From aa2b15d9dfa4006e547b8bdd95ac4106eba42256 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Fredrik=20Adel=C3=B6w?= <freben@gmail.com>
Date: Mon, 28 Jun 2021 11:49:09 +0200
Subject: [PATCH] Ensure that emitted relations are deduplicated
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Signed-off-by: Fredrik Adelöw <freben@gmail.com>
---
 .changeset/swift-fishes-taste.md                           | 5 +++++
 .github/styles/vocab.txt                                   | 1 +
 .../catalog-backend/src/next/stitching/Stitcher.test.ts    | 7 +++++++
 plugins/catalog-backend/src/next/stitching/Stitcher.ts     | 7 ++++++-
 4 files changed, 19 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/swift-fishes-taste.md

diff --git a/.changeset/swift-fishes-taste.md b/.changeset/swift-fishes-taste.md
new file mode 100644
index 0000000000..8003e67698
--- /dev/null
+++ b/.changeset/swift-fishes-taste.md
@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-catalog-backend': patch
+---
+
+Ensure that emitted relations are deduplicated
diff --git a/.github/styles/vocab.txt b/.github/styles/vocab.txt
index 8b5522b4a3..0fd00e5737 100644
--- a/.github/styles/vocab.txt
+++ b/.github/styles/vocab.txt
@@ -57,6 +57,7 @@ deadnaming
 debounce
 Debounce
 declaratively
+deduplicated
 deps
 destructured
 dev
diff --git a/plugins/catalog-backend/src/next/stitching/Stitcher.test.ts b/plugins/catalog-backend/src/next/stitching/Stitcher.test.ts
index e749fe712d..96af65fffb 100644
--- a/plugins/catalog-backend/src/next/stitching/Stitcher.test.ts
+++ b/plugins/catalog-backend/src/next/stitching/Stitcher.test.ts
@@ -74,6 +74,13 @@ describe('Stitcher', () => {
           type: 'looksAt',
           target_entity_ref: 'k:ns/other',
         },
+        // handles and ignores duplicates
+        {
+          originating_entity_id: 'my-id',
+          source_entity_ref: 'k:ns/n',
+          type: 'looksAt',
+          target_entity_ref: 'k:ns/other',
+        },
       ]);
 
       await stitcher.stitch(new Set(['k:ns/n']));
diff --git a/plugins/catalog-backend/src/next/stitching/Stitcher.ts b/plugins/catalog-backend/src/next/stitching/Stitcher.ts
index bdfa76e5fc..0aa39f5ac8 100644
--- a/plugins/catalog-backend/src/next/stitching/Stitcher.ts
+++ b/plugins/catalog-backend/src/next/stitching/Stitcher.ts
@@ -22,6 +22,7 @@ import {
 } from '@backstage/catalog-model';
 import { SerializedError } from '@backstage/errors';
 import { Knex } from 'knex';
+import { uniqBy } from 'lodash';
 import { v4 as uuid } from 'uuid';
 import { Logger } from 'winston';
 import {
@@ -168,7 +169,11 @@ export class Stitcher {
 
         // TODO: entityRef is lower case and should be uppercase in the final
         // result
-        entity.relations = result
+        const uniqueRelationRows = uniqBy(
+          result,
+          r => `${r.relationType}:${r.relationTarget}`,
+        );
+        entity.relations = uniqueRelationRows
           .filter(row => row.relationType /* exclude null row, if relevant */)
           .map(row => ({
             type: row.relationType!,