## Database Persistence ##
The persistence package includes classes to store different class objects in a Postgres database.

### models ###
This defines models for all class objects that we want to persist. It is used for Object Relation Mapping (ORM)
of the class objects to database table columns

### repositories ###
This defines repository classes that contain CRUD methods for database operations.

### config_db ##
This Python file is a configuration class that contains variables that map to configuration parameters in a .env file. 
It also contains a method ``def conn_string()`` which returns the connection string to a Postgres database.

### Base ##
This class has a constructor that establishes a database connection and returns a reference for database-related CRUD operations.

### db_migration ###
This Python file is in the root of Hub and should be run to create all the required Postgres database tables

### Database Configuration Parameter ###
A .env file (or environment variables) with configuration parameters described below are needed to establish a database connection:
```
DB_USER=postgres-database-user
DB_PASSWORD=postgres-database-password
DB_HOST=database-host
DB_PORT=database-port
```