Positioning of nodes relative to edges in tikz

Question

Earlier I asked a question about labelling the edges of graphs with arrows. Zarko presented a solution that, stripped down to its minimum, looks like this:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{positioning}
\usepackage{mathtools}
\begin{document}
\begin{tikzpicture}
\node (A) at (0,0) {A};
\node (B) at (1,1.5) {B};
\draw (B) --  node[sloped,above] {$\xleftarrow{2}$}  (A);
\end{tikzpicture}
\end{document}

Here is the result:

It looks great in the context of what I'm doing, but I don't like the way the number is slanted - I'd like it to be positioned where it is, but to be upright, like this:

I thought I could do this by defining a second node with a greater outer sep and without the sloped modifier, like this:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{positioning}
\begin{document}
\begin{tikzpicture}
\node (A) at (0,0) {A};
\node (B) at (1,1.5) {B};
\draw (B) --  node[sloped,above] {$\leftarrow$} node[above,outer sep=6pt] {\scriptsize{2}}  (A);
\end{tikzpicture}
\end{document}

However, as you can see this doesn't put the number where I want it, since it's literally above the midpoint of the line, rather than "above" relative to its slope:

Is there a way that I can position the node in the same way as if it was sloped (i.e. by moving a set distance along a line perpendicular to the edge), without the node's contents being sloped? Or is there some other way to achieve the effect I'm after?

Answer 1

You could use an empty sloped node to get the correct position and then use that node's center anchor to place a the desired un-sloped node.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{positioning}
\begin{document}
\begin{tikzpicture}
\node (A) at (0,0) {A};
\node (B) at (1,1.5) {B};
\draw (B) --  node[sloped,above] {$\leftarrow$} node[sloped,above,outer sep=9pt] (x) {} (A);
\node at (x) {\scriptsize{2}};
\end{tikzpicture}
\end{document}

However, the placement doesn't look quite right, so you probably need to manually shift the node position a bit.

Answer 2

Well, my second solution in answer to which you provide link, can be refined as follows:

I changes the size and tip of arrows in pic as well their distance from path to which are added, and add default values for most common pic type. For this solution the TikZ library arrows.meta is not necessary anymore.

\documentclass[tikz,border=3mm]{standalone}
    \usetikzlibrary{chains,positioning}

\begin{document}
\begin{tikzpicture}[
    start chain = A going right,
pics/AB/.style args = {#1/#2/#3}{code={
    \draw[solid,thin,->]
        (-2mm,#1 1.5mm) -- node [#2,font=\footnotesize,inner sep=1pt] {#3} ++ (4mm,0mm);}
                            },
pics/AB/.default=/left/1,
pics/BA/.style args = {#1/#2/#3}{code={
    \draw[solid,thin,<-]
        (-2mm,#1 1.5mm) -- node [#2,font=\footnotesize,inner sep=1pt] {#3} ++ (4mm,0mm);}
                            },
                    ]
    \begin{scope}[every node/.style={circle, draw, minimum size=1.5em,
                                     inner sep=2pt, on chain}]
\foreach \i in {1,...,5} \node {};
%
\node (B-1) [below=of A-2] {A};
\node (B-2) [below=of A-4] {B};
    \end{scope}
    \begin{scope}[sloped]
\draw[densely dotted, thick]
                (A-1) -- (A-2)
                (A-2) -- pic {BA=/above/1} (A-3)
                (A-3) -- (A-4)
                (A-4) -- pic {AB=/above/1} (A-5);
\draw[thick]    (B-1) -- pic {AB} (A-2)
                (B-1) -- pic {AB=-/below right/1} (A-3)
%
                (B-2) -- pic {BA=-/below left/1} (A-3)
                (B-2) -- pic {AB} (A-4)
                ;
%
\draw[double]   (A-1) --  (B-1)
                (A-5) -- pic {BA=-/below right/2} (B-2);
    \end{scope}
\end{tikzpicture}
\end{document}

Answer 3

The coordinate of the new node are relative to the main arrow, not relative to the node. So, one way to do it would be to apply a shift to the new node:

Code:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{positioning}
\begin{document}
\begin{tikzpicture}
\node (A) at (0,0) {A};
\node (B) at (1,1.5) {B};
\draw (B) --  node[sloped,above] {$\leftarrow$} node[shift={(-0.8em,2.1ex)}] {\scriptsize{2}}  (A);
\end{tikzpicture}
\end{document}