ClassesExampleInvoices.puml

@startuml (id=invoices)
  class invoices <<entity>> {
    + id : integer {PK} {unique}
    + date :date {required}
    + customer : integer {required}
  }
@enduml

@startuml (id=invoicesDetails)
  class invoicesDetails <<entity>> {
    + id : integer {PK} {unique}
    + product : integer {PK} {unique}
    + quantity :integer {required}
    + price :integer {required}
  }
@enduml

@startuml (id=customers)
  class customers <<entity>> {
    + id :integer {PK} {unique}
    + name :string {required}
  }
@enduml

@startuml (id=products)
  class products <<entity>> {
    + id :integer {PK} {unique}
    + name :string {required}
  }
@enduml

@startuml(id=relations)
!procedure $relations($class1, $class2)
  !if ($class1=="invoices" && $class2=="invoicesDetails") || ($class1=="invoicesDetails" && $class2=="invoices")
    invoices -- invoicesDetails :invoices.id = invoicesDetails.id
  !elseif ($class1=="invoices" && $class2=="customers") || ($class1=="customers" && $class2=="invoices")
    invoices -- customers :invoices.id = customers.id
  !elseif ($class1=="invoicesDetails" && $class2=="products") || ($class1=="products" && $class2=="invoicesDetails")
    invoicesDetails -- products :invoicesDetails.id = products.id
  !endif
!endprocedure
@enduml