On 02/08/2011 07:15, Wolfgang Laun wrote:
2011/7/31 Mark Proctor <mproc...@codehaus.org
<mailto:mproc...@codehaus.org>>
On 31/07/2011 19:39, Wolfgang Laun wrote:
2011/7/31 Mark Proctor <mproc...@codehaus.org
<mailto:mproc...@codehaus.org>>
Implicit mapping I call Managed Object Graphs MOGs. So you
can write
Person( address.street == "my road" )
And that internally would get translated too
$p : Person()
Address( person == $p, street == "my road" )
As there is no doubt that the current explicit bindings
approach on objects is too verbose and hard to read. Nested
accessors add a lot of readability.
So what if Address is not an inserted fact? So far, a CE with
type Foo(...) implied the existence of a fact of that type. I'm
not sure that inserting some object should imply the insertion of
all of its descendants as facts as well...
You don't necessarily have to insert Address. It can attach a
listener, assuming the pojo supported it, when it's accessed in a
pattern - allowing the pattern to receive updates from nested objects.
Surely you mean that changes to Address should result in an update
notification for the owning Person object. - But that's not what I meant.
When the expression is evaluated we could detect that Address is not
inserted and attach a listener to that specific instance, so we can
receive updates for it. So for that rule it would work the same as
Person() Address() yet Address was never inserted. Note that it would be
a lightweight listener just for that join, and not a global insertion.
It could be possible to global insert something too "on demand", but
we'd need something annotation driven to allow the user to specify their
intent.
The LHS
Person(...)
alone fires due a Person inserted and not when an Address is inserted;
it fires again if a Person() update is signalled. In contrast,
Person()
Address(...)
fires after both have been inserted and again after /either one/ has
been updated.
Something can't be inserted anyway unless it has the necessary
references for the joins.
This "references" I doubt very much. Surely you can "insert" anything.
And joins are possible on (primary key attributes as well.
In the case of above Person already has a refernce to Address, so that
can be used. But how do you do a one to many relationship without
correct references?
I want to look at a full range of MOGs to automate and
semi-autimate things with regards to nested structures. At the
moment there is no best practice and DRL (or any other rule
language) does not make this nice. We ALL suck for compact nested
accessors.
The notation a.b.c reflects an implementation technique for a
hierarchical data type. (Traditionally, x-dot-y means "add the offset
for y to the address resulting from x".) A more general concept for
"navigation" in a data structure would have to separate a logical
relationship from the implementation technique. It may be necessary to
retain the "dot" notation for the hard coded access and to devise an
entirely new notation for logical navigation.
As a somewhat contrived example, assume that Address is stored as a
map field with key "addr" and the street is the second text line of
the address:
declare Person
name : String # default implementation as "JBean field"
props : Map
address : Address as props["addr"] # the implementation
end
declare Address
lines : String[]
street : String as lines[1]
end
Person( name == "Psmith", address/street == "Main Drag" )
Car( owner/address/street ... ) # Person owner
Notice that explicitly using
props["addr"]
or
lines[1]
is just another implementation dependent notation which breaks as soon
as someone decides to change it in the class. Such things should not
permeate application code.
Also, notice that a "navigation expression" could be dynamic, making
navigation dependent on the object's state, or whatever.
MOGs could indeed use a different / operator to indicate that they are
relational and to be treated as joins. when we come to implementing
this, we'll have a wider debate on dev mailing list, as it's not
happening in the next few weeks :) Just trying to give people a taste of
directions we can go to improve things.
Mark
-W
Mark
-W
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