Generating ERD from sqlalchemy#

This posts tests some popular Python tools (sqlalchemy_data_model_visualizer , sqlalchemy_schemadisplay, and eralchemy2) to generate ERD (Entity-Relation Diagram) from sqlalchemy models.

The test code can be found in this Github repo.

Comparison#

Tool name	sqlalchemy_data_model_visualizer	sqlalchemy_schemadisplay	eralchemy2
output format	✅ svg	❌png	✅pdf, png, svg, markdown mermaid
source format	sqlalchemy	sqlalchemy + real DB	✅real DB
column type	✅provided in new column	❌missing (see output png)	provided along with column name
many to many association table	❌missing link (see output svg)	provided	provided
usage	❌should list all the sqlalchemy tables one by one	easy	easy

😊 sqlalchemy_data_model_visualizer has a beautiful SVG output, but missing link for many-to-many association table.
😅 sqlalchemy_schemadisplay has a poor PNG output, and misses column type.
😍 eralchemy2 the output is not as beautiful as sqlalchemy_data_model_visualizer, but the big advantage is that it can generate ERD from database only which is independent from sqlalchemy code, and it supports multiple output formats including Mermaid which can be easily rendered in Markdown.

There's no perfect tool, or I haven't found it yet...

generating ERD from sql code

For a more general approach out of sqlalchemy, you can generate ERD from SQL code using draw.io.

generating sql models from DB

You can generate sqlalchemy models from DB using sqlacodegen.