Print parent column name - sqlalchemy

Question

Given the following codes:
from flask import Flask, jsonify
from flask_sqlalchemy import SQLAlchemy
app = Flask(__name__)
app.config["SQLALCHEMY_ECHO"] = True
app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False
app.config["SQLALCHEMY_DATABASE_URI"] = "sqlite:///test.db"
db = SQLAlchemy(app)
class File(db.Model):
__tablename__ = "file"
_id = db.Column(db.String, primary_key=True)
file_name = db.Column(db.String)
category_id = db.Column(db.String, db.ForeignKey("category._id"))
def as_dict(self):
return {c.name: getattr(self, c.name) for c in self.__table__.columns}
class Category(db.Model):
__tablename__ = "category"
_id = db.Column(db.String, primary_key=True)
name = db.Column(db.String)
files = db.relationship("File", backref="category")
def as_dict(self):
return {c.name: getattr(self, c.name) for c in self.__table__.columns}
db.drop_all()
db.create_all()
categories0 = Category(_id="aca50a26-5d3f-4c4d-872b-83b663d5304f",name="Apple")
files0 = File(_id="8a95ba11-e2aa-407d-bac9-609e6c559731",file_name="8a95ba11-e2aa-407d-bac9-609e6c559731.jpg",category=categories0)
db.session.add_all([categories0,files0])
db.session.commit()
results=db.session.query(File).join(Category, File.category).filter(Category._id=="aca50a26-5d3f-4c4d-872b-83b663d5304f").all()
#app.route('/print')
def printMsg():
return jsonify([c.as_dict() for c in results])
if __name__ == '__main__':
app.run(debug=True)
When I call the endpoint /print, it returns
[
{
"_id": "8a95ba11-e2aa-407d-bac9-609e6c559731",
"category_id": "aca50a26-5d3f-4c4d-872b-83b663d5304f",
"file_name": "8a95ba11-e2aa-407d-bac9-609e6c559731.jpg"
}
]
But I need the category_name as output
[
{
"_id": "8a95ba11-e2aa-407d-bac9-609e6c559731",
"category_id": "aca50a26-5d3f-4c4d-872b-83b663d5304f",
"category_name": "Apple",
"file_name": "8a95ba11-e2aa-407d-bac9-609e6c559731.jpg"
}
]
How should I achieve that?

Answer 1

Here's code working as you requested. There is some other help I'll offer in here...
You code iterated columns. That's the Database's view of things. You should iterate the attributes of the model. In many cases, they're the same for fields (not always). But for relationships, you HAVE to be looking at the model.
Instead of pulling the related attribute into the dictionary of fields, I offer a 2nd solution to NEST the related fields in the response. As your models grow and scale, you will appreciate this more than you may now.
I changed some formatting for PEP8. Even for SO posts, it helps readability and its always good practice.
I would STRONGLY consider you DO NOT use either of these solutions. Serialization is a tricky process. For simple fields/relationships like your example, it may not seem that way. Again, as you scale, you will be handling a lot of edge cases and writing code that's been written and tested many time before. Consider using Marshmallow / Flask-Marshmallow. It's a great library that makes serialization and relationship nesting trivial.
from flask import Flask, jsonify
from flask_sqlalchemy import SQLAlchemy
import sqlalchemy as sa
app = Flask(__name__)
app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///:memory:'
db = SQLAlchemy(app)
class File(db.Model):
__tablename__ = 'file'
_id = db.Column(
db.String,
primary_key=True,
)
file_name = db.Column(db.String, )
category_id = db.Column(
db.String,
db.ForeignKey('category._id'),
)
def as_dict(self):
"""Return serialzed attributes + related category name"""
serialized = {
attr.key: getattr(self, attr.key)
for attr in sa.orm.class_mapper(self.__class__).iterate_properties
if isinstance(attr, sa.orm.properties.ColumnProperty)
}
serialized['category_name'] = self.category.name
return serialized
def as_dict_with_relationships(self):
"""Return serialzed attributes + nested relationships"""
serialized = {}
for attr in sa.orm.class_mapper(self.__class__).iterate_properties:
if isinstance(attr, sa.orm.properties.ColumnProperty):
serialized[attr.key] = getattr(self, attr.key)
elif isinstance(attr, sa.orm.relationships.RelationshipProperty):
serialized[attr.key] = getattr(self, attr.key).as_dict()
else:
print(f'not handling {attr}, {type(attr)}')
return serialized
class Category(db.Model):
__tablename__ = 'category'
_id = db.Column(
db.String,
primary_key=True,
)
name = db.Column(db.String, )
files = db.relationship(
'File',
backref='category',
)
def as_dict(self):
return {
c.name: getattr(self, c.name)
for c in self.__table__.columns
}
db.drop_all()
db.create_all()
categories0 = Category(
_id='aca50a26-5d3f-4c4d-872b-83b663d5304f',
name='Apple',
)
files0 = File(
_id='8a95ba11-e2aa-407d-bac9-609e6c559731',
file_name='8a95ba11-e2aa-407d-bac9-609e6c559731.jpg',
category=categories0,
)
db.session.add_all([categories0, files0])
db.session.commit()
#app.route('/print')
def print_msg():
"""Return serialized results- top level attributes + explicit other data"""
results = db.session.query(File) \
.join(Category, File.category) \
.filter(
Category._id == 'aca50a26-5d3f-4c4d-872b-83b663d5304f',
) \
.all()
return jsonify([
record.as_dict()
for record in results
])
def print_msg2():
"""Return serialized results- top level attributes + nested relationships"""
results = db.session.query(File) \
.join(Category, File.category) \
.filter(
Category._id == 'aca50a26-5d3f-4c4d-872b-83b663d5304f',
) \
.all()
return jsonify([
record.as_dict_with_relationships()
for record in results
])
if __name__ == '__main__':
app.run(debug=True)