Ensure that emitted relations are deduplicated

Signed-off-by: Fredrik Adelöw <freben@gmail.com>

.changeset/swift-fishes-taste.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-catalog-backend': patch
+---
+
+Ensure that emitted relations are deduplicated

.github/styles/vocab.txt

@@ -57,6 +57,7 @@ deadnaming
 debounce
 Debounce
 declaratively
+deduplicated
 deps
 destructured
 dev

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']));

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!,