diff --git a/packages/server/src/api/rest/index.ts b/packages/server/src/api/rest/index.ts
index 36442f4f..32367df4 100644
--- a/packages/server/src/api/rest/index.ts
+++ b/packages/server/src/api/rest/index.ts
@@ -5,6 +5,7 @@ import {
     DbClientContract,
     FieldInfo,
     PrismaErrorCode,
+    clone,
     enumerate,
     getIdFields,
     isPrismaClientKnownRequestError,
@@ -1120,22 +1121,8 @@ class RequestHandler extends APIHandlerBase {
             throw new Error(`serializer not found for model ${model}`);
         }
 
-        const typeInfo = this.typeMap[model];
-
-        let itemsWithId: any = items;
-        if (typeInfo.idFields.length > 1 && Array.isArray(items)) {
-            itemsWithId = items.map((item: any) => {
-                return {
-                    ...item,
-                    [this.makeIdKey(typeInfo.idFields)]: this.makeCompoundId(typeInfo.idFields, item),
-                };
-            });
-        } else if (typeInfo.idFields.length > 1 && typeof items === 'object') {
-            itemsWithId = {
-                ...items,
-                [this.makeIdKey(typeInfo.idFields)]: this.makeCompoundId(typeInfo.idFields, items),
-            };
-        }
+        const itemsWithId = clone(items);
+        this.injectCompoundId(model, itemsWithId);
 
         // serialize to JSON:API structure
         const serialized = await serializer.serialize(itemsWithId, options);
@@ -1154,6 +1141,31 @@ class RequestHandler extends APIHandlerBase {
         return result;
     }
 
+    private injectCompoundId(model: string, items: unknown) {
+        const typeInfo = this.typeMap[lowerCaseFirst(model)];
+        if (!typeInfo) {
+            return;
+        }
+
+        // recursively traverse the entity to create synthetic ID field for models with compound ID
+        enumerate(items).forEach((item: any) => {
+            if (!item) {
+                return;
+            }
+
+            if (typeInfo.idFields.length > 1) {
+                item[this.makeIdKey(typeInfo.idFields)] = this.makeCompoundId(typeInfo.idFields, item);
+            }
+
+            for (const [key, value] of Object.entries(item)) {
+                if (typeInfo.relationships[key]) {
+                    // field is a relationship, recurse
+                    this.injectCompoundId(typeInfo.relationships[key].type, value);
+                }
+            }
+        });
+    }
+
     private toPlainObject(data: any): any {
         if (data === undefined || data === null) {
             return data;
diff --git a/packages/server/tests/api/rest.test.ts b/packages/server/tests/api/rest.test.ts
index f0ba24df..fa7d0cfb 100644
--- a/packages/server/tests/api/rest.test.ts
+++ b/packages/server/tests/api/rest.test.ts
@@ -1373,6 +1373,40 @@ describe('REST server tests', () => {
                             },
                         });
                     });
+
+                    it('get as relationship', async () => {
+                        const r = await handler({
+                            method: 'get',
+                            path: `/post/1`,
+                            query: { include: 'likes' },
+                            prisma,
+                        });
+
+                        expect(r.status).toBe(200);
+                        expect(r.body).toMatchObject({
+                            data: {
+                                relationships: {
+                                    likes: {
+                                        data: [{ type: 'postLike', id: `1${idDivider}user2` }],
+                                    },
+                                },
+                            },
+                            included: [
+                                expect.objectContaining({
+                                    type: 'postLike',
+                                    id: '1_user2',
+                                    attributes: {
+                                        postId: 1,
+                                        userId: 'user2',
+                                        superLike: false,
+                                    },
+                                    links: {
+                                        self: 'http://localhost/api/postLike/1_user2',
+                                    },
+                                }),
+                            ],
+                        });
+                    });
                 });
             });