Set same value on multiple fields

You could try first creating the update object where you can set the multiple fields of that object before updating the document this way:

var days = ["mon", "tue", "wed", "thu", "fri", "sat", "sun"],    timings = {},    query = {"_id" : ObjectId("554e12e4674dec7517e692eb")},    update = {        "$set": { "timings": timings }    },    options = {"upsert": true};days.forEach(function (day){ timings[day] = "Open 24 Hours" });db.collection.update(query, update, options);

Querying the collection for that document using db.collection.findOne(query) will yield:

/* 0 */{    "_id" : ObjectId("554e12e4674dec7517e692eb"),    "timings" : {        "mon" : "Open 24 Hours",        "tue" : "Open 24 Hours",        "wed" : "Open 24 Hours",        "thu" : "Open 24 Hours",        "fri" : "Open 24 Hours",        "sat" : "Open 24 Hours",        "sun" : "Open 24 Hours"    }}

-- UPDATE --

Another approach (as suggested by @Michael in the comments) is to use the JavaScript's native Object.keys() method which returns an array of a given object's own enumerable properties, in the same order as that provided by a for...in loop (the difference being that a for-in loop enumerates properties in the prototype chain as well):

> var days = Object.keys(db.collection.findOne().timings);> print(days);mon,tue,wed,thu,fri,sat,sun>

And thus can be implemented as:

var days = Object.keys(db.collection.findOne().timings),    timings = {},    query = {"_id" : ObjectId("554e12e4674dec7517e692eb")},    update = {        "$set": { "timings": timings }    },    options = {"upsert": true};