This feature is under development, but we fixed several issue in the last beta. We also enhanced it so that you can use in your case.
With this beta: https://dl.dropboxusercontent.com/u/13064071/plantuml.jar
Now, the following diagram is working:
@startuml
hide empty methods
hide circle
'skinparam linetype ortho
!define PK <size:12><&key></size><b>
!define FK <size:12><&link-intact></size><i>
!define PP <size:12><&caret-right></size>
class "<b> Some dict </b>" as d {
PK ID \t\t Integer
PP Name \t String
}
class "<b> Some entity </b>" as e {
PK ID \t\t Integer
FK Type \t\t Integer
PP Some field \t JSON
}
e::Type }-- d::ID
@enduml
Unfortunately, the skinparam linetype ortho does not work very well, and there is nothing we can really do here (all this is managed by Graphviz/Dot).
Well, there may be one solution: we could still request Graphviz/Dot to do B-splines, and then we could transform those B-splines into segment for the drawing.
Not sure that it will give some good drawing. And it needs some work.
Another thing that we can do is to enhance crowfoot drawing to only handle 0/90/180/270 angle (should be easy to do).
Does it sound good to you?