Re: Fast and Easy way to check if an instance of an Model exists in the Database

pk is not necessarily id, in any case if you are the one adding it then you already know that the object didn't come from the db, in order to check that later I would add an attribute to the object and check it's presence, if not present it means it came from the db.

On Tue, Jan 21, 2014 at 11:55 AM, Johannes Schneider <johannes.schneider@galileo-press.de> wrote:

yes, but the problem is that we manually give them a pk.

Maye it's the best to reduce the question to the following:
Which (undocumented) field is better for this case?
* instance._state.db (checking if this is None)
* instance_state.adding (checking for True)

bg,
Johannes

On 21.01.2014 10:07, Avraham Serour wrote:

wouldn't checking for the presence of an id enough? as far as I know
instantiated objects don't have id's


On Tue, Jan 21, 2014 at 10:16 AM, Erik Cederstrand

<erik+lists@cederstrand.dk <mailto:erik+lists@cederstrand.dk>> wrote:

    Den 21/01/2014 kl. 08.58 skrev Johannes Schneider
    <johannes.schneider@galileo-press.de

    <mailto:johannes.schneider@galileo-press.de>>:

     > maybe I I formulated it not precise enough.
     > I need to check if some instance of a model comes from some
    database query (e.g. via get(..)) or is instanciated 'by hand'. and
    not jet written to the database.
     > In this case I don't need to know, if there is an related object
    (e.g. with the same pk or same values for its attributes) in the
    database.

    Okay. Sounds like your best bet is to either roll your own, or use
    the undocumented API as suggested by Tom Evans.

    Either way, make sure to write tests so this doesn't break when you
    upgrade Django.

    Erik

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