Re: [EoDsql-users] Adding elements to a (disconnected) DataSet

[Jason M. <le...@gm...>]

Ricardo Palomares wrote:
> Hi,
> 
> First of all, thank you for the 0.9 beta release, Jason. The site new
> look is nicer, too.
> 
> At this moment I have in my program some classes whose persistence I
> wrote before I know about EoDSQL, and I want to change that so all of
> them use EoDSQL. Up to now, every entity in my database model has two
> Java classes (three where EoDSQL is not yet used):
> 
> - ASimpleClass
> - ASimpleClassList
> 
> ASimpleClass represents a single element, whereas ASimpleClassList
> implements or extends things like MutableComboBoxModel or
> AbstractListModel. This way, I have an easy way to put GUI controls
> (JList, JComboBox, etc.) to access to the underlying database table.
> I've even dared to use DataSet as the in-memory list view of the
> database table (I'm using tables with very few rows, 10 or so).
> 
> Now, in a specific entity (VERSION, which represents versions of
> products and could have a UNIQUE constraint on product + version
> fields) I have the need to add a "fake" element, like a "*" wildcard.
> It will be used in a JComboBox and won't be persisted in the VERSION
> table. To put some context on the why I need it, I have another table
> "ROLES" managing permissions, in which I want to be able to have rows
> like:
> 
> Row  Meaning
> --------------------------------------------------------
> 1    UserA is owner of productA, version 1.0
> 2    UserB is owner of productA, version 1.5
> 3    UserA is translator of productB, version 2.0
> 4    UserB is owner of productB, version *
> 
> as a quick way to make userB owner of every possible version of
> productB (row 4), instead of requiring a new row every time a new
> version of productB is created and, at the same time, allow different
> users to be owners of different versions of the same product (rows 1 & 2).
> 
> Obviously, the "*" fake element in the VERSION in-memory list would be
> used in a JComboBox in the ROLES management window.
> 
> Now, I'm not really sure if I could simply add an element to the
> DataSet in disconnected mode and use it in the JComboBox model like a
> simple List. I never write back the DataSet to disk; every time a
> record is added, modified or deleted, the query is re-executed and the
> DataSet is disconnected. I *believe* I may be in the safe side, but I
> don't really know for sure. Is this a sensible approach?
> 
> TIA
> 
> 
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I would say that a possibly more sensible approach would be to implement the
"fake" element in the Swing list/combobox model itself. If the element number
request is 0, then return the "fake" element to display, otherwise return
DataSet.get(row - 1); If that makes sense?

You may want to implement a single combobox model and a list model which accepts
a model of the same type and adds a fake element to the beginning of the list. A
FakeElementComboBoxModel for example.

You can't add elements to a DataSet in EoDSQL at all, it'll throw an
UnsupportedOperationException since all DataSet's are considered to be
read-only. It's a deviation from the EoD RI which did allow read/write
DataSet's. I will implement read/write DataSets some day, but for the time being
they're a lot of overhead for what I say as very little functionality (for now).

Hope the idea helps  ;)