Hello!
4) It is not mandatory to register/map class A.
If you want some code to be shared across several persistence classes,
you can also create a persistence field and use it in both classes:
namespace Wt {
namespace Dbo {
template <class Action>
void field(Action& action, Coordinate& coordinate, const std::string& name,
int size = -1)
{
field(action, coordinate.x, name + "_x");
field(action, coordinate.y, name + "_y");
}
}
}
(this example is taken from
http://www.webtoolkit.eu/wt/doc/git/tutorial/dbo/tutorial.html#_specifying_a_composite_natural_primary_key)
Then, you can use class Coordinate in your persistence classes:
class A {
public:
Coordinate c;
template<class Action>
void persist(Action& a) {
dbo::field(a, c, "c");
}
};
This should create two fields: c_x and c_y in database table.
2012/4/24 Tero Mäntyvaara <[email protected]>:
> Hi,
>
>
> thank you for your reply! 4) Is it mandatory to register/map class A in
> your example? This way it is possible to create base class that is
> abstract in persistence level.
>
>
> Tero
>
> On 23.4.2012 17:41, Nagaev Boris wrote:
>> Hello!
>>
>> 2,3) No. Abstract class can not be mapped to database. I think,
>> reading from database is implemented as follows: Wt::Dbo creates
>> instance of mapped C++ class using default constructor and then
>> applies .persist() method to set values from database to all fields of
>> this instance. Instance of abstract class can not be created, so we
>> get a compile error.
>>
>> 1) Possible (see example)
>> For each class (base and descendant), you should create a separate
>> table in database.
>> Add method .persist() to descendant class, which calls .persist()
>> method of its base class:
>>
>> class A {
>> public:
>> int x;
>>
>> template<class Action>
>> void persist(Action& a) {
>> dbo::field(a, x, "x");
>> }
>> };
>>
>> class B : public A {
>> public:
>> int y;
>>
>> template<class Action>
>> void persist(Action& a) {
>> A::persist(a);
>> dbo::field(a, y, "y");
>> }
>> };
>>
>> session.mapClass<A>("class_a");
>> session.mapClass<B>("class_b");
>>
>> Inheritance seems to work even if base class was inherited from
>> dbo::Dbo<A> template, but this is not documented.
>> http://www.webtoolkit.eu/wt/doc/reference/html/classWt_1_1Dbo_1_1Dbo.html
>>
>>
>> 2012/4/23 Tero Mäntyvaara <[email protected]>:
>>> Hi,
>>>
>>> I have three questions about inheritance and abstraction: is it possible...
>>> 1) ...to Wt::Dbo persistence class be inherited from another?
>>> 2) ...to make persistence class abstract?
>>> 3) ...inherit persistence class from abstract persistence class?
>>>
>>>
>>> Tero
>>>
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