Question

I have the following collection:

{ 
"Milestones" : [      
    {       "ActualDate" : null,   
    "Index": 0,
    "Name" : "milestone1",  
    "TargetDate" : ISODate("2011-12-13T22:00:00Z"),         
    "_id" : ObjectId("4ee89ae7e60fc615c42e28d1")},         
    {       "ActualDate" : null,    
    "Index" : 0,    
    "Name" : "milestone2",  
    "TargetDate" : ISODate("2011-12-13T22:00:00Z"),         
    "_id" : ObjectId("4ee89ae7e60fc615c42e28d2") } ]
, 
"Name" : "a", "_id" : ObjectId("4ee89ae7e60fc615c42e28ce") 
}

I want to update definite documents: that have specified _id, List of Milestones._id and ActualDate is null.
I dotnet my code looks like:

var query = Query.And(new[] { Query.EQ("_id", ObjectId.Parse(projectId)),
  Query.In("Milestones._id", new BsonArray(values.Select(ObjectId.Parse))), 
 Query.EQ("Milestones.ActualDate", BsonNull.Value) });                

var update = Update.Set("Milestones.$.ActualDate", DateTime.Now.Date);    

Coll.Update(query, update, UpdateFlags.Multi, SafeMode.True);

Or in native code:

db.Projects.update({ "_id" : ObjectId("4ee89ae7e60fc615c42e28ce"), "Milestones._id" : { "$in" : [ObjectId("4ee89ae7e60fc615c42e28d1"), ObjectId("4ee89ae7e60fc615c42e28d2"), ObjectId("4ee8a648e60fc615c41d481e")] }, "Milestones.ActualDate" : null },{ "$set" : { "Milestones.$.ActualDate" : ISODate("2011-12-13T22:00:00Z") } }, false, true)

But only the first item is being updated.

Answer 1

This is not possible in current moment. Flag multi in update means update of multiple root documents. Positional operator can match only one nested array item. There is such feature in mongodb jira. You can vote up and wait.

Current solution can be only load document, update as you wish and save back or multiple atomic update for each nested array id.

From documentation at mongodb.org:

Currently the $ operator only applies to the first matched item in the
query