Why are properties without a setter not serialized

Question

I have a serializable class and one of the properties in my class generates a Guid in the getter. The property implements no setter and is ignores during serialization. Why is that and do I always have to implement a setter in order for my property to be serialized.

[Serializable]
public class Example
{
    [XmlAttribute("id")]
    public string Id
    {
        get
        {
             return Guid.NewGuid().ToString();
        }
    }
}

I tried implementing an empty setter and it got serialized correctly.

[Serializable]
public class Example
{
    [XmlAttribute("id")]
    public string Id
    {
        get
        {
             return Guid.NewGuid().ToString();
        }
        set {}
    }
}

Update:

Can you point out how should I define properties whose values never change or ones that the value for is generated internally?

The second example serialize correctly... But what happen when you try to deserialize it? — LightStriker, Nov 15 '12 at 15:54
Try YAXLib [[+](https://github.com/sinairv/YAXLib/),[+](http://www.codeproject.com/Articles/34045/Yet-Another-XML-Serialization-Library-for-the-NET)] — Sina Iravanian, Nov 15 '12 at 15:55
Also see [force-xml-serialization-to-serialize-readonly-property](http://stackoverflow.com/questions/5585364/force-xml-serialization-to-serialize-readonly-property), and [can-an-internal-setter-of-a-property-be-serialized](http://stackoverflow.com/questions/420662/can-an-internal-setter-of-a-property-be-serialized) — nawfal, Jul 12 '14 at 11:24

score 65 · Accepted Answer · answered Nov 15 '12 at 15:53

65

It's a limitation of XmlSerializer it doesn't serialize read-only properties, what you have done in your second example is essentially the hack to get it to serialize, however, it's useless if you need it to deserialize later.

Alternatively you could switch to using DataContractSerializer, it's more flexible.

answered Nov 15 '12 at 15:53

James

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DataContractSerializer also requires setters. This is a limitation because even though we may use it for only one type of operation, say deserialization, but the declarations need to be for both otherwise, the serialization process will not know what to do with a value when it is trying to serialize an XML into objects. – Ravi Y Nov 15 '12 at 15:55
7

@ryadavilli anything marked as `[DataMember]` is serialized using `DataContractSerializer` (read-only or not). – James Nov 15 '12 at 15:59
@James So if I use DataMember attribute it would be serialized? – Konstantin Dinev Nov 15 '12 at 16:02
@KonstantinD-Infragistics yes if you decorate your model as is (i.e. without the setter) and replace your `[XmlAttribute]` attribute with `[DataMember]` it will work. – James Nov 15 '12 at 16:09
1

@James I wrote the above because i got some compile time errors when I tried the same. Now, when I got back to my code and removed the setter, it seems to compiling fine. This is very wierd and probably homework for me to research more on this. – Ravi Y Nov 15 '12 at 16:13
3

Ahhh finally found the source of my confusion. A property setter is not required for serialization. However, if a property does not have a setter, the XML will not deserialize to an object. There, homework finished. – Ravi Y Nov 15 '12 at 16:24
1

@ryadavilli yep exactly, it's just a limitation of the `XmlSerializer` implementation, it relies on the public setter method. `DataContractSerializer` is a bit more clever in that sense (probably using reflection to set the field behind the scenes). – James Nov 15 '12 at 18:11
1

As far as I know DataContractSerializer serializes all Properties as Elements. Attributes are not supported. But in the original post the property is supposed to be serialized as [XmlAttribute("id")]. – sth_Weird Feb 10 '16 at 08:33
@sth_Weird yeah that's correct, that's why my answer states "*it's more flexible*" - it doesn't serialize attributes out the box but you can extend it to do so. – James Feb 10 '16 at 15:34

score 11 · Answer 2 · edited Jun 20 '20 at 09:12

See "Introducing XML Serialization" in the MSDN documentation. Among other things, it says:

Items That Can Be Serialized

The following items can be serialized using the XmlSerializer class:
Public read/write properties and fields of public classes.

Classes that implement ICollection or IEnumerable.
Note:
Only collections are serialized, not public properties.
XmlElement objects.

XmlNode objects.

DataSet objects.

Also, see "Why XML-Serializable class need a parameterless constructor"

Also, IXmlSerializable

In addition to the above types which can be serialized by the XML Serializer, any type which implements the IXmlSerializable interface can be serialized and deserialized. In particular, this means that the XElement and XDocument types can be serialized.

See "IXmlSerializable Interface".

score 6 · Answer 3 · answered Nov 15 '12 at 16:05

6

Limitation of XMLSerializer - Properties without setter can't be serialized.

But you can use DataContractSerializer to serialize private setter properties -

[DataMember]
public string Id
{
    get
    {
         return Guid.NewGuid().ToString();
    }
    private set {}
}

answered Nov 15 '12 at 16:05

Rohit Vats

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The property is supposed to be serialized as an xml-attribute (see original post). Your code (DataMember attribute) produces an xml-element. As far as I know there is no (clean) way to tell the DataContractSerializer to turn a property into an attribute and not an element. DataContractSerializer is nice but you always have to keep this limitation in mind. – sth_Weird Feb 10 '16 at 08:38

score 2 · Answer 4 · edited May 23 '17 at 11:53

2

if you want to have private setters, and have the object be serializable/deserializable, impliment ISerializable, and create a constructor like MyObject(SerializationInfo info, StreamingContext context). An example is found here.

edited May 23 '17 at 11:53

Community

1
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answered Sep 20 '13 at 20:06

edamon

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4

score 0 · Answer 5 · answered Nov 15 '12 at 15:56

Serialization attributes are used to serialize and deserialize objects. XmlSerializer will assume that you don't need to serialize any property that doesn't have a setter. Setter will be used when deserializing a string into an object, because an instance of the object needs to be created and then the setter will be used to populate the property value.

Why are properties without a setter not serialized

5 Answers5

Items That Can Be Serialized

Note:

Also, IXmlSerializable

Linked

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