Relationship from Model Data and inheritance #507

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1. Franksign

   added

   questionFurther information is requestedFurther information is requested

   on Nov 23, 2022
2. Kludex commented on Nov 23, 2022

   

   Kludex

   on Nov 23, 2022

   Last edited by Kludex

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   If you can provide an MRE, I can try to help. 👀

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3. phi-friday commented on Nov 23, 2022

   

   phi-friday

   on Nov 23, 2022

   Contributor

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   it works

   from typing import List, Optional, ClassVar
   from sqlmodel import create_engine, Session, SQLModel, Field, Relationship
   
   engine = create_engine('sqlite://',echo=True)
   
   class SurveyDTO(SQLModel):
       ...
       # other fields.. 
   
   class ResponsesDTO(SQLModel):
       code: int
       response: str
   
   class SurveyTable(SurveyDTO, table=True):
       __tablename__: ClassVar[str] = 'survey_table'
   
       id: Optional[int] = Field(default=None, primary_key=True)
       # how to manage relationship from DTO?
       responses: List["ResponsesTable"] = Relationship()
   
   class ResponsesTable(ResponsesDTO, table=True):
       __tablename__: ClassVar[str] = 'responses_table'
   
       id: Optional[int] = Field(default=None, primary_key=True)
       # how to manage relationship from DTO?
       survey_id: Optional[int] = Field(default=None, foreign_key='survey_table.id')
       survey: SurveyTable = Relationship()
   
   def main():
       with Session(engine) as session:
           SQLModel.metadata.create_all(session.connection())
           session.commit()
   
           survey = SurveyTable()
           response1 = ResponsesTable(code=1, response='test1')
           response2 = ResponsesTable(code=1, response='test2')
           response3 = ResponsesTable(code=1, response='test3')
           survey.responses = [response1, response2, response3]
           session.add(survey)
           session.commit()
   
       with Session(engine) as session:
           survey = session.get(SurveyTable, 1)
           print(survey)
           if survey is not None:
               print(survey.responses)
   
   if __name__ == '__main__':
       main()

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4. Franksign commented on Nov 24, 2022

   

   Franksign

   on Nov 24, 2022

   Last edited by Franksign

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   This solves the problem from the SQLModel side. From FastAPI side the SurveyDTO and the list come as JSON payload from a POST request.

   @app.post(endpoint_paths.SURVEY)
   def post_survey(session: Session = Depends(get_session), survey: SurveyDTO= Body(..., `embed=True))
   

   We could say that the object in the POST request should bea a SurveyTable but in this way I am exposing db data to the outside (and to documentation).

   If I define the list in SurveyDTO and ovverride in SurveyTable I get ValueError: The field responses has no matching SQLAlchemy type. Is there a way to map a field from DTO to a table field? Or I need to just duplicate the field in the parent.

   Edit: added the additional context with related PR and issue.

   Thank you guys!

   👍React with 👍2Reacted by Ryan Caught and Snehasish Barman
5. fastapi

   locked and limited conversation to collaborators on Aug 7, 2025
6. YuriiMotov

   converted this issue into a discussion #1464 on Aug 7, 2025