From e1af571efdd1433a837a47dc5055e338c3fa0e20 Mon Sep 17 00:00:00 2001
From: Ryan McKinley <ryantxu@gmail.com>
Date: Thu, 3 Jun 2021 16:05:08 -0700
Subject: [PATCH] Timeseries: move join field to index zero (#35217)

---
 .../transformers/joinDataFrames.test.ts           |  4 ++--
 .../transformers/joinDataFrames.ts                | 15 ++++++++++++---
 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/packages/grafana-data/src/transformations/transformers/joinDataFrames.test.ts b/packages/grafana-data/src/transformations/transformers/joinDataFrames.test.ts
index 5f6a5a10018..d1612fdc839 100644
--- a/packages/grafana-data/src/transformations/transformers/joinDataFrames.test.ts
+++ b/packages/grafana-data/src/transformations/transformers/joinDataFrames.test.ts
@@ -180,11 +180,11 @@ describe('align frames', () => {
     `);
   });
 
-  it('sort single frame', () => {
+  it('sort single frame as index zero', () => {
     const series1 = toDataFrame({
       fields: [
-        { name: 'TheTime', type: FieldType.time, values: [6000, 2000, 1500] },
         { name: 'A1', type: FieldType.number, values: [1, 22, 15] },
+        { name: 'TheTime', type: FieldType.time, values: [6000, 2000, 1500] },
       ],
     });
 
diff --git a/packages/grafana-data/src/transformations/transformers/joinDataFrames.ts b/packages/grafana-data/src/transformations/transformers/joinDataFrames.ts
index 6fb8f204618..4288f3690e4 100644
--- a/packages/grafana-data/src/transformations/transformers/joinDataFrames.ts
+++ b/packages/grafana-data/src/transformations/transformers/joinDataFrames.ts
@@ -78,6 +78,9 @@ export function outerJoinDataFrames(options: JoinOptions): DataFrame | undefined
     let frame = options.frames[0];
     let frameCopy = frame;
 
+    const joinFieldMatcher = getJoinMatcher(options);
+    let joinIndex = frameCopy.fields.findIndex((f) => joinFieldMatcher(f, frameCopy, options.frames));
+
     if (options.keepOriginIndices) {
       frameCopy = {
         ...frame,
@@ -95,10 +98,16 @@ export function outerJoinDataFrames(options: JoinOptions): DataFrame | undefined
           return copy;
         }),
       };
-    }
 
-    const joinFieldMatcher = getJoinMatcher(options);
-    const joinIndex = frameCopy.fields.findIndex((f) => joinFieldMatcher(f, frameCopy, options.frames));
+      // Make sure the join field is first
+      if (joinIndex > 0) {
+        const joinField = frameCopy.fields[joinIndex];
+        const fields = frameCopy.fields.filter((f, idx) => idx !== joinIndex);
+        fields.unshift(joinField);
+        frameCopy.fields = fields;
+        joinIndex = 0;
+      }
+    }
 
     if (options.enforceSort) {
       if (joinIndex >= 0) {