fix: save correct discriminator with STI

When using a STI scheme and an EntityManager or Repository
with base class target, the wrong discriminator was written to the
database despite giving an concrete entity.
This was because of the entity's target being ignored in favor of the
target of the Repository or the EntityManager.

fixes typeorm#2927

src/persistence/EntityPersistExecutor.ts

@@ -81,10 +81,23 @@ export class EntityPersistExecutor {
                         if (entityTarget === Object)
                             throw new CannotDetermineEntityError(this.mode)
 
+                        var metadata = this.connection.getMetadata(entityTarget)
+
+                        // Check for single table inheritance and find the correct metadata in that case.
+                        // Goal is to use the correct discriminator as we could have a repository
+                        // for an (abstract) base class and thus the target would not match.
+                        if (metadata.inheritancePattern === 'STI' && metadata.childEntityMetadatas.length > 0) {
+                            const matchingChildMetadata = metadata.childEntityMetadatas.find((meta) =>
+                                entity.constructor === meta.target
+                            )
+                            if (matchingChildMetadata) {
+                                metadata = matchingChildMetadata
+                            }
+                        }
+
                         subjects.push(
                             new Subject({
-                                metadata:
-                                    this.connection.getMetadata(entityTarget),
+                                metadata,
                                 entity: entity,
                                 canBeInserted: this.mode === "save",
                                 canBeUpdated: this.mode === "save",

test/github-issues/2927/entity/Content.ts

@@ -0,0 +1,20 @@
+import { Column, Entity, PrimaryGeneratedColumn, TableInheritance } from "../../../../src"
+
+export enum ContentType {
+    Photo = 'photo',
+    Post = 'post',
+    SpecialPhoto = 'special_photo',
+}
+
+@Entity()
+@TableInheritance({ pattern: 'STI', column: { type: 'enum', name: "content_type", enum: ContentType } })
+export class Content {
+    @PrimaryGeneratedColumn()
+    id: number
+
+    @Column()
+    title: string
+
+    @Column()
+    description: string
+}

test/github-issues/2927/entity/Photo.ts

@@ -0,0 +1,8 @@
+import { ChildEntity, Column } from "../../../../src";
+import { Content, ContentType } from "./Content";
+
+@ChildEntity(ContentType.Photo)
+export class Photo extends Content {
+    @Column()
+    size: number
+}

test/github-issues/2927/entity/Post.ts

@@ -0,0 +1,8 @@
+import { ChildEntity, Column } from "../../../../src";
+import { Content, ContentType } from "./Content";
+
+@ChildEntity(ContentType.Post)
+export class Post extends Content {
+    @Column()
+    viewCount: number
+}

test/github-issues/2927/entity/SpecialPhoto.ts

@@ -0,0 +1,9 @@
+import { ChildEntity, Column } from "../../../../src";
+import { ContentType } from "./Content";
+import { Photo } from "./Photo";
+
+@ChildEntity(ContentType.SpecialPhoto)
+export class SpecialPhoto extends Photo {
+    @Column()
+    specialProperty: number
+}

test/github-issues/2927/issue-2927.ts

@@ -0,0 +1,37 @@
+import "reflect-metadata";
+import { createTestingConnections, closeTestingConnections, reloadTestingDatabases } from "../../utils/test-utils";
+import { DataSource } from "../../../src/data-source/index";
+import { expect } from "chai";
+import { Content } from "./entity/Content";
+import { Photo } from "./entity/Photo";
+
+describe("github issues > #2927 When using base class' custom repository, the discriminator is ignored", () => {
+
+    let dataSources: DataSource[];
+    before(async () => dataSources = await createTestingConnections({
+        entities: [__dirname + "/entity/*{.js,.ts}"],
+        schemaCreate: true,
+        dropSchema: true,
+    }));
+    beforeEach(() => reloadTestingDatabases(dataSources));
+    after(() => closeTestingConnections(dataSources));
+
+    it("should use the correct subclass for inheritance when saving and retrieving concrete instance",() =>
+        Promise.all(dataSources.map(async dataSource => {
+            const entityManager = dataSource.createEntityManager();
+            const repository = entityManager.getRepository(Content);
+
+            // Create and save a new Photo.
+            const photo = new Photo();
+            photo.title = 'some title';
+            photo.description = 'some description';
+            photo.size = 42;
+            await repository.save(photo);
+
+            // Retrieve it back from the DB.
+            const contents = await repository.find();
+            expect(contents.length).to.equal(1);
+            expect(contents[0] instanceof Photo).to.equal(true);
+        }
+    )));
+});