将两条 sqlalchemy 语句合二为一

Question

I want to retrieve from my DB a single record, which is a question (I am building a quiz mechanism). I have the following requirements to this hit:

1. It should be a question from the quiz the user is currently playing
2. It should be a question which the user has not answered before, eg; it should not be a record in the responses table
3. The questions should be ordered by category.

The following models are involved:

Questions: Contains all questions from all quizzes

class Questions(db.Model):
# table name
__tablename__ = "questions"

id = db.Column(db.Integer, primary_key=True)
quiz_id = db.Column(db.Integer, ForeignKey("quizzes.id"))
text = db.Column(db.String(80))
category = db.Column(db.Integer)
type = db.Column(db.String(80))

Responses:Contains all responses

class Responses(db.Model):
# table name
__tablename__ = "responses"

id = db.Column(db.Integer, primary_key=True)
session_id = db.Column(db.Integer, ForeignKey("sessions.id"))
question_id = db.Column(db.Integer, ForeignKey("questions.id"))
option_id = db.Column(db.Integer, ForeignKey("options.id"))
answer = db.Column(db.String(80), nullable=True)

Responses: When a user starts a quiz, a session is started. This sessions relates to the quiz being played in order to be able to collect the question, and store and relate the responses to a user.

class Sessions(db.Model):
__tablename__ = "sessions"

id = db.Column(db.Integer, primary_key=True)
quiz_id = db.Column(db.Integer, ForeignKey("quizzes.id"))
user_id = db.Column(db.Integer, ForeignKey("users.id"))e here

For the first and third requirement I have written to following code:

question = Questions.query.filter(Questions.quiz_id == quiz.id).order_by(Questions.category).first()

This works in the sense that it returns the questions in te correct order

For the second requirement I have written the following:

    check = Responses.query.filter(Responses.session_id == session[0].id,
                                   Responses.question_id == question.id).scalar() is not None

Next I attempted to create one query, but this was not succesfull. See below code:

question = db.session.query(Questions, Responses).filter(Questions.quiz_id == quiz.id).filter(
        Responses.session_id == session[0].id, Responses.question_id == Questions.id).order_by(Questions.category).scalar() is None
    

The result was it actually only gave me questions which were already answered, instead of unanswered. I am also not sure it's going to filter on the correct question_id already.

EDIT: I think I know have the correct SQL call

SELECT * FROM quiz.questions JOIN quiz.quizzes ON quiz.questions.quiz_id = quiz.quizzes.id WHERE quiz.quizzes.year = 2020 AND quiz.questions.id NOT IN (SELECT question_id FROM quiz.responses WHERE quiz.responses.session_id = 11 ) ORDER BY quiz.questions.category ASC;

Answer 1

You can use except to combine two queries; this will run both queries, and exclude the results of the second query (ie query1 questions - query2 questions):

For example:

# get questions from the current quiz
Questions.query.filter(Questions.quiz_id == quiz.id).\
except(
  # except for questions with a response in the current session 
  Questions.query.filter(
    Questions.quiz_id == quiz.id,
    Questions.id == Responses.question_id,
    Responses.session_id == session[0].id
  )
).order_by(Questions.category).first()

Answer 2

In the end, this was the solution:

        question = Questions.query\
        .filter(Questions.quiz_id == quiz.id) \
        .filter(Responses.session_id == session[0].id) \
        .filter(Responses.question_id != Questions.id) \
        .order_by(Questions.category) \
        .order_by(func.rand()) \
        .first()