Altering Populated Pipelines

Tables can be altered after they have been declared and populated. This is useful when you want to add new secondary attributes or change the data type of existing attributes. Users can use the definition property to update a table's attributes and then use alter to apply the changes in the database. Currently, alter does not support changes to primary key attributes.

Let's say we have a table Student with the following attributes:

@schema
class Student(dj.Manual):
    definition = """
    student_id: int
    ---
    first_name: varchar(40)
    last_name: varchar(40)
    home_address: varchar(100)
    """

We can modify the table to include a new attribute email:

Student.definition = """
student_id: int
---
first_name: varchar(40)
last_name: varchar(40)
home_address: varchar(100)
email: varchar(100)
"""
Student.alter()

The alter method will update the table in the database to include the new attribute email added by the user in the table's definition property.

Similarly, you can modify the data type or length of an existing attribute. For example, to alter the home_address attribute to have a length of 200 characters:

Student.definition = """
student_id: int
---
first_name: varchar(40)
last_name: varchar(40)
home_address: varchar(200)
email: varchar(100)
"""
Student.alter()