sqladmin model view for polymorphic models.

[kahngjoonkoh]

I have created a polymorphic data model to ensure data normalization as below.

class Question(Base):
    __tablename__ = "questions"

    id = mapped_column(Integer, primary_key=True, autoincrement=True)
    parent_id = mapped_column(Integer, ForeignKey("questions.id"), nullable=True)
    
    subtopic_id = mapped_column(Integer, ForeignKey("subtopics.id"), nullable=False)
    category = mapped_column(Enum(QuestionCategory), nullable=False)
    type = mapped_column(Enum(QuestionType), nullable=False)
    level = mapped_column(Enum(QuestionDifficulty), nullable=False)
    source = mapped_column(String(250), nullable=True)
    question_text = mapped_column(Text, nullable=False)
    total_mark = mapped_column(Integer, nullable=True) # if null then 0.
    attachment_uri = mapped_column(String(250), nullable=True)

    subquestions = relationship("Question", backref=backref("parent_question", remote_side=[id]), cascade="all, delete-orphan")
    tests = relationship("TestQuestion", back_populates="question")
    user_answers = relationship("UserAnswer", back_populates='question')
    
    __mapper_args__ = {
        'polymorphic_on': type,
        'polymorphic_identity': "question"
    }

    def __repr__(self):
        return f"QuestionID: {self.id}"


class MCQ(Question):
    __tablename__ = 'mcqs'
    
    id = mapped_column(Integer, ForeignKey('questions.id'), primary_key=True, nullable=False)

    option1 = mapped_column(String(250), nullable=False)
    option2 = mapped_column(String(250), nullable=False)
    option3 = mapped_column(String(250), nullable=False)
    option4 = mapped_column(String(250), nullable=False)
    correct_option = mapped_column(Integer, nullable=False)

    correct_explanation = mapped_column(Text, nullable=True)
    incorrect_explanation = mapped_column(Text, nullable=True)
    link = mapped_column(String(250), nullable=True)

    __mapper_args__ = {
        'polymorphic_identity': QuestionType.MCQ,
    }


class ShortAnswerQuestion(Question):
    __tablename__ = "short_answer_questions"

    id = mapped_column(Integer, ForeignKey('questions.id'), primary_key=True, nullable=False)

    is_math = mapped_column(Boolean, nullable=False)
    correct_answer = mapped_column(String(250), nullable=False)
    explanation = mapped_column(Text, nullable=True)
    mark_scheme = mapped_column(Text, nullable=True)

    __mapper_args__ = {
        'polymorphic_identity': QuestionType.SHORT_ANSWER,
    }


class EssayQuestion(Question):
    __tablename__ = "essay_questions"

    id = mapped_column(Integer, ForeignKey('questions.id'), primary_key=True, nullable=False)
    
    mark_scheme = mapped_column(Text, nullable=False)

    __mapper_args__ = {
        'polymorphic_identity': QuestionType.ESSAY,
    }

And to view this on sqladmin modelview, I have implemented the following

class MCQAdmin(ModelView, model=MCQ):
    name = "MCQ"
    category = "Questions"

    column_list = [MCQ.id, MCQ.category, MCQ.level, MCQ.question_text, "subtopic", MCQ.parent_id,  MCQ.correct_option, MCQ.total_mark]
    form_excluded_columns = [MCQ.subquestions, MCQ.tests, MCQ.user_answers]
    column_searchable_list = [MCQ.question_text]
    column_sortable_list = [MCQ.category, MCQ.level, "subtopic"]
    column_formatters = {MCQ.question_text: lambda mcq, a: f"{mcq.question_text[:100]}..." if len(mcq.question_text) > 100 else mcq.question_text}

The following output I get is

  File "C:\Users\User\AppData\Local\Programs\Python\Python312\Lib\site-packages\sqladmin\forms.py", line 163, in _prepare_column
    assert len(prop.columns) == 1, "Multiple-column properties not supported"
           ^^^^^^^^^^^^^^^^^^^^^^

It is possible to view the model and its base model together on the admin panel. However, it does not work when trying to create data for this model.

However, though against common programming practice, I commented out that bit of code assert len(prop.columns) == 1, "Multiple-column properties not supported" and now everything works just as expected.

How significant is this line of code for the rest of the codebase?