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

[Sv7enNowitzki]

Hi @Kkoile

I have fixed the related issues so that the unit test you provided can run in the project. Could you also check if the unit test I added is what you wanted?

Also, ping @nkaputnik for reference.

Best Regards,
Wenjun

[Kkoile]

@Sv7enNowitzki the changes look good to me. Thanks!
What are the next steps? Do you think it is okay to use the dataloader dependency?

[Sv7enNowitzki]

Hi @nkaputnik ,

Could you please share the latest updates?

Best Regards,
Wenjun

[nkaputnik]

Hello, I'm still waiting for approval to use the external dataloader library.
Since most resources in the CAP team are bound with other, more pressing projects right now, this is unfortunately low on then priority list.
I'll be happy to merge this PR as soon as I have clarity on how to use this OSS lib.

Best,
Nick