django-schema-lens 0.1.0

Full visibility into your Django database schema — diffs, snapshots, audits and more.

django-schema-lens

Full visibility into your Django database schema — diffs, snapshots, audits and more.

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The Problem

Django migrations keep your database in sync, but they tell you nothing about what actually changed, whether a migration is safe to run in production, or what your full schema looks like right now. As a project grows, answering these questions requires reading raw migration Python, querying information_schema, or hoping your documentation is up to date.

django-schema-lens solves this by giving you a suite of manage.py commands that turn your migrations and model registry into human-readable markdown — instantly, with zero setup.

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Features

• Migration diff — compare any two migrations and see exactly what changed per model
• Full schema snapshot — export every model, every field, every constraint to a single markdown file
• Model summary — one clean table listing all registered models with their fields and types
• Breaking change detector — scan all migrations and flag ERROR and WARN level dangerous operations before they reach production
• Migration history log — a full chronological changelog of every migration across all apps
• Zero runtime dependencies — only Django and the Python standard library
• --output flag — save any report to a file
• --app flag — filter any command to a single Django app

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Installation

pip install django-schema-lens

Add to INSTALLED_APPS in your Django settings:

INSTALLED_APPS = [
    ...
    "django_schema_lens",
]

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Quick Start

# See what changed in the last migration
python manage.py schema_lens diff

# Export your full schema to a markdown file
python manage.py schema_lens snapshot --output schema.md

# List all models
python manage.py schema_lens models

# Check for breaking changes before deploying
python manage.py schema_lens audit

# View migration history
python manage.py schema_lens history

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CLI Reference

All commands support --output FILE, --app APP, and --format markdown.

schema_lens diff

Compare the last two migrations (auto-detected), or specify two migration identifiers:

python manage.py schema_lens diff
python manage.py schema_lens diff 0002 0003
python manage.py schema_lens diff --app blog
python manage.py schema_lens diff --output diff.md

Example output:

# Migration Diff

## App: `blog`

**From:** `0001_initial`  →  **To:** `0002_add_published_at`

**Operations:** 2

| Operation   | Model   | Field / Detail              |
| ----------- | ------- | --------------------------- |
| AddField    | post    | published_at                |
| AlterField  | post    | title → CharField (not null)|

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schema_lens snapshot

Export the full current database schema for all installed apps:

python manage.py schema_lens snapshot
python manage.py schema_lens snapshot --output schema.md
python manage.py schema_lens snapshot --app auth

Example output:

# Schema Snapshot

**Apps:** 3  |  **Models:** 7

## App: `auth`

Python module: `django.contrib.auth`  |  Models: 3

### User

DB table: `auth_user`

| Field        | Type        | PK  | Null | Blank | Unique | Default | DB Column    |
| ------------ | ----------- | --- | ---- | ----- | ------ | ------- | ------------ |
| id           | AutoField   | Yes | No   | No    | Yes    | —       | id           |
| username     | CharField   | No  | No   | No    | Yes    | —       | username     |
| email        | CharField   | No  | No   | Yes   | No     | —       | email        |
| is_active    | BooleanField| No  | No   | No    | No     | True    | is_active    |
| date_joined  | DateTimeField| No | No  | No    | No     | now()   | date_joined  |

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schema_lens models

List every registered model across all apps in a compact table:

python manage.py schema_lens models
python manage.py schema_lens models --app myapp
python manage.py schema_lens models --output models.md

Example output:

# Model Summary

**Apps:** 2  |  **Models:** 5

| App    | Model       | DB Table       | Fields | Field Names                         |
| ------ | ----------- | -------------- | ------ | ----------------------------------- |
| auth   | User        | auth_user      | 11     | id, password, last_login, ...       |
| auth   | Group       | auth_group     | 2      | id, name                            |
| blog   | Post        | blog_post      | 5      | id, title, body, author, created_at |
| blog   | Comment     | blog_comment   | 4      | id, post, author, body              |

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schema_lens audit

Detect breaking changes in your migrations. Exits with code 1 if any ERROR-level issues are found — safe to use in CI:

python manage.py schema_lens audit
python manage.py schema_lens audit --app blog
python manage.py schema_lens audit --output audit.md

Example output:

# Breaking Change Audit

**Errors:** 1  |  **Warnings:** 2  |  **Total:** 3

> **1 ERROR(s) found** — these changes may cause data loss or migration failures.

| Severity | App  | Migration              | Operation   | Model | Field / Detail | Message                                         |
| -------- | ---- | ---------------------- | ----------- | ----- | -------------- | ----------------------------------------------- |
| ERROR    | blog | 0005_remove_body       | RemoveField | post  | body           | RemoveField 'body' — column will be dropped.    |
| WARN     | blog | 0006_rename_slug       | RenameField | post  | slug → new_slug| RenameField — code referencing old name breaks. |
| WARN     | blog | 0007_alter_unique      | AlterUniqueTogether | post | —       | Unique constraint removed.                      |

Severity levels:

Severity	Operations
ERROR	RemoveField, DeleteModel, AlterField on a non-null field
WARN	RenameField, RenameModel, AlterUniqueTogether removing constraints, RemoveIndex, RemoveConstraint

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schema_lens history

List all migrations chronologically across every app:

python manage.py schema_lens history
python manage.py schema_lens history --app blog
python manage.py schema_lens history --output history.md

Example output:

# Migration History

**Total migrations:** 6

| #    | App  | Migration                  | Operations | Operation Types        | Dependencies           |
| ---- | ---- | -------------------------- | ---------- | ---------------------- | ---------------------- |
| 0001 | auth | 0001_initial               | 3          | CreateModel, ...       | —                      |
| 0001 | blog | 0001_initial               | 1          | CreateModel            | auth.0001_initial      |
| 0002 | blog | 0002_add_published_at      | 1          | AddField               | blog.0001_initial      |
| 0003 | blog | 0003_alter_title           | 1          | AlterField             | blog.0002_add_...      |

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ERD Generation

Generate a visual Entity Relationship Diagram directly from your Django models — no configuration needed.

Mermaid ERD (renders on GitHub)

python manage.py schema_lens erd --output erd.md
python manage.py schema_lens erd --app blog --output blog_erd.md

The generated .md file renders automatically on GitHub:

erDiagram
    Post {
        AutoField id PK
        CharField title
        TextField content
        BooleanField published
        ForeignKey author FK
    }
    Author {
        AutoField id PK
        CharField name
        EmailField email
    }
    Post }o--|| Author : author

Relationship notation:

Symbol	Relationship
}o--||	ForeignKey (many-to-one)
||--||	OneToOneField (one-to-one)
}o--o{	ManyToManyField (many-to-many)

Field suffixes: PK — primary key · FK — foreign key · UK — unique

Interactive HTML ERD

python manage.py schema_lens erd --format html --output erd.html

Opens in any browser — no server required. Features:

• Dark-themed canvas with a card per model showing all fields and type badges
• Bezier relationship lines (solid for FK/O2O, dashed for M2M) with arrowheads
• Drag cards to rearrange the layout
• Drag background to pan the canvas
• Scroll to zoom in and out
• Click a model card to highlight its relationships
• Hover a line to see a tooltip with the field name and relation type
• Reset Layout button to restore the default grid

Filter by app

# Mermaid, filtered to a single app
python manage.py schema_lens erd --app blog

# Interactive HTML, filtered and saved to file
python manage.py schema_lens erd --app blog --format html --output blog.html

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Comparison with Similar Tools

Feature	django-schema-lens	inspectdb	sqlmigrate	showmigrations
Markdown output	Yes	No	No	No
Migration diff	Yes	No	No	No
Breaking change detection	Yes	No	No	No
Full schema snapshot	Yes	Partial	No	No
Model summary	Yes	No	No	No
Migration history	Yes	No	No	Partial
Zero dependencies	Yes	Yes	Yes	Yes
CI-friendly exit codes	Yes	No	No	No

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Contributing

Contributions are welcome! Please read CONTRIBUTING.md before opening a pull request.

git clone https://github.com/wikidjango/django-schema-lens.git
cd django-schema-lens
python -m venv .venv && source .venv/bin/activate
pip install -e ".[dev]"
pytest django_schema_lens/tests/test_all.py -v

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Disclaimer

This project is not affiliated with, endorsed by, or sponsored by the Django Software Foundation or the Django project. Django is a registered trademark of the Django Software Foundation.

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License

MIT License — see LICENSE for full text.

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