ERDIG — Declarative ER Schemas & Diagrams (Python)

ERDIG is a tiny, dependency-free Python library for declaring Entity–Relationship (ER) models in code and generating ER diagrams. It provides a Pythonic DSL to define entities, attributes, relationships (including n-ary and relationship attributes), cardinalities, domains/enums, and generalization (inheritance). Models validate to a canonical, renderer-agnostic IR which can be rendered to Graphviz DOT/SVG/PNG/PDF. An optional SQLite helper can generate DDL and initialize a database file from your model.

• No non-stdlib dependencies
• Strong validation with helpful error messages
• Stable, deterministic IR via Schema.to_spec()
• Graphviz renderer included (uses your system dot if present)
• Optional SQLite DDL generator + executor (pure stdlib)

Installation

No installation is required if you use this repository directly. The package is pure Python and has no external dependencies.

• Optional: install Graphviz to export SVG/PNG/PDF. On most systems installing Graphviz adds the dot command to your PATH.
• Optional: install pandoc to enable Markdown-to-PDF export (erdig.markdown.MarkdownAssembler.save_pdf).
• Without Graphviz, you can still save .dot/.gv files and view them with any DOT viewer.

Quick Example

from erdig import Schema, T, Role, one, zero_or_more

s = Schema("Blog")
User = (
    s.entity("User").attr("id", T.UUID, nullable=False).attr("email", T.String(120)).pk("id").unique("email")
)
Post = s.entity("Post").attr("id", T.BigInt, nullable=False).attr("title", T.String(200), nullable=False).pk("id")

s.relationship("Writes", Role(User, one()), Role(Post, zero_or_more()))

s.validate()
diagram = s.diagram()
diagram.save("blog.dot")    # always available
# diagram.save("blog.svg")  # requires Graphviz

Project Structure

• erdig/ ... library implementation
• examples/ ... runnable examples (small/medium/big)
• docs/ ... documentation

Documentation Map

• Quick start: docs/quickstart.md
• Public API: docs/api.md
• SQLite DDL: docs/sqlite.md
• Markdown docs: docs/markdown.md
• Modeling cookbook: docs/modeling-cookbook.md
• IR format: docs/ir.md
• Rendering: docs/rendering.md
• Validation & errors: docs/validation.md

License

MIT License