How to use transaction through multiple services?

[maxinmos]

Hello, thanks for great series.
But currently, you use transaction in every query inside services. So how to use transaction through multiple services?
Example:

tx, _ := d.Begin()

// store file
fileStorageService.SaveImage("/avatar.jpg")

// database stuffs
userService.CreateUser(user)

// other database stuffs
...

tx.Commit()

[benbjohnson]

Good question. I typically make my service methods implement a transactional boundary so that I don't need to share the transaction outside of it. In the example you have, you don't have a shared transaction as the fileStorageService isn't likely transactional (assuming it's disk-backed or S3-backed). You can end up with the file on your storage service but your CreateUser() could fail.

You could model your Tx inside your application domain but that assumes that all your services that use myapp.Tx are transactional. Transactions really only make sense within a single service (e.g. a sqlite layer) as you can't easily implement transactions across multiple layers or implementations.

[maxinmos]

Thanks very much for your answer.
How do you think about "transaction per request" pattern (https://goenning.net/2017/06/20/session-per-request-pattern-go).
In .NET Entity Framework, DbContext is created per request, but I don't know why it's not common in Go.

[benbjohnson]

I personally dislike having the HTTP layer know too much about the underlying data access. Typically, I structure my HTTP handlers to only handle the transport (e.g. encoding/decoding) and that just hands off to the service implementation.

For example, in the WTF Dial repo the data access for HTTP handlers is pretty minimal:

• wtf/http/dial.go

  Lines 63 to 68 in daadc79

  	// Fetch dials from database.
  	dials, n, err := s.DialService.FindDials(r.Context(), filter)
  	if err != nil {
  	Error(w, r, err)
  	return
  	}

• wtf/http/dial.go

  Lines 117 to 129 in daadc79

  	// Fetch dial from the database.
  	dial, err := s.DialService.FindDialByID(r.Context(), id)
  	if err != nil {
  	Error(w, r, err)
  	return
  	}
  	// Fetch associated memberships from the database.
  	dial.Memberships, _, err = s.DialMembershipService.FindDialMemberships(r.Context(), wtf.DialMembershipFilter{DialID: &dial.ID})
  	if err != nil {
  	Error(w, r, err)
  	return
  	}

• wtf/http/dial.go

  Lines 171 to 172 in daadc79

  	// Create dial in the database.
  	err := s.DialService.CreateDial(r.Context(), &dial)

• wtf/http/dial.go

  Lines 218 to 223 in daadc79

  	// Fetch dial from the database.
  	dial, err := s.DialService.FindDialByID(r.Context(), id)
  	if err != nil {
  	Error(w, r, err)
  	return
  	}

• wtf/http/dial.go

  Lines 246 to 255 in daadc79

  	// Update the dial in the database.
  	dial, err := s.DialService.UpdateDial(r.Context(), id, upd)
  	if wtf.ErrorCode(err) == wtf.EINTERNAL {
  	Error(w, r, err)
  	return
  	} else if err != nil {
  	tmpl := html.DialEditTemplate{Dial: dial, Err: err}
  	tmpl.Render(r.Context(), w)
  	return
  	}

• wtf/http/dial.go

  Lines 274 to 278 in daadc79

  	// Delete the dial from the database.
  	if err := s.DialService.DeleteDial(r.Context(), id); err != nil {
  	Error(w, r, err)
  	return
  	}

• wtf/http/dial.go

  Lines 307 to 311 in daadc79

  	// Update value for the user's membership on the dial.
  	if err := s.DialService.SetDialMembershipValue(r.Context(), id, jsonRequest.Value); err != nil {
  	Error(w, r, err)
  	return
  	}

[maxinmos]

I see, thanks a lot.