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DataContractSerializer and list of abstract class

Plecam de la urmatoarea structura:
public abstract class BaseCar
{
public string Name { get; set; }
}
public class SportCar : BaseCar { }
public class UtilityCar : BaseCar { }
public Foo
{
public Foo()
{
Cars = new List<BaseCar>();
}
public List<BaseCar> Cars { get; set; }
}
...
Foo myFoo = new Foo();
myFoo.Cars.Add( new SportCar());
DataContractSerializer serializer = new DataContractSerializer(typeof(Foo));
serializer.WriteObject(myXmlWriter, myFoo);
Cand nu avem specificat nici un atribut de tip DataContract, toate campurile care sunt publice se serializeaza. In cazul nostru codul se compileaza fara probleme si obtinem un obiect serializat. Problema apare cand vrem sa deserializam obiectul nostru si ne trezim ca proprietatea Cars este null. Chiar daca in constructor inializam aceasta proprietate obtinem in continuare NULL.
Cand ne uitam peste cod realizam ca lucram cu o clasa abstracta, iar in acest caz avem nevoie de atributul KnownTypes pe care il si adaugam sub forma:
[KnownTypes(typeof(SportCar))]
[KnownTypes(typeof(UtilityCar))]
clasei Foo. Cand testam din nou aplicatia nici o schimbare. Daca problema ar fi fost de la KnownTypes, am fi obtinut o eroare specifica care ne spune ca nu se poate serializa/deserializa.
Totusi problema persista si ne horaram sa specificam explicit ce proprietati vrem sa serializam. Clasele noastre ajung sa aibe urmatoarea forma:
[DataContract]
public abstract class BaseCar
{
[DataMember]
public string Name { get; set; }
}
[DataContract]
public class SportCar : BaseCar { }
[DataContract]
public class UtilityCar : BaseCar { }
[KnownTypes(typeof(SportCar))]
[KnownTypes(typeof(UtilityCar))]
[DataContract]
public Foo
{
public Foo()
{
Cars = new List<BaseCar>();
}
[DataMember]
public List<BaseCar> Cars { get; set; }
}
Rulam din nu codul si observam ca acuma totul functioneaza fara nici o problema. Lista noastra de masini este serializata si deserializata fara nici o problema. Am incercat sa caut pe MSDN o locatie unde sa ni se precizeze ca trebuie explicit sa folosim aceste doua atribute cand avem lista de clase abstracte, dar din pacate nu am gasit. Am fost directionat de catre un coleg in urmatoarea locatie unde sunt enumerate regulile deja cunoscute, dar despre acest comportament nu era specificat nimica. http://msdn.microsoft.com/en-us/library/cc656732%28v=vs.100%29.aspx

Comments

  1. Daca tipurile nu sunt abstracte, nu apare problema?
    (sunt o gramada de reguli pentru serializarea colectiilor, da..: http://msdn.microsoft.com/en-us/library/aa347850.aspx )

    ReplyDelete
    Replies
    1. Doar daca avem clase abstracte apare problema.

      Delete

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