awesome-copilot/skills/efcore-d2-db-diagram/references/relationship-rules.md

Relationship Rules

One-to-many

Detected from:

• HasOne(...).WithMany(...)
• FK property on dependent entity.
• Collection navigation on principal entity.

Render dependent to principal:

Orders.ClientId -> Clients.Id: "N:1"

One-to-one

Detected from:

• HasOne(...).WithOne(...)
• Unique FK index.
• Shared primary key relationship.

Render dependent to principal:

ClientProfiles.ClientId -> Clients.Id: "1:1"

Many-to-many

Detected from:

• UsingEntity
• Two collection navigations without explicit join entity.
• Migration-created join table with two FKs and composite key.

Render the join table explicitly by default.

Owned types

Detected from:

• OwnsOne
• OwnsMany
• [Owned]

Inline by default unless table splitting or separate table mapping is detected.

Optional relationships

A relationship is optional when:

• FK is nullable.
• IsRequired(false) is configured.
• Migration column is nullable.

Use dashed line for optional relationships.