mongodb default configuration in spring boot

I'm trying to integrate mongodb to my spring boot application. I create a db aptly named "mydb" and was wondering how mongodb classes were able to connect to my database without any configuration and why they were not retrieving my data. Answer to both is of course "default configuration" for mongodb.

You can see mongodb defaults that spring boot uses:

host: localhost
port: 27017
db: test

My mongodb is at localhost:27017, but as I'm using "mydb" instead of "test" no data is retrieved. So I have to override the default configuration by adding

spring.data.mongodb.uri=mongodb://localhost:27017/mydb

to my application.properties file.