Saving Documents in a Collection

The save() method on Collection objects is kind of interesting. You can use it to insert or update a document in a database. Although it is not as efficient as insert() or update(), the save() method is easier to implement in some circumstances. For example, when you are making ad hoc changes to objects already retrieved from a MongoDB database, you can use save() without having to implement the query and update objects of the update() method.

The following is the syntax of the save() method:

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save(doc, [options], [callback])

The doc parameter is the document object you want to save to the collection. The options parameter specifies the database change options described in Table 14.1. The callback parameter is required if you are implementing a write concern in the options. The first parameter of the callback parameter is an error, and the second parameter is the object that was just saved to the collection.

Typically when you use save(), the document object is either a completely new JavaScript object that you want to add to the collection or an object you have already gotten back from the collection and made changes to, and you want to save those changes back to the database.

Listing 14.5 retrieves an object from the database, modifies it, and saves it back to the database, using the save() method. Lines 9–15 implement the save() method and callback. Notice that the save() method is much simpler to use than the update() and findAndModify() methods. Also notice that savedItem is returned to the callback function and displayed on the console, as shown in Figure 14.5.

Listing 14.5 doc_save.js: Updating and saving an existing document by using save()

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01 var MongoClient = require('mongodb').MongoClient;
02 MongoClient.connect("mongodb://localhost/", function(err, db) {
03   var myDB = db.db("astro");
04   myDB.collection("nebulae", function(err, nebulae){
05     nebulae.findOne({type:"supernova"}, function(err, item){
06       console.log("Before Save: ");
07       console.log(item);
08       item.info = "Some New Info";
09       nebulae.save(item, {w:1}, function(err, results){
10         nebulae.findOne({_id:item._id}, function(err, savedItem){
11           console.log("After Save: ");
12           console.log(savedItem);
13           db.close();
14         });
15       });
16     });
17   });
18 });

Figure 14.5 Updating and saving an existing document by using save().