Many to many but custom "through table"?

[DusanKovacevic94]

I want use a model to define a custom "through table" for my models, but I couldn't find an example for it, please help.

[Abdeldjalil-H]

To use a custom "through table" for many-to-many relationships in Tortoise ORM, you can follow this example that shows a Student-Course relationship with grades:

from tortoise import fields, models, Tortoise


class Student(models.Model):
    id = fields.IntField(pk=True)
    name = fields.CharField(max_length=100)
    email = fields.CharField(max_length=255)
    created_at = fields.DatetimeField(auto_now_add=True)

    # The key part is setting up the ManyToManyField with a through model
    courses = fields.ManyToManyField(
        "models.Course",                # Target model
        through="models.StudentCourse", # Your custom through model
        forward_key="course_id",        # Foreign key in through model pointing to Course
        backward_key="student_id",      # Foreign key in through model pointing to Student
        related_name="students",        # Name to use when accessing from Course model
    )


class Course(models.Model):
    id = fields.IntField(pk=True)
    title = fields.CharField(max_length=200)
    description = fields.TextField()
    created_at = fields.DatetimeField(auto_now_add=True)


class StudentCourse(models.Model):
    id = fields.IntField(pk=True)
    # These foreign keys must match the forward_key and backward_key names above
    student = fields.ForeignKeyField("models.Student", related_name="student_courses")
    course = fields.ForeignKeyField("models.Course", related_name="student_courses")
    # Add any additional fields you need in the through table
    grade = fields.CharField(max_length=2, null=True)

    class Meta:
        # Prevents duplicate enrollments
        unique_together = (("student", "course"),)

So in simpler terms:

• through is your custom table that stores the relationship
• forward_key points to where you're going
• backward_key points to where you came from

[henadzit]

We definitely want to support this in a more convenient way. Here's a related issue.

[DusanKovacevic94]

Thanks, I was missing these forward_key backward_key arguments, so it was giving me errors when trying to add.

Thanks a bunch!

[Abdeldjalil-H]

@DusanKovacevic94 can you mark it as answer please.

[Abdeldjalil-H]

@henadzit. Maybe I am missing something, but the code I provided works correctly. Maybe we need to document this.

[henadzit]

That would be great!