I’m updating an app from 1.5 to 1.7 and changing to components/heex, and it’s led me to a question about what the Right Way™ to do something is… Here is the current state of things:

I have a component that generates SVG code representing a gauge. Think speedometer 0-60 kinda thing. This object is updated every 15 seconds with fresh data and redraws.

Currently the way I have things organized to have a module in AppWeb/views/gauge_arc.ex, which contains a struct, a type, and helper functions, including a “build_from_values()” function which takes the numerical values, and populates the remaining fields of the struct with values like “svg_bg_path_string” and “svg_fill_path_string” and “main_label_text”.

In my LiveView I fetch the data, create a new %GaugeArc{} with the basic values, pass that to GaugeArc.build_from_values() to fill in the computed values, and store the entire %GaugeArc{} into the assigns in a variable indicating what the gauge represents. (my page has several GaugeArcs on it)
The LiveView then calls a LiveComponent for each arc, passing in the correct struct from assigns, and the component pulls out the values it needs from the computed fields via @gaugeArc.svg_bg_path_string and the like.

All in all, in phx1.5 land, it’s actually been a pretty reasonable way to move a bunch of data into a liveview, from a code organization perspective.

My questions though:

1. I feel like passing a 30-field struct into @assigns for a component is probably… not recommended? The final LiveComponent only uses 13 of them, 3 of which should never change for the life of the component. My assumption is that the correct way to do this in 1.7 would be to create a component with 13 individual attrs, but this still leaves the problem of how to handle getting that data into the assigns in the LiveView itself. 13 attrs each for 4 or more individual arcs. I could have mount/1 create @arc1_val1, @arc1_val2, … variables, but that seems inelegant. Is that the recommended solution for something like this, or was I on the right track with a custom struct to pass into @assigns?
2. In 1.7 LiveComponent world, where is the preferred place for the code for these sorts of custom structs or helpers? They are firmly display-only, and generate HTML/SVG code, so I felt that they belonged in AppWeb, not over in App, but I’m not quite sure where to put them in the directory structure. Putting the struct/type/functions directly inside the app_web/components/gauge_arc.ex didn’t seem right. A “helpers” directory perhaps? Curious to see what others do for this.

It’s worth noting that this is a very low-impact project, it will never have more than maybe 10 concurrent users, so sacrificing some performance was never a problem. I’m just trying to think through the Right Way™ so that if I ever run into a bigger project with similar needs I’ve got some ideas, and a better understanding of how te work with change tracking rather than against it.