Declaring Constraints
As you can see we have declared the first Column as a primary key in the student_table. Running the following command will show the details of the primary key constraint.
Python3
student_table.primary_key |
Output:
PrimaryKeyConstraint(Column(‘id’, Integer(), table=<student_account>, primary_key=True, nullable=False))
A primary key constraint is normally declared implicitly whereas a ForeignKeyConstraint is declared explicitly. We use foreign key constraints if two tables are related to each other by using the object ForeignKey.
Let us create a new Table named address_table which consists of the email address of the student and we will have a foreign key constraint that refers to the student table.
Python3
from sqlalchemy import ForeignKeyaddress_table = Table( "address", metadata_object, Column('id', Integer, primary_key=True), Column('student_id', ForeignKey('student_account.id'), nullable=False), Column('email_address', String, nullable=False) ) |
Describing Databases with MetaData – SQLAlchemy
In this article, we are going to see how to describe Databases with MetaData using SQLAlchemy in Python.
Database Metadata describes the structure of the database in terms of Python data structures. The database usually consists of Tables and Columns. The Database Metadata serves us in generating SQL queries and Object Relational Mapping. It helps us in generating a Schema. The most fundamental objects of Database MetaData are MetaData, Table, and Column.