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Conclusion of this section

Adding SQL storage to our app has required quite a few changes! Let's do a quick review.

Installed SQLAlchemy and Flask-SQLAlchemy​

pip install sqlalchemy flask-sqlalchemy

And

requirements.txt
sqlalchemy
flask-sqlalchemy

Created models​

models/item.py
from db import db


class ItemModel(db.Model):
    __tablename__ = "items"

    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(80), unique=True, nullable=False)
    price = db.Column(db.Float(precision=2), unique=False, nullable=False)

    store_id = db.Column(
        db.Integer, db.ForeignKey("stores.id"), unique=False, nullable=False
    )
    store = db.relationship("StoreModel", back_populates="items")

And

models/store.py
from db import db


class StoreModel(db.Model):
    __tablename__ = "stores"

    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(80), unique=True, nullable=False)

    items = db.relationship("ItemModel", back_populates="store", lazy="dynamic")

Updated resources to use SQLAlchemy​

Previously we were using Python dictionaries as a database. Now we've swapped them out for using SQLAlchemy models by:

  • Importing the models in our resource files
  • Retrieving models from the database with ModelClass.query.get_or_404(model_id).
  • Updating models by changing attributes, or creating new model class instances, and then saving and committing with db.session.add(model_instance) and db.session.commit().
  • Deleting models with db.session.delete(model_instance) followed by db.session.commit().

Updated marshmallow schemas​

Since now our models have relationships, that means that the schemas can have Nested fields.

The schemas that don't have Nested fields we've called "Plain" schemas, and those that do are named after the model they represent.

schemas.py
from marshmallow import Schema, fields


class PlainItemSchema(Schema):
    id = fields.Int(dump_only=True)
    name = fields.Str(required=True)
    price = fields.Float(required=True)


class PlainStoreSchema(Schema):
    id = fields.Int(dump_only=True)
    name = fields.Str()


class ItemSchema(PlainItemSchema):
    store_id = fields.Int(required=True, load_only=True)
    store = fields.Nested(PlainStoreSchema(), dump_only=True)


class ItemUpdateSchema(Schema):
    name = fields.Str()
    price = fields.Float()


class StoreSchema(PlainStoreSchema):
    items = fields.List(fields.Nested(PlainItemSchema()), dump_only=True)

And that's it! Quite a few changes, but hopefully you're still with me.

In the following sections we'll be adding more functionality to our API, so stay tuned!