It sounds like you could do something similar-ish to the way sorting is
handled in the sort package with interfaces. Some immediate concerns that
jump out wrt a read and partial update that is done outside the data source:
- partial update implies some form of locking (either optimistic,
distributed, or row level).
- full update will provide a last write wins semantic, whereas a partial
update without locking could result in an undesirable when contended (can
provide an example assuming it's not something you've considers).
Also of note the example data model accommodates for empty values and not
absent values. Nothing wrong just citing it as something you may or may not
want to accommodate.
On Tue, 2 Aug 2016 at 16:58, roger peppe <rogpe...@gmail.com> wrote:
> On 2 August 2016 at 16:46, Guianu Leon <guianul...@gmail.com> wrote:
> > Well I will only get the fields that have to be updated, not the entire
> > object. Therefore I need to get the old object from the database, see
> what
> > has changed, then insert it back.
>
> If you're seeing only the fields that have to be updated, how
> will you know that getting the object will get all the fields?
>
> For example, if I have this object in the database:
>
> {"Age": 10, "Height": 6}
>
> and I do this:
>
> type Person struct {
> Address string
> }
> db.Update("bob", &Person{Address: "12 Some Street"})
>
> then doing a Get into a value of type *Person won't get all the fields
> that you need to update.
>
> I think you'll need a slightly cleverer implementation if you want to do
> this.
> Have you looked into the approach taken by gopkg.in/mgo.v2,
> which addresses a similar problem?
>
> cheers,
> rog.
>
> >
> >
> > On Aug 2, 2016 18:35, "roger peppe" <rogpe...@gmail.com> wrote:
> >>
> >> On 2 August 2016 at 09:58, Rayland <guianul...@gmail.com> wrote:
> >> > I am working in the context of an ODM.
> >> >
> >> > I have an update method, like this:
> >> >
> >> > func Update(key string, valuePtr interface{}) error
> >> >
> >> >
> >> > Inside of this method I need to do a Get in order to get the old
> value,
> >> > compare the modified fields and update them, then insert the new
> object
> >> > in
> >> > the database.
> >> >
> >> > The problem is that inside the Update method I don't know what type
> >> > valuePtr
> >> > is in order to make a second object and feed to the Get method, and
> then
> >> > if
> >> > I call the Get method with an interface{} object it will crash because
> >> > it
> >> > can't Unmarshal (objects are kept as json in the database).
> >>
> >> FWIW Axel's solution can work well and I've use similar techniques in
> >> places,
> >> but I have sympathy for Jan's reservations. Why do you need to do a Get
> >> before doing the Put - how can you tell which fields need to be updated?
> >> I can't immediately see how what you suggest would be different from
> >> just updating the database with the value directly.
> >>
> >> cheers,
> >> rog.
> >>
> >> >
> >> > On Tuesday, August 2, 2016 at 11:26:01 AM UTC+3, Dave Cheney wrote:
> >> >>
> >> >> Hypothetically, if there was a syntax in Go that did this, what would
> >> >> you
> >> >> do next ? In other words, what is the problem you are trying to solve
> >> >> that
> >> >> has lead you to needing this feature?
> >> >>
> >> >> On Tuesday, 2 August 2016 18:18:05 UTC+10, Rayland wrote:
> >> >>>
> >> >>> I basically need something like this:
> >> >>>
> >> >>> var obj = &Person{Name: "John"} // I don't know what type obj will
> be
> >> >>> everytime
> >> >>> var newObj interface{}
> >> >>>
> >> >>> initNewObj(obj) // now newObj is an empty object of type *Person
> >> >>>
> >> >>>
> >> >>>
> >> >>>
> >> >>> On Tuesday, August 2, 2016 at 10:21:01 AM UTC+3, Dave Cheney wrote:
> >> >>>>
> >> >>>> TL;DR a shallow copy is easy, but it's almost never what you want.
> >> >>>>
> >> >>>> https://play.golang.org/p/wpWN3Znop8
> >> >>>>
> >> >>>> Needing to copy an arbitrary value is usually an anti pattern as
> >> >>>> values
> >> >>>> can contain references to other values, which contain references to
> >> >>>> other
> >> >>>> values, which contain references to other values, sometimes leading
> >> >>>> back to
> >> >>>> the previous values.
> >> >>>>
> >> >>>> On Tuesday, 2 August 2016 17:13:21 UTC+10, Rayland wrote:
> >> >>>>>
> >> >>>>> Let's say I have an object A of some type. Is there a way to
> create
> >> >>>>> a
> >> >>>>> new object B with the same type as A without knowing the type of A
> >> >>>>> in
> >> >>>>> advance?
> >> >
> >> > --
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