test: add test case for fix of typeorm#6266

test/github-issues/6266/entity/Post.ts

@@ -0,0 +1,14 @@
+import { PrimaryGeneratedColumn, Entity, Column, CreateDateColumn } from "../../../../src";
+
+@Entity()
+export class Post {
+
+    @PrimaryGeneratedColumn()
+    id?: number;
+
+    @Column()
+    title: string;
+
+    @CreateDateColumn()
+    readonly createdAt?: Date;
+}

test/github-issues/6266/issue-6266.ts

@@ -0,0 +1,60 @@
+import "reflect-metadata";
+import {
+    closeTestingConnections,
+    createTestingConnections,
+    reloadTestingDatabases,
+} from "../../utils/test-utils";
+import { Connection } from "../../../src/connection/Connection";
+import { Post } from "./entity/Post";
+import sinon from "sinon";
+import { SelectQueryBuilder } from "../../../src";
+import { assert } from "chai";
+
+describe("github issues > #6266 Many identical selects after insert bunch of items", () => {
+    let connections: Connection[];
+    const posts: Post[] = [
+        {
+            title: "Post 1",
+        },
+        {
+            title: "Post 2",
+        },
+        {
+            title: "Post 3",
+        },
+        {
+            title: "Post 4",
+        },
+    ];
+
+    before(
+        async () =>
+            (connections = await createTestingConnections({
+                entities: [__dirname + "/entity/*{.js,.ts}"],
+                enabledDrivers: ["mysql"],
+            }))
+    );
+    beforeEach(() => reloadTestingDatabases(connections));
+    after(() => closeTestingConnections(connections));
+
+    it("should execute a single SELECT to get inserted default and generated values of multiple entities", () =>
+        Promise.all(
+            connections.map(async (connection) => {
+                const selectSpy = sinon.spy(
+                    SelectQueryBuilder.prototype,
+                    "select"
+                );
+
+                await connection
+                    .createQueryBuilder()
+                    .insert()
+                    .into(Post)
+                    .values(posts)
+                    .execute();
+
+                assert.strictEqual(selectSpy.calledOnce, true);
+
+                selectSpy.restore();
+            })
+        ));
+});