fix(core): log abstract entity names during discovery

Closes #4080

packages/core/src/metadata/EntitySchema.ts

@@ -224,7 +224,7 @@ export class EntitySchema<T = any, U = never> {
   }
 
   get name(): EntityName<T>  {
-    return this._meta.name!;
+    return this._meta.className;
   }
 
   /**

tests/issues/GH4080.test.ts

@@ -0,0 +1,87 @@
+import { EntitySchema, SimpleLogger } from '@mikro-orm/core';
+import { MikroORM } from '@mikro-orm/sqlite';
+
+abstract class BaseClass {
+
+  id?: number;
+
+}
+
+interface BaseInterface {
+  id?: number;
+}
+
+class DerivedClass extends BaseClass {
+
+  name?: string;
+
+}
+
+class ImplementingClass implements BaseInterface {
+
+  id?: number;
+  name?: string;
+
+}
+
+const BaseClassSchema = new EntitySchema<BaseClass>({
+  name: 'BaseClass',
+  abstract: true,
+  properties: {
+    id: { type: Number, primary: true },
+  },
+});
+
+const BaseInterfaceSchema = new EntitySchema<BaseInterface>({
+  name: 'BaseInterface',
+  abstract: true,
+  properties: {
+    id: { type: Number, primary: true },
+  },
+});
+
+const DerivedClassSchema = new EntitySchema<DerivedClass>({
+  class: DerivedClass,
+  extends: 'BaseClass',
+  properties: {
+    name: { type: String },
+  },
+});
+
+const ImplementingClassSchema = new EntitySchema<ImplementingClass>({
+  class: ImplementingClass,
+  extends: 'BaseInterface',
+  properties: {
+    name: { type: String },
+  },
+});
+
+let orm: MikroORM;
+
+beforeAll(async () => {
+  const logger = jest.fn();
+  orm = await MikroORM.init({
+    entities: [
+      BaseClassSchema,
+      DerivedClassSchema,
+      BaseInterfaceSchema,
+      ImplementingClassSchema,
+    ],
+    dbName: `:memory:`,
+    logger: msg => logger(msg),
+    loggerFactory: options => new SimpleLogger(options),
+    debug: true,
+  });
+  expect(logger.mock.calls.toString()).not.toMatch('undefined');
+  await orm.schema.refreshDatabase();
+});
+
+afterAll(() => orm.close(true));
+
+test('4080', async () => {
+  orm.em.create(DerivedClassSchema, { name: 'foo' });
+  await orm.em.flush();
+  orm.em.clear();
+
+  await orm.em.findOneOrFail(DerivedClassSchema, { name: 'foo' });
+});