xs:choice
In This Topic
Sample Schema
Consider the following schema, Root must contain one of the child nodes A,B,C or D.
| Choice.xsd |
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<?xml version="1.0" encoding="utf-8" ?> <!--Created with Liquid Studio 2018 (https://www.liquid-technologies.com)--> <xs:schema elementFormDefault="qualified" targetNamespace="http://www.liquid-technologies.com/sample/choice" xmlns:xs="http://www.w3.org/2001/XMLSchema"> <xs:element name="Root"> <xs:complexType> <xs:choice> <xs:element name="A" type="xs:string" /> <xs:element name="B" type="xs:int" /> <xs:element name="C"> <xs:complexType> <xs:sequence> <xs:element name="Child" type="xs:string" /> </xs:sequence> </xs:complexType> </xs:element> <xs:element name="D" type="xs:int" minOccurs="0" maxOccurs="unbounded" /> </xs:choice> </xs:complexType> </xs:element> </xs:schema> |
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D's cardinality is 0-n, so zero D's is an acceptable value for Root. In other words its valid for Root to be empty.
Generated Code
The following code is generated for the choice.
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public partial class RootElm
{
public RootChc Chc { get; set; } = new RootChc();
public partial class RootChc
{
public System.String A { get; set; }
public System.Int32? B { get; set; }
public CElm C { get; set; }
public List<System.Int32> D { get; } = new List<System.Int32>();
}
public partial class CElm
{
public CSeq Seq { get; set; } = new CSeq();
public partial class CSeq
{
public System.String Child { get; set; } = "";
}
}
}
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The Lx... attributes, qualifying namespaces and comments have been removed for clarity.
The class RootChc represents the xs:choice, so only one of the properties in RootChc can be set.
Also note that all properties within the RootChc class are represented in their optional form (as its a choice all but one of the options should be empty).
- A is considered to have a value if its not null (even if its empty)
- B is considered to have a value if its not null (Nullable.HasValue = true)
- C is considered to have a value if its not null
- D is considered to have a valid if the collection is not empty
Also see Cardinality
Writing Sample Code
We can use the following code to build instances of the Root Element
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LxSerializer<RootElm> serializer = new LxSerializer<RootElm>(); LxWriterSettings writerSettings = new LxWriterSettings(); writerSettings.ErrorHandler = WriterErrorHandler; RootElm elmWithA = new RootElm(); elmWithA.Chc.A = "test"; serializer.Serialize(@"..\..\ChoiceA_Output.xml", elmWithA, writerSettings); // OK RootElm elmWithD = new RootElm(); elmWithD.Chc.D.Add(1); elmWithD.Chc.D.Add(2); serializer.Serialize(@"..\..\ChoiceD_Output.xml", elmWithD, writerSettings); // OK RootElm elmWithAB = new RootElm(); elmWithAB.Chc.A = "test"; elmWithAB.Chc.B = 2; serializer.Serialize(@"..\..\ChoiceAB_Output.xml", elmWithAB, writerSettings); // Error via WriterErrorHandler : 2 choice populated |
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| Error Handler Code |
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public static void WriterErrorHandler(string msg, LxErrorSeverity severity, LxErrorCode errorCode, object targetObject) { Console.WriteLine($"{severity} : {errorCode} : {msg}"); } |
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Sample Output
Output : ChoiceA_Output.xml
| ChoiceA_Output.xml |
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<?xml version="1.0" encoding="utf-8"?> <Root xmlns="http://www.liquid-technologies.com/sample/choice"> <A>test</A> </Root> |
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Output : ChoiceD_Output.xml
| ChoiceD_Output.xml |
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<?xml version="1.0" encoding="utf-8"?> <Root xmlns="http://www.liquid-technologies.com/sample/choice"> <D>1</D> <D>2</D> </Root> |
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Output : ChoiceAB_Output.xml
| ChoiceAB_Output.xml |
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<?xml version="1.0" encoding="utf-8"?> <Root xmlns="http://www.liquid-technologies.com/sample/choice"> <A>test</A> <B>2</B> </Root> |
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| Error Output |
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Error : ExtraChoiceValues : A choice may only contain 1 value. The object /Root contains more than one option. |
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When the sample runs an error is raised, if the error handler allows the serialization to continue (i.e. does not throw an exception), then the serializer will write out all the options in the object model. In this sample, Root now contains 2 child elements A and B, which makes it invalid.
Reading Sample Code
The following code will read back in the files created above.
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LxSerializer<RootElm> serializer = new LxSerializer<RootElm>(); LxReaderSettings readerSettings = new LxReaderSettings(); readerSettings.ErrorHandler = ReaderErrorHandler; RootElm elmWithA = serializer.Deserialize(@"..\..\ChoiceA_Output.xml", readerSettings); // OK Debug.Assert(elmWithA.Chc.A == "test"); RootElm elmWithD = serializer.Deserialize(@"..\..\ChoiceD_Output.xml", readerSettings); // OK Debug.Assert(elmWithD.Chc.D.Count == 2); Debug.Assert(elmWithD.Chc.D[0] == 1); Debug.Assert(elmWithD.Chc.D[1] == 2); RootElm elmWithAB = serializer.Deserialize(@"..\..\ChoiceAB_Output.xml", readerSettings); // Error via ReaderErrorHandler : 2 choice populated Debug.Assert(elmWithAB.Chc.A == "test"); Debug.Assert(elmWithAB.Chc.D.Count == 0); |
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| Error Handler Code |
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public static void ReaderErrorHandler(string msg, LxErrorSeverity severity, LxErrorCode errorCode, TextLocation location, object targetObject) { Console.WriteLine($"{severity} : {errorCode} : {location} : {msg}"); } |
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When the valid XML files ChoiceA_Output.xml and ChoiceD_Output.xml are read they produce an object model identical to the one serialized out in the code above.
However when the invalid XML file ChoiceAB_Output.xml is read an 'UnknownElement' error is raised, and additional element B is discarded.
| Error Output |
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Error : UnknownElement : 4:11 : No suitable type could be found to process the element B. |
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It is possible to retain the child element B within the model value by setting the 'Handle unknown nodes', see Unexpected Elements for more details.
See Also