Strange error in Ecto.Multi

acrolink

I am trying to load a book, update it and update the associated record like this:

Multi.new()
|> Multi.run(:get_book, fn _ -> Mango.Books.get_book!(line.book_id) end)
|> Ecto.Multi.run(:update_book, fn %{book: book} ->
  Books.update_book(Books.get_book!(book.book_id), %{status: 1})
end)
|> Ecto.Multi.run(:update_associated_record, fn %{book: book} ->
  Records.update_record(Records.get_record!(book.record_id), %{
    returned_at: :os.system_time(:seconds)
  })
end)
|> Repo.transaction()
|> case do
  {:ok, result} -> result
  {:ok, %{book: book}} -> book
  {:ok, %{record: record}} -> record |> whitelist_record_fields
end

This produces this error message:

** (exit) an exception was raised:
    ** (CaseClauseError) no case clause matching: %Mango.Books.Book{__meta__: #Ecto.Schema.Metadata<:loaded, "books">, author: "Waseem", code: 1116, id: 107, inserted_at: ~N[2018-05-05 11:39:49.688053], institute: #Ecto.Association.NotLoaded<association :institute is not loaded>, institute_id: 1, isbn: "13-1234-78", record_id: 17, records: #Ecto.Association.NotLoaded<association :records is not loaded>, status: :out, title: "Hello World", updated_at: ~N[2018-05-25 16:01:41.752519], year: 1982}
        (ecto) lib/ecto/multi.ex:421: Ecto.Multi.apply_operation/5
        (elixir) lib/enum.ex:1899: Enum."-reduce/3-lists^foldl/2-0-"/3
        (ecto) lib/ecto/multi.ex:411: anonymous fn/5 in Ecto.Multi.apply_operations/5
        (ecto) lib/ecto/adapters/sql.ex:576: anonymous fn/3 in Ecto.Adapters.SQL.do_transaction/3
        (db_connection) lib/db_connection.ex:1283: DBConnection.transaction_run/4
        (db_connection) lib/db_connection.ex:1207: DBConnection.run_begin/3
        (db_connection) lib/db_connection.ex:798: DBConnection.transaction/3
        (ecto) lib/ecto/repo/queryable.ex:23: Ecto.Repo.Queryable.transaction/4
        (mango) lib/mango/records/records.ex:112: anonymous fn/1 in Mango.Records.create_record_in/2 # referring to this line: |> Repo.transaction()
..
..

Any idea what might be going on here? Thank you.

18 comments

/phoenix #ecto #ecto_multi

0 3117 18

2018-05-26 08:37:52 UTC

Marked As Solved

Show Best Posts
Show All (oldest first)
Show All (newest first)

OvermindDL1

Update is a different kind of call, it is better to use though, but still, run requires {:ok, result}/{:error, reason} and I bet that one of those were not.

Post #8

Also Liked

OvermindDL1

A couple of things now that I have time to look:

Books.update_book(Books.get_book!(book.book_id), %{status: 1})
What is this returning? An {:ok, result} term?

  Records.update_record(Records.get_record!(book.record_id), %{
    returned_at: :os.system_time(:seconds)
  })

What is this returning? Also an {:ok, result} term?

      {:ok, %{book: book}} -> book
      {:ok, %{record: record}} -> record |> whitelist_record_fields

These will never ever be matched on because {:ok, result} -> result will grab it all first.

Post #7

amnu3387

I think you just need to name your first Multi.run(:get_book... as Multi.run(:book... ?

Post #1

OvermindDL1

The name is how you reference that step in later steps though.

Ecto.Multi very much is a named monadic pipeline.

Elixir really needs some monad stuff built in better so umpteen libraries don’t have to keep remaking it and could just use a behaviour…

Post #3

Last Post!

acrolink

Thanks for sharing, this is the working code:

  multi_result =
    Multi.new() 
    |> Multi.run(:book_to_be_returned, fn _ -> Works.update_book_to_be_returned_multi(line.book_id) end)

and:

def update_book_to_be_returned_multi(book_id) do
alias Mango.Books
alias Mango.Books.Book

case Repo.get_by(Book, %{id: book_id, status: :out}) do
  nil ->
    {:error, %{error: "Book not found or already available.."}}

  book ->
    case Books.update_book(book, %{status: :available}) do
      {:ok, book} -> {:ok, book}  # update_book returns %{:ok, book_object } so this is the correct match
      nil -> {:error, %{error: "Error occured while updating the book.."}}
    end
end

end

Post #18