4. Low-level API

GMongo is a simple Groovy wrapper around the regular Mongo Java Driver. In general you can refer to the Mongo Java Drivers Javadoc API when using GMongo.

GMongo provides some nice enhancements like easy access to collections using the dot operator and support for Groovy operator overloading.

There is an excellent tutorial on how to use the Mongo Java driver's API directly in the Mongo documentation

An example of GMongo usage can be seen below:

// Get a db reference in the old fashion way
def db = mongo.getDB("gmongo")
// Collections can be accessed as a db property (like the javascript API)
assert db.myCollection instanceof com.mongodb.DBCollection
// They also can be accessed with array notation
assert db['my.collection'] instanceof com.mongodb.DBCollection
// Insert a document
db.languages.insert([name: 'Groovy'])
// A less verbose way to do it
db.languages.insert(name: 'Ruby')
// Yet another way
db.languages << [name: 'Python']
// Insert a list of documents
db.languages << [[name: 'Javascript', type: 'prototyped'], [name: 'Ioke', type: 'prototyped']]

To get hold of the mongo instance (which is an of the com.mongodb.Mongo class) inside a controller or service simple define a mongo property:

def mongo
def myAction = {
    def db = mongo.getDB("mongo")
    db.languages.insert([name: 'Groovy'])
}

A request scoped bean is also available for the default database (typically the name of your application, unless specified by the databaseName config option, plus the suffix "DB").

def peopleDB
def myAction = {
    peopleDB.languages.insert([name: 'Fred'])
}

Each domain class you define also has a collection property that allows easy access to the underlying DBCollection instance and hence the GMongo API:

Person.collection.count() == 1
Person.collection.findOne(firstName:"Fred").lastName == "Flintstone"

If you are using Hibernate entities with Mongo then the collection will be scoped in the mongo namespace. Example: Person.mongo.collection.count()