MongoDB Connection Methods

The MongoDB connection method consist all the methods that is used to enable and disable the connection to our database.

#1. connect (url, user, password)

The connect method is used to establish a connection to a MongoDB objects. The method returns the reference to the database also. We can use the Mongo () instance and its getDB() method instead in some cases.

Example

The above query will return a reference to JTPDatabase and instantiates a fresh connection to the MongoDB objects running on the localhost interface and:

#2. Mongo(host, ClientSideFieldLevelEncryptionOptions)

The mongo is a JavaScript constructor that is used to create instances for a database connection that belongs to mongo shell or to a JavaScript file.

Example

A new connection object from the mongo shell will be created using the following query:

To interact with the mymongo.example.net:27017 cluster we will issue the below query against the cluster object:

#3. Mongo.getDB(<database>)

The getDB method is used to provides access to database objects that belongs to the mongo shell or to a JavaScript file.

Example

The above query establish a new connection to the MongoDB objects running on the localhost interface and returns a reference to "JTPDatabase":

#4. Mongo.isCausalConsistency()

As the name suggest of this method, the casual consistency is used to returns a Boolean result that indicates whether the causal consistency of the instance is enabled on the connection object.

Example

The above query determines that the causal consistency is enabled on the Mongo connection object or not, which is associated with the mongo shell's global database variable:

#5. Mongo.setCausalConsistency(<boolean>)

The setcasualconsistency() method enables or disables the causal consistency on the specified connection object. This method removes the object's connection by default.

Example

The query below enables the causal consistency on the instances of MongoDB which is associated with the mongo shell's global database variable:

If you want to check the causal consistency is enabled or not for a connection. You can use the Mongo.isCausalConsistency() method.

#6. Mongo.setReadPref(mode, tagSet)

The setReadPref method is used on a Mongo connection object to control the reaction of the client route for all queries to members of the specified replica set.

Examples

The read preference mode is used in the following example to target the read operation to a secondary member.

For specific tag secondaries will include the tag set array:

#7. Mongo.startSession(<options>)

The start session method is used to starts a session for the connection. The session id will be assigned to commands associated with the session by mongo shell.

Examples

To start a session with re-triable writes enabled, you have to use the above query that will help you enable it with causal consistency.

#8. Mongo.watch(pipeline, options)

The watch method allows us to open a changed stream cursor for the specified replica set or a specified sharded cluster. With the exception of the local, config, and the admin databases the replica set will be changed to report on all its non-system collections across the specific DB,.

Example

The query example opens a change stream cursor on a replica set of the mongoShell. Except for the admin, local, and the config databases, all databases will be reported on data changes by the returned cursor to all the non-system collections.

We can use the cursor.isExhausted() method to iterate the cursor to check for new events and ensure that the loop only exits in the case of changes made to stream cursor.

#9. Session()

The session method establishes the session object for the connection in the mongo shell. Use Mongo.startSession() to establish a session for the connection in the mongo shell,

Example

A session on the Mongo connection object will be started that is associated with the mongo shell's global database variable. After that, to retrieve the database object associated with the session, it uses the Session.getDatabase() method.