ConvertFieldType: Update "join with" to work on array of strings (#105074)

* fix: update join with to work on array of strings

* chore: simplify

* chore: cleanup

* chore: add tests!

* fix: more robust check

packages/grafana-data/src/transformations/transformers/convertFieldType.test.ts

@@ -359,7 +359,7 @@ describe('field convert types transformer', () => {
     ]);
   });
 
-  it('will support custom join separators', () => {
+  it('will support custom join separators for field type other', () => {
     const options = {
       conversions: [{ targetField: 'vals', destinationType: FieldType.string, joinWith: '|' }],
     };
@@ -391,6 +391,38 @@ describe('field convert types transformer', () => {
     ]);
   });
 
+  it('will support custom join separators for field type string', () => {
+    const options = {
+      conversions: [{ targetField: 'string_arrays', destinationType: FieldType.string, joinWith: '&' }],
+    };
+
+    const stringArrayValues = toDataFrame({
+      fields: [
+        {
+          name: 'string_arrays',
+          type: FieldType.string,
+          values: [
+            ['a', 'b', 'c'],
+            ['d', 'e', 'f'],
+          ],
+        },
+      ],
+    });
+
+    const stringified = convertFieldTypes(options, [stringArrayValues]);
+    expect(
+      stringified[0].fields.map(({ type, values }) => ({
+        type,
+        values,
+      }))
+    ).toEqual([
+      {
+        type: FieldType.string,
+        values: ['a&b&c', 'd&e&f'],
+      },
+    ]);
+  });
+
   it('will convert time fields to strings', () => {
     const options = {
       conversions: [{ targetField: 'time', destinationType: FieldType.string, dateFormat: 'YYYY-MM' }],

packages/grafana-data/src/transformations/transformers/convertFieldType.ts

@@ -210,12 +210,15 @@ export function fieldToStringField(
       values = values.map((v) => dateTimeParse(v, parseOptions).format(dateFormat));
       break;
 
+    // Handle both "string" and "other" types to ensure compatibility across Grafana versions (10 & 11)
+    // In some cases fields are classified as 'other' in Grafana 10 but as 'string' in Grafana 11
+    case FieldType.string:
     case FieldType.other:
       values = values.map((v) => {
         if (joinWith?.length && Array.isArray(v)) {
           return v.join(joinWith);
         }
-        return JSON.stringify(v); // will quote strings and avoid "object"
+        return field.type === FieldType.other ? JSON.stringify(v) : `${v}`;
       });
       break;
 

public/app/features/transformers/editors/ConvertFieldTypeTransformerEditor.tsx

@@ -130,6 +130,14 @@ export const ConvertFieldTypeTransformerEditor = ({
     <>
       {options.conversions.map((c: ConvertFieldTypeOptions, idx: number) => {
         const targetField = findField(input?.[0], c.targetField);
+
+        // Show "Join with" input when:
+        // - A join value exists (maintains backward compatibility)
+        // - Target field type is 'other' (Grafana 10) or 'string' (Grafana 11)
+        // This ensures consistent UI across versions where arrays may be classified differently.
+        const shouldRenderJoinWith =
+          c.joinWith?.length || (targetField?.type && [FieldType.other, FieldType.string].includes(targetField.type));
+
         return (
           <div key={`${c.targetField}-${idx}`}>
             <InlineFieldRow>
@@ -169,7 +177,7 @@ export const ConvertFieldTypeTransformerEditor = ({
               )}
               {c.destinationType === FieldType.string && (
                 <>
-                  {(c.joinWith?.length || targetField?.type === FieldType.other) && (
+                  {shouldRenderJoinWith && (
                     <InlineField
                       label={t('transformers.convert-field-type-transformer-editor.label-join-with', 'Join with')}
                       tooltip={t(
@@ -182,7 +190,7 @@ export const ConvertFieldTypeTransformerEditor = ({
                         // eslint-disable-next-line @grafana/no-untranslated-strings
                         placeholder={'JSON'}
                         onChange={onJoinWithChange(idx)}
-                        width={9}
+                        width={16}
                       />
                     </InlineField>
                   )}