how can I get data from a table that is liked to a table that is liked to another one it self?

Question

I have three tables,result, course and study, they are like follows

class Study(models.Model):
    id_study = models.IntegerField(primary_key=True)
    study_name = models.CharField(max_length=45)
    description = models.CharField(max_length=45, blank=True, null=True)
    language = models.CharField(max_length=45)
    number_of_years = models.CharField(max_length=45)

class Course(models.Model):
    id_course = models.AutoField(primary_key=True)
    course_name = models.CharField(max_length=45, blank=True, null=True)
    description = models.CharField(max_length=45, blank=True, null=True)
    credits = models.CharField(max_length=45, blank=True, null=True)
    teacher_id_teacher = models.ForeignKey('Teacher', models.DO_NOTHING, db_column='teacher_id_teacher')
    study_id_study = models.ForeignKey('Study', models.DO_NOTHING, db_column='study_id_study')

class Exam(models.Model):
    id_exam = models.AutoField(primary_key=True)
    room = models.CharField(max_length=45, blank=True, null=True)
    resit = models.CharField(max_length=45, blank=True, null=True)
    date = models.DateField(blank=True, null=True)
    time = models.TimeField(blank=True, null=True)
    course_id_course = models.ForeignKey(Course, models.DO_NOTHING, db_column='course_id_course')


class Result(models.Model):
    id_result = models.AutoField(primary_key=True)
    grade = models.IntegerField(blank=True, null=True)
    exam_id_exam = models.ForeignKey(Exam, models.DO_NOTHING, db_column='exam_id_exam')
    date = models.DateField(blank=True, null=True)
    student_id_student = models.ForeignKey('Student', models.DO_NOTHING, db_column='student_id_student')
    passed = models.CharField(max_length=45, blank=True, null=True)

I want to get a result object depending on the study_id I give

Result depends on Exam, Exam depends on Course and Course depends on study

Thanks in advance

Answer 1

You can follow relationships in queries by using the double underscore notation

Result.objects.filter(
    exam_id_exam__course_id_course__study_id_study__id=study_id
)

For what it's worth: you have an odd naming convention for your foreign keys, usually a foreign key to a model named Exam would be named exam , you are already setting db_column for each foreign key so you don't need to name them this way. If you changed their names to be the model name lowercase it would look like this which is probably more readable

Result.objects.filter(exam__course__study__id=study_id)