Deleting Documents from a Collection

At times you may need to delete documents from your MongoDB collection to control space consumption, improve performance, and keep things clean. The remove() method on Collection objects makes it very simple to delete documents from a collection. The syntax for the remove() method is shown below:

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remove([query], [options], [callback])

The query parameter is a document that is used to identify which document(s) you want to delete. The request matches the properties and values in query with the fields and values of the object, and only those that match the query are updated. If no query is provided, then all the documents in the collection are deleted.

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 options. The first parameter of callback is an error, and the second parameter is a count of the documents that were deleted.

Listing 14.7 uses the remove() method to delete objects from a collection. In lines 9–18, remove() and callback query the collection for documents whose type is planetary and deletes them from the collection. Notice that the results parameter of callback is the count of documents deleted. Figure 14.7 shows the output of Listing 14.7.

Listing 14.7 doc_delete.js: Deleting documents from a collection

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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.find(function(err, items){
06       items.toArray(function(err, itemArr){
07         console.log("Before Delete: ");
08         console.log(itemArr);
09         nebulae.remove({type:"planetary"}, function(err, results){
10           console.log("Deleted " + results + " documents.");
11           nebulae.find(function(err, items){
12             items.toArray(function(err, itemArr){
13               console.log("After Delete: ");
14               console.log(itemArr);
15               db.close();
16             });
17           });
18         });
19       });
20     });
21   });
22 });

Figure 14.7 Deleting documents from a collection.