How to rewrite this using the pipe operator

Phoenix Forum Questions / Help
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1

I have this piece of code which increments some serial like value called book_code_serial.

institute = Repo.one(from i in Mango.Institutes.Institute, where: i.id == 1)
changeset = Mango.Institutes.Institute.book_code_serial_changeset(institute, %{book_code_serial: institute.book_code_serial + 1})
Repo.update!(changeset)

Works fine, but I want to know how this can be rewritten using the ‘|>’ operator, specifically how to do %{book_code_serial: institute.book_code_serial + 1} inside the pipe. Thank you.

2

Are you sure you should?

What if institute == nil, which is a valid return value from Repo.one?

case Repo.one(...) do
  nil -> 
    ...

  institute ->
    changeset = ...
    Repo.update!(changeset)
end
3

It would just be:

from(i in Mango.Institutes.Institute, where: i.id == 1)
|> Repo.one()
|> (&Mango.Institutes.Institute.book_code_serial_changeset(&1, %{book_code_serial: &1.book_code_serial + 1})).()
|> Repo.update!()

Or:

from(i in Mango.Institutes.Institute, where: i.id == 1)
|> Repo.one()
|> case do in -> Mango.Institutes.Institute.book_code_serial_changeset(in, %{book_code_serial: in.book_code_serial + 1}) end
|> Repo.update!()

Or a few other things you can do, or just make a specialized function for that call as it looks pattern’y. :slight_smile:

1 Like
4

Thank you very much. Similarly it can be done using:

Repo.one(from i in Mango.Institutes.Institute, where: i.id == 1) |>
(fn institute -> Mango.Institutes.Institute.book_code_serial_changeset(institute, %{book_code_serial: institute.book_code_serial + 1}) end).() |>
Repo.update!()
1 Like
5

Use a named function instead of an anonymous one. It will be much easier to read.

2 Likes