- Write SQLAlchemy migrations.
- Connect between tables using SQLAlchemy relationships.
- Use SQLAlchemy to run CRUD statements in the database.
- Schema: the blueprint of a database. Describes how data relates to other data in tables, columns, and relationships between them.
- Persist: save a schema in a database.
- Engine: a Python object that translates SQL to Python and vice-versa.
- Session: a Python object that uses an engine to allow us to programmatically interact with a database.
- Transaction: a strategy for executing database statements such that the group succeeds or fails as a unit.
- Migration: the process of moving data from one or more databases to one or more target databases.
For this assignment, we'll be working with a freebie domain.
As developers, when you attend hackathons, you'll realize they hand out a lot of free items (informally called freebies, or swag)! Let's make an app for developers that keeps track of all the freebies they obtain.
We have three models: Company
, Dev
, and Freebie
For our purposes, a Company
has many Freebie
s, a Dev
has many Freebie
s,
and a Freebie
belongs to a Dev
and to a Company
.
Company
- Dev
is a many to many relationship.
Note: You should draw your domain on paper or on a whiteboard before you start coding. Remember to identify a single source of truth for your data.
To get started, run pipenv install && pipenv shell
while inside of this
directory.
Build out all of the methods listed in the deliverables. The methods are listed in a suggested order, but you can feel free to tackle the ones you think are easiest. Be careful: some of the later methods rely on earlier ones.
Remember! This mock code challenge does not have tests. You cannot run
pytest
and you cannot run learn test
. You'll need to create your own sample
instances so that you can try out your code on your own. Make sure your
relationships and methods work in the console before submitting.
We've provided you with a tool that you can use to test your code. To use it,
run python debug.py
from the command line. This will start an ipdb
session
with your classes defined. You can test out the methods that you write here. You
are also encouraged to use the seed.py
file to create sample data to test your
models and associations.
Writing error-free code is more important than completing all of the deliverables listed- prioritize writing methods that work over writing more methods that don't work. You should test your code in the console as you write.
Similarly, messy code that works is better than clean code that doesn't. First, prioritize getting things working. Then, if there is time at the end, refactor your code to adhere to best practices.
Before you submit! Save and run your code to verify that it works as you expect. If you have any methods that are not working yet, feel free to leave comments describing your progress.
The starter code has migrations and models for the initial Company
and Dev
models, and seed data for some Company
s and Dev
s. The schema currently looks
like this:
Column | Type |
---|---|
name | String |
founding_year | Integer |
Column | Type |
---|---|
name | String |
You will need to create the migration for the freebies
table using the
attributes specified in the deliverables below.
Write the following methods in the classes in the files provided. Feel free to build out any helper methods if needed.
Remember: SQLAlchemy gives your classes access to a lot of methods already! Keep in mind what methods SQLAlchemy gives you access to on each of your classes when you're approaching the deliverables below.
Before working on the rest of the deliverables, you will need to create a
migration for the freebies
table.
- A
Freebie
belongs to aDev
, and aFreebie
also belongs to aCompany
. In your migration, create any columns yourfreebies
table will need to establish these relationships using the right foreign keys. - The
freebies
table should also have:- An
item_name
column that stores a string. - A
value
column that stores an integer.
- An
After creating the freebies
table using a migration, use the seed.py
file to
create instances of your Freebie
class so you can test your code.
After you've set up your freebies
table, work on building out the following
deliverables.
Use SQLAlchemy's ForeignKey
, relationship()
, and backref()
objects to
build relationships between your three models.
Note: The plural of "freebie" is "freebies" and the singular of "freebies" is "freebie".
Freebie.dev
returns theDev
instance for this Freebie.Freebie.company
returns theCompany
instance for this Freebie.
Company.freebies
returns a collection of all the freebies for the Company.Company.devs
returns a collection of all the devs who collected freebies from the company.
Dev.freebies
returns a collection of all the freebies that the Dev has collected.Dev.companies
returns a collection of all the companies that the Dev has collected freebies from.
Use python debug.py
and check that these methods work before proceeding. For
example, you should be able to retrieve a dev from the database by its
attributes and view their companies with dev.companies
(based on your seed
data).
Freebie.print_details()
should return a string formatted as follows:{dev name} owns a {freebie item_name} from {company name}
.
Company.give_freebie(dev, item_name, value)
takes adev
(an instance of theDev
class), anitem_name
(string), and avalue
as arguments, and creates a newFreebie
instance associated with this company and the given dev.- Class method
Company.oldest_company()
returns theCompany
instance with the earliest founding year.
Dev.received_one(item_name)
accepts anitem_name
(string) and returnsTrue
if any of the freebies associated with the dev has thatitem_name
, otherwise returnsFalse
.Dev.give_away(dev, freebie)
accepts aDev
instance and aFreebie
instance, changes the freebie's dev to be the given dev; your code should only make the change if the freebie belongs to the dev who's giving it away