How can I access columns.roles in Power BI development?

Question

Could not find this answer online, so decided to post the question then the answer.

I created a table in the capabilities.json file:

"dataRoles": [
    {
        "displayName": "Stakeholders",
        "name": "roleIwant",
        "kind": "GroupingOrMeasure"
    }
...
"dataViewMappings": [        
    {
        "table": {
            "rows": {
                "select": [
                    {
                    "for": {
                        "in": "roleIwant"
                    }
                    }
                ]
            }
        }
    }
]

I realized that I could not simply set, for instance, legend data from the first category, because the first category comes from the first piece of data the user drags in, regardless of position. So if they set a bunch of different pieces of data in Power BI online, for instance, then remove one, the orders of everything get messed up. I thought the best way to settle this would be to identify the role of each column and go from there.

When you click on show Dataview, the hierarchy clearly shows:

...table->columns[0]->roles: { "roleIwant": true }

So I thought I could access it like:

...table.columns[0].roles.roleIwant

but that is not the case. I was compiling using pbiviz start from the command prompt, which gives me an error:

error  TYPESCRIPT  /src/visual.ts : (56,50) Property 'roleIwant' does not exist on type '{ [name: string]: boolean; }'.

Why can I not access this in this way? I was thinking because natively, roles does not contain the property roleIwant, which is true, but that shouldn't matter...

Answer 1

The solution is actually pretty simple. I got no 'dot' help (typing a dot after roles for suggestions), but you can use regular object properties for roles. The command for this case would be:

...table.columns[0].roles.hasOwnProperty("roleIwant")

And the functional code portion:

...
columns.forEach((column) =>{
      if(column.roles.hasOwnProperty("roleIwant")){
           roleIwantData = dataview.categorical.categories[columns.indexOf(column)].values;
      })

If it has the property, it belongs to that role. From here, the data saved will contain the actual values of that role! The only thing I would add on here is that if a column is used for multiple roles, depending on how you code, you may want to do multiple if's to check for the different roles belonging to a column instead of if else's.

If anyone has any further advice on the topic, or a better way to do it, by all means. I searched for the error, all over for ways to access columns' roles, and got nothing, so hopefully this topic helps someone else. And sorry for the wordiness - I tend to talk a lot.