I have a a property defined as:
[XmlArray("delete", IsNullable = true)]
[XmlArrayItem("contact", typeof(ContactEvent)),
XmlArrayItem("sms", typeof(SmsEvent))]
public List<Event> Delete { get; set; }
If the List<> Delete has no items
<delete />
is emitted. If the List<> Delete is set to null
<delete xsi:nil="true" />
is emitted. Is there a way using attributes to get the delete element not to be emitted if the collection has no items?
Greg - Perfect thanks, I didn't even read the IsNullable documentation just assumed it was signalling it as not required.
Rob Cooper - I was trying to avoid ISerializable, but Gregs suggestion works. I did run into the problem you outlined in (1), I broke a bunch of code by just returning null if the collection was zero length. To get around this I created a EventsBuilder class (the class I am serializing is called Events) that managed all the lifetime/creation of the underlying objects of the Events class that spits our Events classes for serialization.
I've had the same issue where I did not want an element outputted if the field is empty or 0.
The XML outputted could not use xsi:null="true" (by design).
I've read somewhere that if you include a property of type bool with the same name as the field you want to control but appended with 'Specified', the XMLSerializer will check the return value of this property to determine if the corresponding field should be included.
To achieve this without implementing IXMLSerializer:
public List<Event> Delete { get; set; }
[XMLIgnore]
public bool DeleteSpecified
{
get
{
bool isRendered = false;
if (Delete != null)
{
isRendered = (Delete.Count > 0);
}
return isRendered;
}
set
{
}
}
If you set IsNullable=false or just remove it (it is false by default), then the "delete" element will not be emitted. This will work only if the collection equals to null.
My guess is that there is a confusion between "nullability" in terms of .NET, and the one related to nullable elements in XML -- those that are marked by xml:nil attribute. XmlArrayAttribute.IsNullable property controls the latter.
First off, I would say ask yourself "What is Serialization?".
The XmlSerializer is doing exactly what it is supposed to be doing, persisting the current state of the object to XML. Now, I am not sure why the current behaviour is not "right" for you, since if you have initialized the List, then it is initialized.
I think you have three options here:
Add code to the Getter to return null if the collection has 0 items. This may mess up other code you have though.
Implement the IXmlSerializable interface and do all the work yourself.
If this is a common process, then you may want to look at my question "XML Serialization and Inherited Types" - Yes, I know it deals with another issue, but it shows you how to create a generic intermediary serialization class that can then be "bolted on" to allow a serilization process to be encapsulated. You could create a similar class to deal with overriding the default process for null/zero-item collections.
I hope this helps.
You could always implement IXmlSerializer and perform the serialization manually.
See http://www.codeproject.com/KB/cs/IXmlSerializable.aspx for an example.
Related
I have an C# object that hold a big list (10-100MB) and some other properties. I want to serialize the object, but I don't want to serialize the list. is there any easy way to do that?
Thanks!
Since it is tagged xml, this could be as simple as adding [XmlIgnore] to the appropriate property:
[XmlIgnore]
public List<Foo> Items {get;set;}
Then just use XmlSerializer as normal.
If it needs to be controllable (sometimes yes, sometimes no) then an alternative is to add:
public bool ShouldSerializeItems() {
// your logic here
}
This pattern is recognised by many serializers, XmlSerializer included.
If you mean by serialization loading the object from database, then I can recommend NHibernate, you simply mark, you want to enable lazy-loading on the List and your object will return, with Items set to null (and if you are still in transaction, Items will load, after and only after attempting to access it; if you are out of transaction already, you will get a nullPointer exception I think)... but basically, Lazy-loading in any its kind is certainly a principle, you should keep an eye on.
EDIT: missed the tags, shame on me
I do not think this is a duplicate. I have done some reading but did not find anything the same as this. It seems that fields can be serialized in binary formatters and in protobuf but not in XML. I don't know about JSON.
I am looking at replacing the standard .NET binary serializer with protobuf-net. The reason is to improve speed and get a smaller persisted file size.
In NET Binary I just marked the classes as serializable and left it at that. Not good I suspect.
With protobuf-net I need to specify what gets serialized with the [ProtoMember()] attribute. My newbie testing shows that private fields get serialized if so marked as do auto properties.
I do not want to change the class code definitions at all since I still need to be able to deserialize the old persisted data created by the NET serializer. I have a mixture of:
Private fields that get used inside the class
Private fields whose value gets set in constructors
Private fields that are backing fields for non automatic properties
Properties with the backing fields above
Auto properties
Properties with no setters that return some calculation or value determined internally
and probably some others. In other words pretty much every type of field and property.
I guess I need to persist any value that represents the state of the object that cannot be constructed after deserialization from the file.
I suppose there would be no harm in persisting every field and property but that would just make the job slower and the file bigger than it needs to be.
I think I can ignore private fields that are used only inside the class and are not set from outside.
I think I should persist those fields that are set in constructors.
I am not sure about backing fields - is it better to persist them or their public property?
I must persist auto properties
I can't persist properties with no setters so I need to persist whatever fields/properties get used in their calculations.
Am I on the right track or missing the point.
Thanks in advance.
We can't say what needs to be serialized. BinaryFormatter works on an "all fields" basis (unless they are explicitly marked not for serialization). You could use the same approach, but if you're using automatically implemented properties (which is fine) then note that you cannot add attributes to the backing field - unlike field-like events, the following is not valid c#:
[field:ProtoMember(1)] // not valid
public int X { get; set; }
This means that your only sensible choice is to decorate the property:
[ProtoMember(1)]
public int X { get; set; }
Because, if you change the automatically implemented property to a regular property, you will have broken BinaryFormatter's deserialization, since the field-name will have changed. That's fine, though - there's nothing wrong with marking either the fields or the properties (or both in the same type) for serialization. Another consideration on some platforms is accessibility: a private field may be inaccessible, where-as a public field works fine. And obviously public fields are pretty uncommon.
So:
decide what needs to be serialized (I can't tell you this)
mark it for serialization
do not change anything from automatically-implemented property to a regular property if you need BinaryFormatter to keep working (protobuf-net doesn't care if you change this)
Hello I am working on an project in which I should serialize and deserialize my objects to Xml and back to objects. I use the XmlSerializer class in order to achieve this. So my problem is that I can't figure out how to prevent the serialization if the attribute value of an element is invalid. For example I have an element with name person which contain 1 attribute (name)
I would like to prevent the user to put other names than (Alex, Nick,..) in this attribute I need something like xsd restriction (pattern) in this case but for my model. How can I solve this problem?
If you just want conditional serialisation, you can do this with the ShouldSerialize* pattern. So if you have a property Name (for example), you can add:
public bool ShouldSerializeName() {
/* validate; return true to serialize, false to skip */
}
The method needs to be public for XmlSerializer, although the same pattern works in other places (System.ComponentModel, for example) even if no-public.
I'm not sure weather it is a good idea to ignore some data in certain circumstances, but if you really wanna do this, take a look at the IXmlSerializable Interface. I think implementing this interface manually will be the only way to fulfill your requirements.
Basically, the initial problem is I need to make a boolean value serialize as 0 or 1. The solution I found was to implement IXmlSerializable, which I did. Unfortunately the class I'm trying to serialize is generated code off a schema and has an XmlTypeAttribute on it. When I try to (de)serialize the object with the XmlSerializer created in the usual manner ( new XmlSerializer(type)) it throws this exception:
System.InvalidOperationException: Only XmlRoot attribute may be specified for the type ______ Please use XmlSchemaProviderAttribute to specify schema type.
Two options come to mind immediatly:
1) remove the attribute in the generated code.
This change would have to be made every time the code was re-generated.
2) Use an XmlAttributeOverrides object when creating the serializer to remove the attribute. This would require the rest of the code base to "know" that it needs to override that attribute. Also, the exception thrown gives absolutly no clue as to what needs to be done to fix it.
Both options kinda stink. Is there a third option?
I have the same problem, for me removing the IXMLSerializable works, I don't use it, and have you tried to hide the true or false with a some logic in the properties? Like this:
private bool mblnFlag;
public String Flag
{
get
{
return mblnFlag;
}
set
{
mblnFlag = (value == "1")
}
}
Of course you should enhance the properties and do more checking, but that's the idea.
I have a class that is serialized to a XML file. There are several properties that are rarely used but always created. If I delete them within the XML the deserialization still works, because they have the default value.
These unnecessary (bool) attributes make the XML harder to read.
Can I somehow tell C# to omit elements or attributes that still have default value?
Specify the DefaultValueAttribute, and if the value matches, it won't be output.
Rowland has the answer for simple values. For more complex scenarios, you can add a method called public bool ShouldSerializeFoo() (for property Foo) - it it returns false, it won't get serialized.
Use the XMLIgnore() Attribute to mark a property to be ingnored in Serialization / Deserialization.