If you have your structure as json or xsd, you could create a mapping and let the modeler build all your entities and associations. but it is getting little mess.
You can copy all the data from any Mendix-supported database management system to any other Mendix-supported database management system. For example you can copy demo, test, and production databases from built-in to PostgreSQL, and from PostgreSQL to built-in. You can also migrate production data from SQL Server or Oracle (on-premises) to PostgreSQL in our cloud.
To do this, start your app on the database you would like to copy the data to. This database should already exist and should be totally empty. To let Mendix know from which database all data should be copied, you have to set some custom configuration settings. These custom settings identify the source database and give Mendix the authentication required to access it.