<graph string="Custom Bar Graph View" type="bar" mode="primary">

doesn't work it results in an error that says
View error context:
-no context-

<graph string="Custom Bar Graph View" type="bar" mode="primary">
<!-- Ensure that only the bar chart is visible -->
<field name="graph_type" invisible="1">bar</field>
<field name="stacked" invisible="1"/>
</graph>

still will not work besides the fact that the mode="primary" is the reason why it said no context
the second reason would be because if you code this in
<field name="graph_type" invisible="1">bar</field>
<field name="stacked" invisible="1"/>
it will say that it is not found in the model