ModelsDatabasesRelationships.md

## Models, Databases, Relationships in Rails

#### What is the difference between a primary key and a foreign key? Where would we find a primary key? What would it be called by default? Where would we find a foreign key? What is the naming convention for a foreign key?
  * Primary key lives on the one side of a one to many relationship. It is generally called tablename_id. The "many" object in the relationship holds on to a forieign key that uniqely identifies it's "one" association.
#### Write down one example of:
* a `one-to-one `relationship.
  * Citizen to SSN
  * One king to one kingdom
* a `one-to-many relationship`.
  * One kingdom has many peasants
* a `many-to-many relationship`.
  * Each crop has many peasants that raised it, each peasant has many crops he/she raised
  
  
* Test database is modified and accessed when running tests
* Development databases are interacted with in the same way as the production database, but data is stored independent of production.
* Production database stores real client data

#Creating a Rails app
 * rails new project_name --database=postgresql
 
#rails g model
 *this creates a a migration file with a create_table :models command
 
#rails g migration
 *this generates a new migration that joins tables

#how to remove column
 *rails g migration RemoveColumnfromItems quantity:integer