use dataloader to collect calls to DB fixes #30

[Kkoile]

Using the dataloder module the calls to the DB are minimized without needing to refactor the code too much.

This fixes the performance issues which occur in drafActivate ( see #30 )

I would love to write a test, but it seems jest is not fully supported in this project.

it("should only optimize reads to the DB", async () => {
    const action1 = POST.bind(
      {},
      `/odata/v4/admin/BookStores(ID=64625905-c234-4d0d-9bc1-283ee8946770,IsActiveEntity=false)/books`,
      {
        ID: "9d703c23-54a8-4eff-81c1-cdce6b8376b2",
        title: "test title 1",
        descr: "test descr",
        author_ID: "d4d4a1b3-5b83-4814-8a20-f039af6f0387",
        stock: 1,
        price: 1.0,
        isUsed: true
      }
    );
    const action2 = POST.bind(
      {},
      `/odata/v4/admin/BookStores(ID=64625905-c234-4d0d-9bc1-283ee8946770,IsActiveEntity=false)/books`,
      {
        ID: "3e53bf3b-53f7-4db8-87ce-8bb0818574d8",
        title: "test title 2",
        descr: "test descr",
        author_ID: "d4d4a1b3-5b83-4814-8a20-f039af6f0387",
        stock: 1,
        price: 1.0,
        isUsed: true
      }
    );
    const cdsRunSpy = jest.spyOn(cds.db, "run")
    await utils.apiAction("admin", "BookStores", "64625905-c234-4d0d-9bc1-283ee8946770", "AdminService", [action1, action2]);
    // `toHaveBeenCalledWith` is not working in this project
    expect(cdsRunSpy).toHaveBeenCalledWith([expect.objectContaining({
      SELECT: {
        from: expect.objectContaining({ref: ["AdminService.Books"]}),
        where: [expect.objectContaining({ref: ["ID"]}), "in", {list: [{val: "9d703c23-54a8-4eff-81c1-cdce6b8376b2"}, {val: "3e53bf3b-53f7-4db8-87ce-8bb0818574d8"}]}]
      }
    })])
  });

[nkaputnik]

Hello @Kkoile
thank you very much for this contribution, this looks quite elegant.
I have to check, though, for the use of the dataloader library, and whether this is something we can include here...
I'll ask @Sv7enNowitzki to modify the test so it works in the CAP context

Best,
Nick