bug: Arrow directions reverse when there is a cycle between three or more nodes

[arihantsurana]

Using version 0.19.1 when there are cycles within a diagram, the edge arrow direction seems to reverse.

to reproduce:

from diagrams.onprem.database import PostgreSQL
from diagrams import Diagram
with Diagram("check", show=False, direction="LR", curvestyle="curved"):
  a = PostgreSQL("A")
  b = PostgreSQL("B")
  c = PostgreSQL("C")
  d = PostgreSQL("D")
  a >> b >> c
  b >> d >> a

Output:

the arrow from d to a is reversed.

[clayms]

Likely related to issue https://github.com/mingrammer/diagrams/issues/367 , as you can see in the output below when I run your code in a notebook.

This does not address the bug you reported, but see if the following work-around will help.

from diagrams.onprem.database import PostgreSQL
from diagrams import Diagram

graph_attr = {
    "splines":"spline",
}

with Diagram("check", show=False, graph_attr=graph_attr) as diag:
    a = PostgreSQL("A")
    b = PostgreSQL("B")
    c = PostgreSQL("C")
    d = PostgreSQL("D")
    a >> b >> c
    b >> d >> a

diag

See graphviz splines docs for more info.

[clayms]

I think it may be related to the headclip and tailclip Edge attributes.

from diagrams.onprem.database import PostgreSQL
from diagrams import Diagram, Edge

graph_attr = {
    "splines":"curved",
}

with Diagram("check", show=False, graph_attr=graph_attr) as diag:
    a = PostgreSQL("A")
    b = PostgreSQL("B")
    c = PostgreSQL("C")
    d = PostgreSQL("D")
    a >> Edge(headclip="a", tailclip="a") >> b >> Edge(headclip="b", tailclip="b") >> c
    b >> Edge(headclip="c", tailclip="c") >> d >> Edge(headclip="d", tailclip="d") >> a

diag

[clayms]

looks like an underlying issue with Graphviz:

https://github.com/mdaines/viz.js/issues/29#issuecomment-41865753

[clayms]

Perhaps Stephen North, Graphviz Developer (github) knows. see this post on the Graphviz forums.

[arihantsurana]

from diagrams.onprem.database import PostgreSQL
from diagrams import Diagram

graph_attr = {
    "splines":"spline",
}

with Diagram("check", show=False, graph_attr=graph_attr) as diag:
    a = PostgreSQL("A")
    b = PostgreSQL("B")
    c = PostgreSQL("C")
    d = PostgreSQL("D")
    a >> b >> c
    b >> d >> a

diag

This workaround works for me!

[clayms]

@arihantsurana are you being facetious, or does it actually plot correctly for you? I can't imagine that you want the double arrows. Also, one of the arrows from D to A is still reversed.

The second plot in this comment is closer to what you want, no?

[arihantsurana]

@arihantsurana are you being facetious, or does it actually plot correctly for you? I can't imagine that you want the double arrows. Also, one of the arrows from D to A is still reversed.

The second plot in this comment is closer to what you want, no?

Apologies. I must have incorrectly quote replied. You are correct, the second plot is what works. Updated my comment.