catalog-backend: fix bug where all entities got read back from the catalog

.changeset/early-spies-grow.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-catalog-backend': patch
+---
+
+Fixed a bug where the catalog would read back all entities when adding a location that already exists.

plugins/catalog-backend/src/catalog/DatabaseEntitiesCatalog.ts

@@ -205,7 +205,7 @@ export class DatabaseEntitiesCatalog implements EntitiesCatalog {
         }
       }
 
-      if (options?.outputEntities) {
+      if (options?.outputEntities && responses.length > 0) {
         const writtenEntities = await this.database.entities(
           tx,
           EntityFilters.ofMatchers({
@@ -285,7 +285,8 @@ export class DatabaseEntitiesCatalog implements EntitiesCatalog {
         // instead and call a dedicated batch update database method
         toUpdate.push(request);
       } else {
-        toIgnore.push(request);
+        // Use the existing entity to ensure that we're able to read it back by uid if needed
+        toIgnore.push({ ...request, entity: oldEntity });
       }
     }