Question

We have made a change in our data model and we would like to apply it to all documents in one of our collections:

{
  "id":60,
  "measurement":{
    "steps":1274.0
  },
  "date":"2012-05-15T00:00:00Z"
}

to:

{  
  "id":60,
  "measurement":{
      "distance":{
          "steps":1274.0}
      },
  "date":"2012-05-15T00:00:00Z"
}

Essentially, we want to further nest the field steps, placing it under the distance field.

As for measurement.step, we would like to convert measurement.miles to measurement.distance.miles and measurement.minutes to measurement.time.minutes.

Any thoughts and/or suggestions would be appreciated.

Answer 1

Assuming you’re asking how to script the schema change, which wasn’t quite clear in the question: I would do something like this, unless you have more cases for the document structure, or mixed cases:

// find all the measurement documents with steps
db.coll.find({"measurement.steps":{$exists:true}}).forEach(function(doc) {      
  // create a new distance subdoc with the steps
  doc.measurement.distance = {steps:doc.measurement.steps};
  // delete the old steps subdoc
  delete doc.measurement.steps;
  // save the document
  db.coll.save(doc);
});
// find all the measurement documents with miles
db.coll.find({"measurement.miles":{$exists:true}}).forEach(function(doc) {
  // create a new distance subdoc with the miles
  doc.measurement.distance = {miles:doc.measurement.miles};
  delete doc.measurement.miles;
  db.coll.save(doc);
});
// find all the measurement documents with minutes
db.coll.find({"measurement.minutes":{$exists:true}}).forEach(function(doc) {
  // create a new time subdoc with the minutes
  doc.measurement.time = {minutes:doc.measurement.minutes};
  delete doc.measurement.minutes;
  db.coll.save(doc);
});

You could pretty easily do the equivalent in the language/driver of your choice to ensure types, but it is probably faster to do in the shell. Hope it helps.