What is the recommended approach to to copy or 'save as' a record using ReStore? Using #copy or #deepCopy just seems to update the original.

I have tried creating a new, 'empty' object of a class and populating just the fields of interest, which seems to work sometimes, but other times results in either an 'index of bounds' error or fails trying to (re-) insert a duplicate key value in a related table.

Thanks in advance for any and all ideas.

Regards,
Scott

Hi Scott,

When copying objects in Smalltalk you may also need to copy some component objects to ensure the copy has a sensible structure. This is particularly important when copying objects persisted with ReStore (in some cases ReStore will complain about invalid structures) however the principle is the same as for non-persistent objects.

As an example I'll use the classes from the "SSW ReStore Examples" package (see the package comment for more details). Starting with an empty database let's first create a Customer with an Address:

Customer new
firstName: 'John';
surname: 'Smith';
address: (Address new line1: '123 Oxford Street'; yourself);
store.

You should now have a database containing one Customer and one Address:

Customer storedInstances size. "1"
Address storedInstances size. "1"

Now let's try to copy the customer and persist the copy:

customer := Customer storedInstances first.
copy := customer copy.
copy firstName: 'James'; store.

At this point you should receive the error "attempt to assign collection to > 1 persistent object". This is because the default implementation of copy will just return a shallowCopy, so the copy has the exact same 'orders' collection as the original. Sharing persistent collections isn't valid in ReStore so the copy needs its own collection - we do this by adding an implementation of postCopy to Customer:

postCopy

super postCopy.
self orders: OrderedCollection new

We should now be able to create and persist a new copy of the customer:

copy := customer copy.
copy firstName: 'James'; store.

However note that although we've copied the customer the address has not been copied:

Customer storedInstances size. "2"
Address storedInstances size. "1"

The single persistent Address is shared by both customers (it's valid to share persistent non-collection objects in ReStore). It may be that this would be a valid situation in some databases, however for a database of customers lets assume we want each customer to have its own independent address, so we should also copy the address as part of the customer's postCopy method:

postCopy

super postCopy.
self orders: OrderedCollection new.
self address: self address copy

If we now create and persist an additional copy we will get both a new customer and a new address:

copy := customer copy.
copy firstName: 'Jack'; store.

Customer storedInstances size. "3"
Address storedInstances size. "2"

Just to reiterate, the important thing is to implement postCopy methods in your persistent classes so that the resulting copies represent a valid structure according to the requirements of your data model.

Hope this helps,

John Aspinall

On Wednesday, September 13, 2023 at 9:05:33 PM UTC+1, Scott McWilliams wrote:
> What is the recommended approach to to copy or 'save as' a record using ReStore? Using #copy or #deepCopy just seems to update the original.
>
> I have tried creating a new, 'empty' object of a class and populating just the fields of interest, which seems to work sometimes, but other times results in either an 'index of bounds' error or fails trying to (re-) insert a duplicate key value in a related table.
>
> Thanks in advance for any and all ideas.
>
> Regards,
> Scott

On Friday, September 15, 2023 at 11:14:25 AM UTC-5, john.a...@gmail..com wrote:
> Hi Scott,
>
> When copying objects in Smalltalk you may also need to copy some component objects to ensure the copy has a sensible structure. This is particularly important when copying objects persisted with ReStore (in some cases ReStore will complain about invalid structures) however the principle is the same as for non-persistent objects.
>
> As an example I'll use the classes from the "SSW ReStore Examples" package (see the package comment for more details). Starting with an empty database let's first create a Customer with an Address:
>
> Customer new
> firstName: 'John';
> surname: 'Smith';
> address: (Address new line1: '123 Oxford Street'; yourself);
> store.
>
> You should now have a database containing one Customer and one Address:
>
> Customer storedInstances size. "1"
> Address storedInstances size. "1"
>
> Now let's try to copy the customer and persist the copy:
>
> customer := Customer storedInstances first.
> copy := customer copy.
> copy firstName: 'James'; store.
>
> At this point you should receive the error "attempt to assign collection to > 1 persistent object". This is because the default implementation of copy will just return a shallowCopy, so the copy has the exact same 'orders' collection as the original. Sharing persistent collections isn't valid in ReStore so the copy needs its own collection - we do this by adding an implementation of postCopy to Customer:
>
> postCopy
>
> super postCopy.
> self orders: OrderedCollection new
>
> We should now be able to create and persist a new copy of the customer:
>
> copy := customer copy.
> copy firstName: 'James'; store.
>
> However note that although we've copied the customer the address has not been copied:
>
> Customer storedInstances size. "2"
> Address storedInstances size. "1"
>
> The single persistent Address is shared by both customers (it's valid to share persistent non-collection objects in ReStore). It may be that this would be a valid situation in some databases, however for a database of customers lets assume we want each customer to have its own independent address, so we should also copy the address as part of the customer's postCopy method:
>
> postCopy
>
> super postCopy.
> self orders: OrderedCollection new.
> self address: self address copy
>
> If we now create and persist an additional copy we will get both a new customer and a new address:
>
> copy := customer copy.
> copy firstName: 'Jack'; store.
>
> Customer storedInstances size. "3"
> Address storedInstances size. "2"
>
> Just to reiterate, the important thing is to implement postCopy methods in your persistent classes so that the resulting copies represent a valid structure according to the requirements of your data model.
>
> Hope this helps,
>
> John Aspinall
> On Wednesday, September 13, 2023 at 9:05:33 PM UTC+1, Scott McWilliams wrote:
> > What is the recommended approach to to copy or 'save as' a record using ReStore? Using #copy or #deepCopy just seems to update the original.
> >
> > I have tried creating a new, 'empty' object of a class and populating just the fields of interest, which seems to work sometimes, but other times results in either an 'index of bounds' error or fails trying to (re-) insert a duplicate key value in a related table.
> >
> > Thanks in advance for any and all ideas.
> >
> > Regards,
> > Scott

Thank you John!

Regards,
Scott