SocketException: Error connecting to 127.0.0.1:27017 :: caused by :: Connection refused

This error message is typically associated with MongoDB, a popular NoSQL database. It indicates that the application is unable to connect to the MongoDB server running on the same machine at IP address 127.0.0.1 (also known as "localhost") on port 27017.

There are several reasons why this error might occur:

1. The MongoDB server is not running: Check to make sure that the MongoDB server is running and listening on port 27017. You can check this by running the command "mongod" in a terminal window.

2. The MongoDB server is running on a different port: If the MongoDB server is running on a different port, you will need to update the connection string in your application to reflect the correct port number.

3. The MongoDB server is not accessible from the application: Make sure that there are no firewall rules or security settings that are preventing the application from connecting to the MongoDB server.

4. The application is using the wrong IP address: Double-check that the application is connecting to the correct IP address for the MongoDB server. If the server is running on a different machine, you will need to update the connection string accordingly.

To resolve this issue, you will need to identify the root cause of the connection problem and take appropriate action.