如何使用django通过选定的字段(不是整型而是字符串)连接两个已有的表？

from django.db import models

class Table1(models.Model):
    common_field = models.CharField(max_length=100)
    # 其他字段...

class Table2(models.Model):
    common_field = models.CharField(max_length=100)
    # 其他字段...

class ConnectedTable(models.Model):
    selected_field = models.CharField(max_length=100)
    table1 = models.ForeignKey(Table1, on_delete=models.CASCADE)
    table2 = models.ForeignKey(Table2, on_delete=models.CASCADE)

python manage.py makemigrations
python manage.py migrate

selected_value = "example_value"
table1_instance = Table1.objects.get(common_field=selected_value)
table2_instance = Table2.objects.get(common_field=selected_value)

connected_table = ConnectedTable(selected_field=selected_value, table1=table1_instance, table2=table2_instance)
connected_table.save()