Tutorial :Update values in array in MongoDB



Question:

I'm trying to come up with a way to update the values in an array of objects in mongo. I have a collection which looks like

   [       { CourseName: '',         Sessions: [                {                   _id: null, //oops I didn't set this in the import                   Name: 'blah',                   Location: 'moon'                }]       }      ]  

Now I need to set the _id field. I tried the documented approach of doing

db.Course.update({'Sessions._id': null}, {$set:{'Sessions.$._id': ObjectId()}}, false, true)  

But I ran into this bug http://jira.mongodb.org/browse/SERVER-1055 which meant that I couldn't do it. Is there some syntax which will allow me just to itterate over the collection and update each record by hand? I tried a few things like

db.Course.find().forEach(      function(course)       {          course.Sessions.forEach(function(session)              {                  session._id=ObjectId();                  course.Save(session); //Don't know how to save a single object              });      });  

but they didn't work. I'm looking for some way to just update that value in each session.


Solution:1

I think what you want is:

db.Course.find().forEach(      function(course)       {          course.Sessions.forEach(function(session)              {                  session._id=ObjectId();              });          db.Course.save(course);      });  

However, you can run into problems saving stuff into a collection you're in the middle of iterating over, so I'd suggest loading a bunch of documents into an array, processing them, loading another batch, etc.


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