node.js - Mongo/Mongoose: cleanup orphaned refs -

suppose typical one-to-many relationship modeled using references suggested mongodb official documentation:

var user = mongoose.schema({  });  var group = mongoose.schema({    user: [{     type: mongoose.schema.types.objectid,     ref: 'user'   }]  }); 

let's assume care order, in users appear in group, array necessary.

now, let's assume user has been deleted -- , groups have not been maintained $pull reason. if use mongoose's populate looks fine, garbage persists in array.

is there way identify orphaned refs , remove them? maybe automatically -- cascade in relational world? what's best approach maintain referential integrity in mongo/mongoose? finally, what's efficient one?

first, use remove hook on user model try maintain data integrity on ongoing basis: user.post('remove', pulluserfromgroups); keep integrity intact. can remove user every group single $pull operation. mongo analog cascade relational dbs.

for after-the fact cleanup need iterate on every group, find every userid in group.user, query see if record exists, , pull out if not. it's simplest 1 @ time, use user.find({_id: {$in: group.user}}) , calculate user ids not found , pull them way.