How do I update a subfield of which I know everythig, but don't know the field its a child to?

Question

How do I update a subfield of which I know everythig, but don't know the field its a child to?

I have this collection: {_id, list}

I have the elements in the list, of which each has an _id of its own, but I can't figure out how to update all the elements in the list. I do know that all collections have unique elements in the list, including amongst themselves. And I have the elements with updated properties :|

Hope I explained it clearly.

node.js
mongodb

Answer 1

I hope I've got your problem right.

Suppose, you want to update given sub-document in the list by its _id, but you don't know its parent's _id.

To make an update operation you may use the following command:

db.collection.update({
  'list._id': subdoc_id
},{
  $set: {
    'list.$.field1': value1,
    'list.$.field2': value2,
    'list.$.field3': value3
  }
})

To replace an old sub-document with the new one (equivalent of save):

db.collection.update({
  'list._id': subdoc._id
},{
  $set: {
    'list.$': subdoc
  }
})

But you should be aware that this operation will completely erase the old sub-document and replace it with the new one. So, any field not listed in subdoc will be deleted.

{'list._id': subdoc_id} query will find you a parent document containing the given sub-document and 'list.$' selector will point to the queried sub-document.

Update: If you don't know in wich particular list the given sub-document is stored, you'll need to run an update operation on each:

['list1', 'list2', 'nested.list'].forEach(function (list) {
  var query = {};
  query[list+'._id'] = subdoc._id;
  var update = { $set: {} };
  update.$set[list+'.$'] = subdoc;
  db.collection.update(query, update);
})

An update will be performed on each list where the given sub-document is present.