What You’ll Learn in This Hour:
Inserting new documents into a collection from Node.js
Removing documents from a collection in Node.js
Getting, manipulating, and saving a single document in a collection from Node.js
Updating documents in a collection from Node.js
Performing an upsert operation from Node.js
Continuing from the last hour, this hour describes the Node.js MongoDB driver and shows how to implement it to add, manipulate, and remove documents from a collection in your Node.js applications. Several methods are available for changing data in a collection. You can insert new documents, update existing documents using update or save, remove old documents, and apply an upsert (which first tries to update documents and, if it finds none, then inserts a new one).
The following sections cover the various methods on the Node.js Collection
object that enable you to manipulate data in the collection. You see how to insert, delete, save, and update documents in a collection from your Node.js application.
An important task when interacting with MongoDB databases from Node.js is inserting documents into collections. To insert a document, you need to first create a JavaScript object that represents the document that you want to store. Insert operations pass the JavaScript object to the MongoDB sever as a BSON that you can insert into the collections.
When you have a JavaScript object version of your new document, you can store it in the MongoDB database using the insert()
method on an instance of the Collection
object that is connected to the database. The following shows the syntax for the insert()
method, where the doc
parameter can be a single document object:
insert(doc, callback)
For example, the following shows an example of inserting a single document and an array of documents into a collection:
var doc1 = {'name' : 'Fred'};
myColl.insert(doc1, function(err, results){
. . .
});
To insert multiple documents into your collection, you can pass an array of JavaScript objects to the insert()
method on the Collection
object. For example:
var doc2 = {'name' : 'George'};
var doc3 = {'name' : 'Ron'};
myColl.batchInsert([doc2, doc3], function(err, results){
. . .
});
The insert()
method returns the newly created documents as JavaScript objects. These objects contain the new _id
value generated by the server.
You will need to delete documents from your MongoDB collection from Node.js to keep space consumption down, improve performance, and keep things clean. The remove()
method on Collection
objects makes it simple to delete documents from a collection. The syntax for the remove()
method follows:
remove([query], callback)
The query
parameter is a JavaScript object that identifies which document(s) you want to delete. The request matches the fields and values in the query
with the fields and values of the object, and only those that match the query are updated. If no query
is provided, all the documents in the collection are deleted.
For example, to delete all documents in the words_stats
collection, you would use
collection.remove(function(err, results){
. . .
});
The following code deletes all words that start with a
from the words_stats
collection:
var query = {'first' : 'a'};
collection.remove(query, function(err, results){
. . .
});
The remove()
method returns a count of the documents deleted as the second parameter to the callback function.
A convenient method of updating objects in the database is to use the save()
method on Collection
objects. The save
method accepts a JavaScript object as a parameter and saves it to the database. If the document already exists in the database, it is updated with the new values. If the document does not already exist in the database, a new document is created.
The following shows the syntax of the save()
method, where the doc
parameter is the JavaScript object representing the document to be saved to the collection:
save(doc, callback)
The save()
method returns a count of the documents saved as the second parameter to the callback function.
After objects have been inserted into a collection, you often need to update them from Node.js as data changes. The update()
method on the Collection
object enables you to update documents in a collection. The update
method is versatile yet fairly easy to implement. The following shows the syntax for the update()
method:
update(query, update, [options], callback)
The query
parameter is a JavaScript object that identifies which document(s) you want to change. The request matches the properties and values in the query with the fields and values of the object, and only those that match the query are updated. The update
parameter is a JavaScript object that specifies the changes to make to the documents that match the query. Hour 8, “Manipulating MongoDB Documents in a Collection,” describes the update operators used in this object.
The options
parameter enables you to set specific options for write concern and for update operations. For update()
operations, you need to be aware of the upsert
and multi
parameters. The upsert
parameter is a Boolean that determines whether an upsert
operation should be done; if it is true
and no documents match the query, a new document is inserted into the collection. The multi
parameter is also a Boolean. When true, the update
operation is applied to all documents that match the query; otherwise, only the first document is updated.
For example, the following changes the category
field value to old
for items in the collection for which category
currently is new
. With upsert
set to false
, new documents are not created even if no documents have a category of new
. With multi
set to true
, all documents that match are updated:
var query = {'category' : 'New'};
var update = {'$set' : {'category' : 'Old'}};
var options = {'upsert': false, 'multi': true};
myColl.update(query, update, options, function(err, results){
. . .
});
The update()
method returns a count of the documents saved as the second parameter to the callback function.
Another way to use the update()
method on the Collection
object in Node.js is to use an upsert operation. An upsert operation first tries to update documents in the collection. If no documents match the update query, the $set
operator creates a new document and adds it to the collection. The following shows the syntax for the update()
method:
update(query, update, [options], callback)
The query
parameter identifies which document(s) you want to change. The update
parameter is a JavaScript object that specifies the changes to make to the documents that match the query. For upsert operations, the upsert
option should be set to true
and the multi
option should be set to false
.
For example, the following performs an upsert on a document with name=myDoc
. The $set
operator defines the fields used to create or update the document. With upsert
set to true
, if the document is not found, it is created; otherwise, it is updated.
var query = {'name': 'myDoc'};
var setOp = {'name': 'myDoc',
'number', 5,
'score', 10};
var update = {'$set': setOp};
var options = {'upsert': true, 'multi': false};
update(query, update, options, function(err, results){
. . .
});
In this hour, you used the Node.js MongoDB driver to add, manipulate, and remove documents from a collection in your Node.js applications. You used several different methods on the Collection
object to change data in a collection.
The insert()
method adds new documents. The remove()
method deletes documents. The save()
method updates a single document.
You can use the update()
method in multiple ways. You can have it update a single document or multiple documents. You can also apply the upsert option to insert new documents into the collection if none matches.
Q. Is it possible to read documents from the cursor as a Node.js-readable stream?
A. Yes. The Node.js MongoDB driver provides the CursorStream()
class, which converts a Cursor
object into a readable stream object.
The workshop consists of a set of questions and answers designed to solidify your understanding of the material covered in this hour. Try answering the questions before looking at the answers.
1. Which operation do you use from a Node.js application to create a new document if one does not exist?
2. How do you limit the update()
method to only a single document?
3. True or false: You can use the save()
method on Collection
objects only to save existing documents.
4. What type of parameter defines the fields to update in the update()
method of the Collection
object?
1. Use the update()
method on the Collection
object with upsert
set to true
.
2. Set the multi
parameter to false
.
3. False. save()
adds the document if it doesn’t exist.
4. It is a JavaScript object that contains MongoDB update operators as fields.
1. Find a new word that you want to add to the word_stats
collection in the example dataset. Write a new Node.js application similar to the Node.jsDocAdd.js
file to add that word.
2. Create a new Node.js application that uses the update()
method to update all words with first letter of e
and add the category of eWords
to them.
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