Ttdfjt

I've developed a pgfplots ybar chart with white horizontal grid lines over the vertical bars to help the reader judge the length of the bars. The "base" of the ybar chart (the x-axis) is set to y=1 so that I can see whether the normalized results are above or below the axis at y=1. My problem is that I'm having trouble drawing the black x-axis line at y=1 without it being overwritten by a white grid line.

documentclass[border=10pt]standalone
usepackagepgfplots
usepackagepgfplotstable
pgfplotssetcompat=newest

begindocument
pgfplotstableread[col sep=comma,header=false]
 Cat A, 1.06
 Cat B, 0.92
 Cat C, 1.01
 Cat D, 1.04
 Cat E, 0.88
datatable
begintikzpicture
beginaxis[
 ybar, 
 enlarge x limits=0.2,
 height=4cm,
 ymax=0.125,
 ymin=-0.125,
 xticklabels from table=datatable0,
 xtick=data,
 ytick=-0.1,-0.05,...,0.1,
 yticklabels=0.90,0.95,1.00,1.05,1.10,
 ytick pos=left,
 ymajorgrids=true,
 major grid style=thin,color=white, 
 axis on top,
 ylabel=Normalized value,
 x axis line style=draw opacity=0,
 xtick style=draw=none,
 xticklabel style=
 rotate=90, 
 anchor=east,
 
]
 addplot [fill=black,draw=none] table [x expr=coordindex, y expr=thisrowno1-1] datatable;
 draw [black,thin] (rel axis cs:0,0.5) -- (rel axis cs:1,0.5);
endaxis
endtikzpicture
enddocument

If I remove axis on top, the x-axis is drawn correctly, but then I lose the white grid lines over the vertical bars.

How can I change my plot such that the x-axis is drawn last or in such a way that it is drawn on top of the grid line?

You can achieve this by using the set layers feature. Then you simply need to draw the black line on the top most layer ...

% used PGFPlots v1.16
documentclass[border=5pt]standalone
usepackagepgfplots
usepackagepgfplotstable
 pgfplotssetcompat=newest
begindocument
begintikzpicture
 pgfplotstableread[
 col sep=comma,
 header=false,
 ]
 Cat A, 1.06
 Cat B, 0.92
 Cat C, 1.01
 Cat D, 1.04
 Cat E, 0.88
 datatable
 beginaxis[
 set layers, % <-- added
 ybar,
 enlarge x limits=0.2,
 height=4cm,
 ymax=0.125,
 ymin=-0.125,
 xticklabels from table=datatable0,
 xtick=data,
 ytick=-0.1,-0.05,...,0.1,
 yticklabels=0.90,0.95,1.00,1.05,1.10,
 ytick pos=left,
 ymajorgrids=true,
 major grid style=thin,color=white,
 axis on top,
 ylabel=Normalized value,
 x axis line style=draw opacity=0,
 xtick style=draw=none,
 xticklabel style=
 rotate=90,
 anchor=east,
 ,
 ]
 addplot [fill=black,draw=none] table [
 x expr=coordindex,
 y expr=thisrowno1-1,
 ] datatable;

 pgfonlayeraxis foreground
 draw [black,thin] (rel axis cs:0,0.5) -- (rel axis cs:1,0.5);
 endpgfonlayer
 endaxis
endtikzpicture
enddocument

This is somewhat a workaround

documentclass[border=10pt]standalone
usepackagepgfplots
usepackagepgfplotstable
pgfplotssetcompat=newest

begindocument
pgfplotstableread[col sep=comma,header=false]
 Cat A, 1.06
 Cat B, 0.92
 Cat C, 1.01
 Cat D, 1.04
 Cat E, 0.88
datatable
begintikzpicture
beginaxis[
 ybar, 
 enlarge x limits=0.2,
 height=4cm,
 ymax=0.125,
 ymin=-0.125,
 xticklabels from table=datatable0,
 xtick=data,
 ytick=-0.1,-0.05,...,0.1,
 yticklabels=0.90,0.95,1.00,1.05,1.10,
 ytick pos=left,
 ymajorgrids=true,
 major grid style=thin,color=white, 
 axis on top,
 ylabel=Normalized value,
 x axis line style=draw opacity=0,
 xtick style=draw=none,
 xticklabel style=
 rotate=90, 
 anchor=east,
 
]
 addplot [fill=black,draw=none] table [x expr=coordindex, y expr=thisrowno1-1] datatable;
endaxis
draw (rel axis cs:0.2,0.5) -- (rel axis cs:1.1,0.5);
endtikzpicture
enddocument