513c4c25589446268f62f487
513c4c26589446268f62f48a

Answer 2

you could add a stored function for that. please note that the mongo documentation discourages the use of stored functions. You can read about it here
In essence you create a function:
db.system.js.save(
{
_id : "myAddFunction" ,
value : function (x, y){ return x + y; }
}
);
and once the function is created you can use it in your where clauses. So you could write a function that checks for the existence of the id in the dbRef.