MEHUL.JAIN

MEHUL.JAIN

Select For Update in Elixir Transaction

I am trying to avoid deadlock between my Ecto Transaction operating on the same Table. To do that I am trying to replicate Postgres “Select … for Update” in Ecto Multi.
Question is: Can I avoid lock here?

Query:

    query =
      from(s in Split,
        where: <condition>
        lock: fragment("FOR UPDATE OF ?", s),
        order_by: [asc: :id],
        select: %{
          id: s.id
        }
      )

    Repo.multi_update_all(
      multi,
      :updated_splits,
      from(s in Split,
        join: t in subquery(query),
        on: s.id == t.id,
        update: [
          set: [
            ....
          ]
        ]
       ),
      []
    )

First Post!

zachdaniel

zachdaniel

Creator of Ash

AFAIK there is no difference between locking for update and selecting for update, if that is what you are getting at. Beyond that, to tell you if you can avoid the lock from a bigger picture perspective, I’d need to know a lot more about how it all fit together.

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