From 5ae586ee2cc34d5044492db19f9795b27279628e Mon Sep 17 00:00:00 2001
From: Dmitriy Lazarev <w@kich.dev>
Date: Sat, 16 Dec 2023 01:58:39 +0400
Subject: [PATCH 1/2] Resolve node to null if entity doesn't exist

Signed-off-by: Dmitriy Lazarev <w@kich.dev>
---
 .../src/relationDirectiveMapper.test.ts       | 64 +++++++++++++++++++
 .../src/relationDirectiveMapper.ts            | 22 +++++--
 2 files changed, 80 insertions(+), 6 deletions(-)

diff --git a/plugins/graphql-backend-module-catalog/src/relationDirectiveMapper.test.ts b/plugins/graphql-backend-module-catalog/src/relationDirectiveMapper.test.ts
index 507e3f9b9d..8c38bcfc38 100644
--- a/plugins/graphql-backend-module-catalog/src/relationDirectiveMapper.test.ts
+++ b/plugins/graphql-backend-module-catalog/src/relationDirectiveMapper.test.ts
@@ -563,4 +563,68 @@ describe('mapRelationDirective', () => {
       },
     });
   });
+
+  it('should return null for not existing entities', async () => {
+    const TestModule = createModule({
+      id: 'test',
+      typeDefs: gql`
+        extend interface Node @discriminates(with: "kind")
+
+        type Entity @implements(interface: "Node") {
+          ownedBy: User @relation
+          owner: User @relation(name: "ownedBy")
+          group: Group @relation(name: "ownedBy", kind: "Group")
+        }
+        type User @implements(interface: "Node") {
+          name: String! @field(at: "name")
+        }
+        type Group @implements(interface: "Node") {
+          name: String! @field(at: "name")
+        }
+      `,
+    });
+    const entity = {
+      kind: 'Entity',
+      relations: [
+        { type: 'ownedBy', targetRef: 'user:default/john' },
+        { type: 'ownedBy', targetRef: 'group:default/team-a' },
+      ],
+    };
+    const user = {
+      kind: 'User',
+      name: 'John',
+    };
+    const loader = () =>
+      new DataLoader(async ids =>
+        ids.map(id => {
+          const { query: { ref } = {} } = decodeId(id as string);
+          if (ref === 'user:default/john') return user;
+          if (ref === 'group:default/team-a') return null;
+          return entity;
+        }),
+      );
+    const query = await createGraphQLAPI(TestModule, loader);
+    const result = await query(/* GraphQL */ `
+      node(id: ${JSON.stringify(
+        encodeId({
+          source: 'Mock',
+          typename: 'Entity',
+          query: { ref: 'entity' },
+        }),
+      )}) {
+        ...on Entity {
+          ownedBy { name }
+          owner { name }
+          group { name }
+        }
+      }
+    `);
+    expect(result).toEqual({
+      node: {
+        ownedBy: { name: 'John' },
+        owner: { name: 'John' },
+        group: null,
+      },
+    });
+  });
 });
diff --git a/plugins/graphql-backend-module-catalog/src/relationDirectiveMapper.ts b/plugins/graphql-backend-module-catalog/src/relationDirectiveMapper.ts
index 5114215484..9e3167c10c 100644
--- a/plugins/graphql-backend-module-catalog/src/relationDirectiveMapper.ts
+++ b/plugins/graphql-backend-module-catalog/src/relationDirectiveMapper.ts
@@ -15,7 +15,7 @@ import {
   encodeId,
   isConnectionType,
   createConnectionType,
-  getNodeTypeForConnection
+  getNodeTypeForConnection,
 } from '@frontside/hydraphql';
 import { CATALOG_SOURCE } from './constants';
 
@@ -62,7 +62,7 @@ export function relationDirectiveMapper(
     if (directive.nodeType) {
       const nodeType = getNodeTypeForConnection(
         directive.nodeType,
-        (name) => api.typeMap[name],
+        name => api.typeMap[name],
         (name, type) => (api.typeMap[name] = type),
       );
 
@@ -102,7 +102,7 @@ export function relationDirectiveMapper(
 
     field.resolve = async ({ id }, args, { loader }) => {
       const ids = filterEntityRefs(
-        await loader.load(id) as Entity,
+        (await loader.load(id)) as Entity,
         directive.name,
         directive.kind,
       ).map(ref => ({
@@ -112,15 +112,21 @@ export function relationDirectiveMapper(
           query: { ref },
         }),
       }));
+      const connection = connectionFromArray<{ id: string } | null>(ids, args);
+      (
+        await loader.loadMany(connection.edges.map(({ node }) => node!.id))
+      ).forEach(
+        (entity, index) => !entity && (connection.edges[index].node = null),
+      );
       return {
-        ...connectionFromArray(ids, args),
+        ...connection,
         count: ids.length,
       };
     };
   } else {
     field.resolve = async ({ id }, _, { loader }) => {
-      const ids = filterEntityRefs(
-        await loader.load(id) as Entity,
+      const ids: ({ id: string } | null)[] = filterEntityRefs(
+        (await loader.load(id)) as Entity,
         directive.name,
         directive.kind,
       ).map(ref => ({
@@ -130,6 +136,10 @@ export function relationDirectiveMapper(
           query: { ref },
         }),
       }));
+      if (!isList) ids.splice(1);
+      (await loader.loadMany(ids.map(node => node!.id))).forEach(
+        (entity, index) => !entity && (ids[index] = null),
+      );
       return isList ? ids : ids[0] ?? null;
     };
   }

From d329856fc1f9313571f6019c6d060c56544eeafe Mon Sep 17 00:00:00 2001
From: Dmitriy Lazarev <w@kich.dev>
Date: Mon, 18 Dec 2023 20:47:09 +0400
Subject: [PATCH 2/2] Add changeset

Signed-off-by: Dmitriy Lazarev <w@kich.dev>
---
 .changeset/dry-news-share.md | 5 +++++
 1 file changed, 5 insertions(+)
 create mode 100644 .changeset/dry-news-share.md

diff --git a/.changeset/dry-news-share.md b/.changeset/dry-news-share.md
new file mode 100644
index 0000000000..1a530f582f
--- /dev/null
+++ b/.changeset/dry-news-share.md
@@ -0,0 +1,5 @@
+---
+'@frontside/backstage-plugin-graphql-backend-module-catalog': patch
+---
+
+Resolve node to null if entity doesn't exist