How to JOIN three tables with Django ORM

To join three tables using Django ORM, you can follow these steps:

  1. Define the models for the three tables: Create three model classes representing the tables you want to join. Each model should have the necessary fields and relationships defined.

  2. Use the ForeignKey field: In one of the models, add a ForeignKey field for each of the other two models. This establishes the relationship between the tables.

  3. Use the related_name attribute: In each ForeignKey field, specify a related_name attribute. This allows you to access the related objects from the other models.

  4. Use the select_related() method: When querying the main model, use the select_related() method to fetch the related objects in a single query. This reduces the number of database queries and improves performance.

  5. Use the double underscore notation: To access fields from the related models, use the double underscore notation in the query. For example, if you have a ForeignKey field named author in your main model, and you want to access a field named name in the related model, you can use author__name in the query.

Here's an example code snippet that demonstrates these steps:

class Table1(models.Model):
    # Fields for Table1

class Table2(models.Model):
    table1 = models.ForeignKey(Table1, related_name='table2')
    # Fields for Table2

class Table3(models.Model):
    table1 = models.ForeignKey(Table1, related_name='table3')
    # Fields for Table3

# Querying the main model
main_objects = Table1.objects.select_related('table2', 'table3').filter(<filter_conditions>)

# Accessing fields from related models
for main_object in main_objects:
    table2_name = main_object.table2.name
    table3_name = main_object.table3.name

In the above example, we have three tables: Table1, Table2, and Table3. Table2 and Table3 have foreign key relationships with Table1. By using the related_name attribute, we can access the related objects from Table1 as table2 and table3. We can then use the double underscore notation to access fields from the related models in the query.

Note: Make sure to replace <filter_conditions> with the appropriate filter conditions based on your requirements.