A database schema is a model of the information an application must preserve. Before creating Django models, identify the records, their relationships, and the rules that must remain true even when a request contains invalid data.
Choose entities and relationships
For a project tracker, a project can have many tasks, while each task belongs to one project. Relational tables represent these entities; a foreign key connects a task to its project. Decide which values are required, which must be unique, and which relationships may be empty.
Use constraints as a second line of defense
Application validation gives people helpful messages, while database constraints protect stored data if another code path misses a rule. Primary keys, foreign keys, uniqueness, and appropriate nullability all express important parts of the domain. Transactions group related writes so they succeed or fail together.
Read the SQL behind the ORM
Django's ORM provides a Python interface to common queries, but developers still need to reason about joins and result shape. A query that loads related records may create extra database work if relationships are not selected or prefetched intentionally. Inspect generated SQL when a query behaves unexpectedly.
SELECT project.name, COUNT(task.id) AS task_count
FROM projects AS project
LEFT JOIN tasks AS task ON task.project_id = project.id
GROUP BY project.id, project.name;Keep schema changes in reviewed migrations. Migrations describe how the database evolves; do not replace them with a rebuild or data wipe to fix an environment mismatch.