fix: return 404 when a model was not found

Modify repository method `findById` to set `code = 'MODEL_NOT_FOUND'`
on the error thrown when no model instance was found.

Modify the `reject` action to convert MODEL_NOT_FOUND code to response
status code 404.

examples/todo-list/test/acceptance/todo-list.acceptance.ts

@@ -110,7 +110,7 @@ describe('Application', () => {
         .expect(200);
       await expect(
         todoListRepo.findById(persistedTodoList.id),
-      ).to.be.rejectedWith(/no TodoList found with id/);
+      ).to.be.rejectedWith(/Model not found: TodoList with id/);
     });
   });
 

examples/todo-list/test/acceptance/todo.acceptance.ts

@@ -96,7 +96,7 @@ describe('Application', () => {
         .send()
         .expect(200);
       await expect(todoRepo.findById(persistedTodo.id)).to.be.rejectedWith(
-        /no Todo found with id/,
+        /Model not found: Todo with id/,
       );
     });
   });

examples/todo/test/acceptance/todo.acceptance.ts

@@ -128,7 +128,7 @@ describe('Application', () => {
         .send()
         .expect(200);
       await expect(todoRepo.findById(persistedTodo.id)).to.be.rejectedWith(
-        /no Todo found with id/,
+        /Model not found: Todo with id/,
       );
     });
   });

packages/repository/src/repositories/legacy-juggler-bridge.ts

@@ -211,7 +211,12 @@ export class DefaultCrudRepository<T extends Entity, ID>
       this.modelClass.findById(id, filter, options),
     );
     if (!model) {
-      throw new Error(`no ${this.modelClass.name} found with id "${id}"`);
+      const quotedId = JSON.stringify(id);
+      const err: Error & {code?: string} = new Error(
+        `Model not found: ${this.modelClass.name} with id ${quotedId}`,
+      );
+      err.code = 'MODEL_NOT_FOUND';
+      throw err;
     }
     return this.toEntity(model);
   }

packages/repository/test/unit/repositories/legacy-juggler-bridge.unit.ts

@@ -45,7 +45,7 @@ describe('DefaultCrudRepository', () => {
 
   class Note extends Entity {
     static definition = new ModelDefinition({
-      name: 'note3',
+      name: 'Note3',
       properties: {
         title: 'string',
         content: 'string',
@@ -281,12 +281,9 @@ describe('DefaultCrudRepository', () => {
 
   it('throws if findById does not return a value', async () => {
     const repo = new DefaultCrudRepository(Note, ds);
-    try {
-      await repo.findById(999999);
-    } catch (err) {
-      expect(err).to.match(/no Note was found with id/);
-      return;
-    }
-    throw new Error('No error was returned!');
+    return expect(repo.findById(999999)).to.be.rejectedWith({
+      message: 'Model not found: Note3 with id 999999',
+      code: 'MODEL_NOT_FOUND',
+    });
   });
 });

packages/rest/src/providers/reject.provider.ts

@@ -11,6 +11,12 @@ import {RestBindings} from '../keys';
 
 const debug = require('debug')('loopback:rest:reject');
 
+// TODO(bajtos) Make this mapping configurable at RestServer level,
+// allow apps and extensions to contribute additional mappings.
+const codeToStatusCodeMapping: {[key: string]: number} = {
+  MODEL_NOT_FOUND: 404,
+};
+
 export class RejectProvider implements Provider<Reject> {
   constructor(
     @inject(RestBindings.SequenceActions.LOG_ERROR)
@@ -22,7 +28,15 @@ export class RejectProvider implements Provider<Reject> {
   }
 
   action({request, response}: HandlerContext, error: Error) {
-    const err = <HttpError>error;
+    const err = error as HttpError & {code?: string};
+
+    if (!err.status && !err.statusCode && err.code) {
+      const customStatus = codeToStatusCodeMapping[err.code];
+      if (customStatus) {
+        err.statusCode = customStatus;
+      }
+    }
+
     const statusCode = err.statusCode || err.status || 500;
     writeErrorToResponse(response, err);
 

packages/rest/test/unit/router/reject.provider.unit.ts

@@ -28,6 +28,18 @@ describe('reject', () => {
     expect(result).to.have.property('statusCode', 500);
   });
 
+  it('converts error code MODEL_NOT_FOUND to status code 404', async () => {
+    const reject = new RejectProvider(noopLogger).value();
+
+    const notFoundError: Error & {code?: string} = new Error('not found');
+    notFoundError.code = 'MODEL_NOT_FOUND';
+
+    reject(contextStub, notFoundError);
+    const result = await contextStub.result;
+
+    expect(result.statusCode).to.equal(404);
+  });
+
   it('logs the error', async () => {
     const logger = sinon.spy() as LogError & SinonSpy;
     const reject = new RejectProvider(logger).value();