MongoDB Shell Script Update all field Names where there is space in field name - mongodb

Question

Using MongoDB shell script 3.2, how can I update all fields where field names have a space replace those with underscore?
{
"Some Field": "value",
"OtherField" :"Value",
"Another Field" : "Value"
}
update the above document as below
{
"Some_Field": "value",
"OtherField" :"Value",
"Another_Field" : "Value"
}
rename field can be done with something like this
db.CollectionName.update( { _id: 1 }, { $rename: { 'nickname': 'alias', 'cell': 'mobile' } } )
Challenging part here is filter, how to come up with a filter where there is a space in field name

Answer 1

This needs a two-step approach. First, you need a mechanism to get a list of all the keys with a space in your collection. Once you get the list, construct an object that maps those keys to their renamed values. You can then use that object as your $rename operator document. Consider using mapReduce to get the list of keys with spaces.
The following mapReduce operation will populate a separate collection with all the filtered keys as the _id values:
mr = db.runCommand({
"mapreduce": "CollectionName",
"map": function() {
var regxp = /\s/;
for (var key in this) {
if (key.match(regxp)) {
emit(key, null);
}
}
},
"reduce": function() {},
"out": "filtered_keys"
})
To get a list of all the spaced keys, run distinct on the resulting collection:
db[mr.result].distinct("_id")
["Some Field", "Another Field"]
Now given the list above, you can assemble your update document by creating an object that will have its properties set within a loop. Normally your update document will have this structure:
var update = {
"$rename": {
"Some Field": "Some_Field",
"Another Field": "Another_Field"
}
}
Thus
var update = { "$rename": {} };
db[mr.result].distinct("_id").forEach(function (key){
update["$rename"][key] = key.replace(/ /g,"_");
});
which you can then use in your update as
db.CollectionName.update({ }, update, false, true );

Answer 2

Thanks to #chridam that was a excellent query.
Had to make small changes to run query, Full working query.
mr = db.runCommand({
"mapreduce": "MyCollectionName",
"map": function() {
var regxp = /\s/;
for (var key in this) {
if (key.match(regxp)) {
emit(key, null);
}
}
},
"reduce": function() {},
"out": "filtered_keys"
})
db[mr.result].distinct("_id")
var update = { "$rename": {} };
db[mr.result].distinct("_id").forEach(function (key){
update["$rename"][key] = key.replace(/\s+/g, "_");
});
//print(update)
db.MyCollectionName.update({ }, update, false, true );