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 is the main key that determines the identity or uniqueness of the entry in a table Foreign key is the primary key for another table that is directly related to the current table

Write down one example of:

• a one-to-one relationship.

• spouse-to-spouse

• marriage-to-divorce

• person-to-ssn

• a one-to-many relationship.

• mother-to-childern

• fridge-to-food

• turing-to-student

• landlord to tenant

• a many-to-many relationship.

• recipe-to-ingredients

• musicians-to-albums

• restaurant-server-to-restaurant-patriots

• What's the difference between test, development, and production databases?

• development database is used for the building of an specific part of the application
• production database is a process that you would not want to modify because by this stage most databases have valuable content that you would not want to get rid of.
• test database is used for testing a specific state of a application.

• How do you create a Rails app from the command line with a postgres database?

• go to the folder in which you would like your project in and type the following rails new <project_name> --database=postgresql

• What files are created by typing rails g model ...?

• the g stands for generate, rails generate model Author first_name:text last_name:text so this is broken down by rails (generating a model) based on a Author in which the Author has to columns to keep track of the first_name and last_name the : represent the type of content in this example it is a text.
  The result is that this command creates a model, migrate, yaml database, and test files.

• What is the difference between rails g model ... and rails g migration...?
  • rails g model allows the user to generate model, a migration, and two files related to testing.
  • rails g migration creates the migration and models seperately

*Imagine that the items table has a category called quantity. What command would you type if you wanted to get rid of the quantity attribute?

• rails g migration RemoveQuantityColumninItems quantity:integer

• Imagine that you have a table students. What is the ActiveRecord query that would return all students with the first name of Richard?

  • Students.find(first_name: "Richard"

• How would you update the student record with ID 4 to have a new phone number of "101-222-3333"?

  • Students.find_by(id: ID4).update(phone_number:"101-222-3333")