Relationships & ER Diagram API

Complete API reference for Relationship and ErDiagram.

Relationship

Custom (non-ORM) relationship declaration.

from sqlmodel_nexus import Relationship

class Task(SQLModel, table=True):
    __relationships__ = [
        Relationship(
            fk="id",
            target=list[Tag],
            name="tags",
            loader=tags_loader,
        )
    ]

Parameters

Parameter	Type	Required	Description
`fk`	`str`	Yes	Field name on the source entity used by DataLoader to collect key values
`target`	`type`	Yes	Target type (`Entity` or `list[Entity]`)
`name`	`str`	Yes	Relationship name, used for implicit auto-loading matching
`loader`	`type` or `callable`	Yes	DataLoader class or async batch function

Declaration Location

Declare in the __relationships__ class attribute of a SQLModel entity class, as a list of Relationship instances.

target Syntax

# Single target (MANYTOONE)
Relationship(fk="owner_id", target=User, name="owner", loader=user_loader)

# List target (ONETOMANY)
Relationship(fk="id", target=list[Tag], name="tags", loader=tags_loader)

ErDiagram

Mermaid ER diagram generation.

from sqlmodel_nexus import ErDiagram

diagram = ErDiagram(entities=[Sprint, Task, User])

Methods

Method	Signature	Description
`get_diagram()`	`-> str`	Generate a Mermaid ER diagram string
`get_all_entities()`	`-> list`	Get all registered entities
`get_all_relationships()`	`-> list`	Get all registered relationships

Mermaid Output Example

erDiagram
    Sprint ||--o{ Task : "has many"
    Task }o--|| User : "owner"

From ErManager

er = ErManager(base=SQLModel, session_factory=async_session)
diagram = er.get_diagram()
print(diagram.get_diagram())