Gallery: ER Diagrams¶
ER and Schema diagrams built with the Chen and SQL table notations.
Entity-Relationship (Chen)¶
er_chen.py
import engrapha_notes as en
import engrapha_diagrams as ed
er = ed.ERDiagram(
width=550, height=260,
caption="Fig 4: University ER"
)
er.entity("STUDENT")
er.entity("COURSE")
er.relationship("ENROLLS")
er.entity_attributes(
"STUDENT",
[("Student_ID", {"pk": True}), "Name", "Email", ("Phone", {"multivalued": True})],
)
er.entity_attributes("COURSE", [("Course_ID", {"pk": True}), "Title", "Credits"])
er.connect("STUDENT", "ENROLLS", card_from="M", card_to="N", total_from=False, total_to=True)
er.connect("COURSE", "ENROLLS", card_from="1", card_to="N")
en.add(er.as_flowable())
Database schema¶
er_schema.py
import engrapha_notes as en
import engrapha_diagrams as ed
schema = ed.SchemaDiagram(
width=530, height=250,
caption="Fig 5: Blog Schema"
)
schema.table("users", [
("id", "INTEGER", {"pk": True}),
("email", "VARCHAR", {}),
("created_at", "TIMESTAMP", {}),
])
schema.table("posts", [
("id", "INTEGER", {"pk": True}),
("user_id", "INTEGER", {"fk": True}),
("title", "VARCHAR", {}),
("published_at", "TIMESTAMP", {}),
])
schema.table("tags", [
("id", "INTEGER", {"pk": True}),
("name", "VARCHAR", {}),
])
schema.relation("posts", "user_id", "users", "id")
schema.relation("tags", "name", "posts", "id")
en.add(schema.as_flowable())
