The following questions are about XML serialization/deserialization and schema validation for a .net library of types which are to be used for data exchange.
First question, if I have a custom xml namespace say "http://mydomain/mynamespace" do I have to add a
[XmlRoot(Namespace = "http://mydomain/mynamespace")]
to every class in my library. Or is there a way to define this namespace as default for the whole assembly?
Second question, is there a reason behind the always added namespaces
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"
even if there is no actual reference to any of the namespaces? I just feel they add noise to the resulting xml. Is there a way to remove them an only have the custom namespace in the resulting xml?
Third question, are there tools to support the generation of schema definitions (e.g. for all public [Serializable] classes of an assembly) and the validation of xml against specific schemas available?
If there are, would you recommend XML Schema from W3C or RELAX NG?
Just to add - the "xsi" etc is there to support things like xsi:nil on values later on - a well-known pattern for nullable values. It has to write the stream "forwards only", and it doesn't know (when it writes the first bit) whether it will need nil or not, so it assumes that writing it unnecessarily once is better than having to use the full namespace potentially lots of times.
1) XmlRoot can only be set at the class/struct/interface level (or on return values). So you can't use it on the assembly level. What you're looking for is the XmlnsDefinitionAttribute, but I believe that only is used by the XamlWriter.
2) If you're worried about clutter you should avoid xml. Well formed xml is full of clutter. I believe there are ways to interract with the xml produced by the serializer, but not directly with the XmlSerializer. You have much more control over the XML produced with the XmlWriter class. Check here for how you can use the XmlWriter to handle namespaces.
3) XSD.exe can be used to generate schemas for POCOs, I believe (I've always written them by hand; I may be using this soon to write up LOTS, tho!).
Tools,
- xsd.exe, with a command line like
xsd /c /n:myNamespace.Schema.v2_0 myschema_v2_0.xsd
I put the schema in a separate project.
liqudXML which is useful if there are several schemas, or you want full support of the schema features (DateTimes with offsets, positive/Negative decimals,), and cross platform generation.
Related
I am trying develop a website which provide user interface to generate XML file. The user interface will ask for data required in various XML elements. The generate XML should follow DTD specifications.
So here is what I did.
I converted DTD to XSD.
I created C# class using xsd.exe tool.
Now my question is how can I generate dynamic input boxes on the webpage that will ask for required element data from the C# class I created.
I need some way to know the required and optional elements and their data type and attribute and all from the C# class I created.
i hope you get what i am asking, thanks for looking.
Keep in mind that most of the required/optional semantics from the xsd are lost in the classes generated with xsd.exe. You basically have 2 (+1 edited later ) options:
Use reflection over your generated types to render UI elements for each property. You'll have to manually manage/define databindings
Drop the xsd.exe classes and generate your UI elements by traversing the xsd itself. That way you get way more info about optional/nullable elements, cardinality etc. Construct your resulting xml by hand (use XDocument) from your UI inputs.
The hybrid approach: Reflect over generated classes for structure (easier traversal logic. no need to handle external includes etc). Go to the xsd for the additional info (You'll need to somehow figure out where in the xsd to find your needed definitions that map to the current property)
Either way you choose this will not be a trivial task and you'll need a lot of work to make it happen. And if we're going in the realm of XSD choice elements etc. you'll soon figure out that no straight forward UI can cover all the possible scenarios
I've been given the task of writing a complex XML file (I do have the XML schema, XSD) in C#, which has the possibility of being quite large depending on the situation. I'd like to implement streaming since the file can be large, so it looks like the best option is to use the XMLWriter. Before I go down the path of extending the XMLWriter class and writing a bunch of custom code, I was wondering if it was possible to, somehow, leverage the XML schema I have? I know I can convert my schema to C# objects using the XML Schema Definition Tool in Visual Studio, but I don't know if this is something I can use with the XMLWriter. I've converted an XML schema to C# objects and serialized them using XMLSerializer in the past, but not with the XMLWriter.
See Generating XML Documents from XML Schemas
http://msdn.microsoft.com/en-us/library/aa302296.aspx
Summary: Priya Lakshminarayanan shows how you can use the classes in the System.XML.Schema namespace of the Microsoft .NET Framework to build a tool that generates sample XML documents that conform to a given schema.
In the Visual Studio Schema Explorer you are able to generate an instance document from any element definition in your Schema. This article exposes the underlying code that makes that happen. I should note that Altova's XMLSpy has a more flexible tool for generating instances from the Schema, allowing you to set various parameters about the depth, repetition, and generated text values.
I used the XMLGenerator code included in the article to create a class that generates new XML document instances from my Schema for the 20 types of documents that we define. I added hints in my Schema as attributes in my own namespace to help the XMLGenerator generate a minimal valid document with some default text to help the users get started with the new document. So there is a lot you can do with the XmlGenerator.
I have a requirement like i need to write an entity class in C# which can hold xml data.
I want to avoid overhead of checking the well-formedness of saved xml.
I have a corresponding column with type XML. Do we have xml data type or some class which can be used as a class field to hold xml.
Thanks in advance
Update: The service using this Entity class is WCF service and in future we are making it REST compatible. Will XmlDocument or XElement work with it?
There are a number of ways, two of which are string and XmlDocument.
string would be 'easier' for fragments and not-well-formed XML, but XmlDocument can be configured with options to allow fragments; you'll have more trouble with ill-formed data though.
if you describe your object in a XSD file you can get a compiler to generate all your C# classes automatically and easily regenerate them when you make changes.
This makes XML / C# a breeze. You can go to other languages too using equivilent generators.
See the tools described here: XSDObjectGen.exe vs XSD.exe
I believe the XSD.exe tool will read in example XML and do most of the work of producing an XSD which you can refine.
If you don't need support for a fixed XML/XSD format file why can't you make any class serialize to XML by using the [Serializable] class attribute and .Net APIS to serialize/deserialize?
I have a XSD file, from which I want to generate C# and Java classes as well.
I first set the namespace in the XSD according to my C# namespace where my classes resides. The generation (with the Microsoft tools) works fine and also the serialisation works great and I can validat them against the XSD - perfect.
Now I want to create java classes with JAXB.
The problem is that the classes which are going to be created have a different package structure then the one in C#. So when I set the XSD namespace to the package structure of java, it works fine. I can serialize and validate the XML.
Now my question(s):
Is there a way to solve this? (Have one XSD for both generation tools)
Do I lack a understanding of what the namespace actually is needed for?
Thank you
Edit: Since it seems to be that there is a missunderstanding, I added an example
XSD: targetNamespace = "http://foo.bar/mySubNs/model"
C# Modelnamespace: com.foo.mySubNs.model (which fits the XSD namespace)
all generated classes will have the same namespace provided though the MS codegen
Java Modelnamespace : com.foo.myOtherSubNs.model (which differs from the XSD namespace)
the generated classes will have the "C# namespace". As a result the classes will not compile.
If I would change the namespace during the code generation for java, I can compile the classes. So far so good. But I won't be able to validate the generated XML by that java classes against the XSD, since the namespace differs.
To marshall my objects in Java, I use JAXB like this:
ValidationEventCollector validationCollector = new ValidationEventCollector();
SchemaFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
Schema schema = schemaFactory.newSchema(new File ("my/schema/location"));
// JAXB_CONTEXT is just an instance of "JAXBContext"
Marshaller marshaller = JAXB_CONTEXT.createMarshaller();
marshaller.setSchema(schema);
marshaller.setEventHandler(validationCollector);
marshaller.setProperty(Marshaller.JAXB_ENCODING, "UTF-8");
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE);
JAXBElement<MyClass> root = new JAXBElement<MyClass> ( new QName(MyClass.class.getPackage().getName(),"MyClass"),MyClass.class, node);
marshaller.marshal(root, new File("output/Path/obj.xml"));
To build my java classes from the schema I use a xjc-task in an ant build script:
<xjc destdir="${dir.src.gen}" removeOldOutput="no" extension="true">
<schema dir="${dir.schema}" includes="${file.schema}"/>
<binding dir="${dir.schema}" includes="*.xjb"/>
<produces dir="${dir.src.gen}" includes="**/*.java"/>
</xjc>
The XSD namespace doesn't have to match the package structure, at least not in Java. When generating the classes using JAXB just provide the package you want to put the classes into.
You must take your pick as to what model is the main one: XSD, C#, or Java code. Once you make that choice, you must let the other two vary as they may. The best choice would be to make your XSD the reference model, generate the code in both languages with their respective tools, and just accept the results.
You can also try to pick the XML namespace such that the code at both ends will be satisfactory, but don't try to force anything to the last letter. That's not how it's meant to work.
I'm using DataContractSerializer to serialize a class with DataContract and DataMember attributes to an XML file. My class could potentially change later, and thus the format of the serialized files could also change. I'd like to tag the files I'm saving with a version number so I at least know what version each file is from. I'm still deciding how and if I want to add functionality that will migrate files in older formats to later formats. But right now I'd be happy with just identifying a version mismatch.
Is the namespace of the XML file the correct place to store the version of the file? I was thinking of attributing my class with a DataContract attributes as follows.
[DataContract(Name="MyClass",Namespace="http://www.mycompany.com/MyProject/1.0
public class MyClass
...
Then later if MyClass changes I would change the namespace...
[DataContract(Name="MyClass",Namespace="http://www.mycompany.com/MyProject/2.0)]
public class MyClass
...
Is this the correct usage of XML namespaces, or is there another more prefered way to save the version of an XML file?
You can do it this way, but then the XML representation of your data becomes completely different from version to version from XML Infoset point of view (in which namespace is the part of the qualified name of the element), so you have neither backwards nor forwards compatibility.
Now, one advantage XML has is that it can be easily processed in a forward-compatible way with technologies such as XPath and XSLT - you just pick the elements you can interpret, and leave anything you don't recognize as is. But this requires elements with the same meaning to retain the same name (including namespace) between versions.
In general, it is best to make your schemas forward-compatible. If you can't achieve that, you might still want to provide as much compatibility as possible with existing tools (it is often easier to achieve compatibility against tools which only read data, rather than with those which also write it). Consequently, you avoid storing version number in such cases, and just try to parse whatever you're given, signalling an error if the input is definitely malformed.
If you come to the point where you absolutely must break compatibility in both directions and start from a clean slate, the suggested way of handling this for WCF data contracts is indeed by changing the namespace, as described in best practices on data contract versioning. There are a few minor variations there as well, such as using publication date instead of version number in the URL (W3C is quite fond of this for their schemas), but these are mostly stylistic.