feature: id col is used for variable if present

Author: NeedleInAJayStack

src/README.md

@@ -66,7 +66,7 @@ To use them, simply enter the value in the input string. Below is an example of
 ### Query Variables
 
 You can use the Haystack connector to source new variables. Create a query and then enter the name of the column that
-contains the variable values. If no column is specified, the first one is used.
+contains the variable values. If no column is specified, `id` is used if present. Otherwise, the first column is used.
 
 The value injected by the variable exactly matches the displayed value, with the exception of Ref types. Instead, Ref
 types display the "display" portion and inject only the "ID" portion (i.e. `@abc "Site A"` will be displayed as `Site A`

src/datasource.ts

@@ -99,10 +99,14 @@ export class DataSource extends DataSourceWithBackend<HaystackQuery, HaystackDat
     }
 
     return response.data.reduce((acc: MetricFindValue[], frame: DataFrame) => {
+      // Default to the first field
       let field = frame.fields[0];
       if (variableQuery.column !== undefined && variableQuery.column !== '') {
         // If a column was input, match the column name
         field = frame.fields.find((field: Field) => field.name === variableQuery.column) ?? field;
+      } else if (frame.fields.some((field: Field) => field.name === 'id')) {
+        // If there is an id column, use that
+        field = frame.fields.find((field: Field) => field.name === 'id') ?? field;
       }
 
       let fieldVals = field.values.map((value) => {