cayenne-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Ken Anderson <ken.ander...@amphorainc.com>
Subject Re: Staged saves pattern ?
Date Thu, 29 Mar 2018 21:50:50 GMT
Mike,

The docs say to not go too deep with nested contexts, so I don't think that's a viable solution.
 I'm also not clear what benefit you think this would have over the 2 level plan.

Ken

On 3/29/18, 5:39 PM, "Mike Kienenberger" <mkienenb@gmail.com> wrote:

    Instead of having each line as a child context under a parent context,

    parent
    - child1 (line 1)
    - child2 (line 2)
    - child3 (line 3)

    could you have each line processed as a child context of the previous line?

    - child1 (line 1)
    -- child2 (line 2)
    --- child3 (line 3)
    ---- child4 (line 4)

    If you want to "undo" the current line,
    child4.rollbackChangesLocally(); and start on the next line.

    Note that I have not done anything with child contexts, but this would
    be how I'd try to solve it.


    On Wed, Mar 28, 2018 at 9:29 PM, Ken Anderson <ken@anderhome.com> wrote:
    > Hugi,
    >
    > That’s correct - it’s not like we’re just importing a bunch of records.  Each
row in the file could affect the same set of objects.
    >
    > So, we did the child context, but obviously if we created an object in a prior child
and then saved it to the parent, we won’t be able to easily find it in the next child context.
 If you get a localObject in your new child context, it is “hollow”, so not connected
to all the other objects floating around in the parent.  We also can’t fire relationships,
because those relationships will go to the database instead of the parent context.
    >
    > Ken
    >
    >> On Mar 28, 2018, at 7:11 PM, Hugi Thordarson <hugi@karlmenn.is> wrote:
    >>
    >>> That's exactly what we want to do - save once at the end.  However, we have
2 problems:
    >>>
    >>> 1. How do we find the objects that we already created but haven't saved yet
    >>
    >> You can go through yur ObjectContext's newObjects() and filter that to your liking—pretty
much the same as you'd do with EOF.
    >>
    >>> 2. How do we roll back each line if there's an error?  Not a DB error, but
the logic gets so far, and then determines that there's no way to continue so we must skip
this line.
    >>
    >> As you tried yourself, I'd use a child context and commit to the parent once
you're sure everything is in place. Can you explain further what was problematic with that
(that you need to "access the same objects multiple times")? Do you mean that each row of
the file is in some way looking at data from other rows?
    >>
    >> Cheers,
    >> - hugi
    >>
    >>
    >>>
    >>> Ken
    >>>
    >>> On 3/28/18, 6:07 PM, "John Huss" <johnthuss@gmail.com> wrote:
    >>>
    >>>   Well, you could just save once at the end.  Why do you need to save
    >>>   multiple times during the processing?  Validation exceptions and Optimistic
    >>>   Locking errors could be handled in the save with some custom logic and
a
    >>>   retry.
    >>>
    >>>   Or if this isn't a super long process you can use a database transaction
to
    >>>   allow saving multiple times without actually having that data be visible
    >>>   outside of the transaction.
    >>>
    >>>
    >>>   On Wed, Mar 28, 2018 at 6:56 AM Ken Anderson <ken.anderson@amphorainc.com>
    >>>   wrote:
    >>>
    >>>> All,
    >>>>
    >>>> We have a process that reads in a file and, for each line, creates or
    >>>> edits objects in the object graph.  We only want to commit to the database
    >>>> once at the end.
    >>>>
    >>>> We have a finite set of lines, so memory is not an issue.  We need to
save
    >>>> only once because saving will actually fire triggers that will start
doing
    >>>> other things to the database, which will then lead to optimistic lock
    >>>> exceptions for us if we have data that overlaps (which we do).
    >>>>
    >>>> Please don’t suggest we change how the trigger pattern works – it’s
a big
    >>>> system and we don’t have control over it.
    >>>>
    >>>> So, what we’ve toyed with is using a parent/child context arrangement,
    >>>> where each line is processed in a child, and assuming everything goes
OK,
    >>>> we commit only to the parent.  This works well as long as we don’t
need to
    >>>> access the same objects multiple times, but unfortunately, we do.  We
can
    >>>> reach into the parent context’s unsaved objects, but those objects
do not
    >>>> have any relationships since they were built in the child context.  This
    >>>> makes things painful.
    >>>>
    >>>> In EOF, I might consider using a single context and undo, but it doesn’t
    >>>> seem like Cayenne has this kind of functionality.
    >>>>
    >>>> Thoughts?  Suggestions?  In EOF, I had once written a layer that
    >>>> intercepted all queries and tried to find the correct object in unsaved
    >>>> objects, but I don’t have nearly enough experience with Cayenne to
do that.
    >>>>
    >>>> Thanks!
    >>>> Ken
    >>>>
    >>>> Confidentiality Notice: This e-mail and accompanying documents contain
    >>>> confidential information intended for a specific individual and purpose.
    >>>> This e-mailed information is private and protected by law. If you are
not
    >>>> the intended recipient, you are hereby notified that any disclosure,
    >>>> copying, or distribution, or the taking of any action based on the contents
    >>>> of this information, is strictly prohibited.
    >>>>
    >>>
    >>>
    >>> Confidentiality Notice: This e-mail and accompanying documents contain confidential
information intended for a specific individual and purpose. This e-mailed information is private
and protected by law. If you are not the intended recipient, you are hereby notified that
any disclosure, copying, or distribution, or the taking of any action based on the contents
of this information, is strictly prohibited.
    >>
    >


Confidentiality Notice: This e-mail and accompanying documents contain confidential information
intended for a specific individual and purpose. This e-mailed information is private and protected
by law. If you are not the intended recipient, you are hereby notified that any disclosure,
copying, or distribution, or the taking of any action based on the contents of this information,
is strictly prohibited.
Mime
View raw message