System.Xml.Serialization.XmlCodeExporter从XSD模式生成代码（以CodeDom代码形式）。但它有一些怪癖。例如一个可选元素：XmlCodeExporter和可空类型
<xs:element name="Something" type="xs:decimal" minOccurs="0" maxOccurs="1"/>
我希望它可以产生Nullable<decimal>类型的相应的编码元件，但它实际上创建decimal类型的成员，然后单独SomethingSpecified字段，它应当单独触发以表示一个空值。这可能是因为该库来自可引用类型的引入之前，但会导致非常不便的代码。
是否有可能调整此代码生成，或者是否有替代工具在这种情况下生成更好的代码？
编辑：我知道我可以修改架构并添加nillable='true'，但我不想更改架构以解决代码生成的限制。
该文章 Writing your own XSD.exe 作者Mike Hadlow给出了创建xsd.exe自己版本的基本框架。它有以下几个步骤：
使用XmlCodeExporter生成要创建的.Net类型和属性。
根据需要调整生成的类型和属性。
在这里，您可能希望删除生成的xxxSpecified属性，并将其相应的“真实”属性提升为空。
使用CSharpCodeProvider生成最终代码。
利用这个框架，并通过使用调试器实验确定由XmlCodeExporter究竟是生成的类型，我创建了以下CustomXsdCodeGenerator：
public class CustomXsdCodeGenerator : CustomXsdCodeGeneratorBase
{
readonly bool promoteToNullable;
public CustomXsdCodeGenerator(string Namespace, bool promoteToNullable) : base(Namespace)
{
this.promoteToNullable = promoteToNullable;
}
protected override void ModifyGeneratedCodeTypeDeclaration(CodeTypeDeclaration codeType, CodeNamespace codeNamespace)
{
RemoveSpecifiedProperties(codeNamespace, promoteToNullable);
base.ModifyGeneratedCodeTypeDeclaration(codeType, codeNamespace);
}
private static void RemoveSpecifiedProperties(CodeNamespace codeNamespace, bool promoteToNullable)
{
foreach (CodeTypeDeclaration codeType in codeNamespace.Types)
{
RemoveSpecifiedProperties(codeType, codeNamespace, promoteToNullable);
}
}
private static void RemoveSpecifiedProperties(CodeTypeDeclaration codeType, CodeNamespace codeNamespace, bool promoteToNullable)
{
var toRemove = new List<CodeTypeMember>();
foreach (var property in codeType.Members.OfType<CodeMemberProperty>())
{
CodeMemberField backingField;
CodeMemberProperty specifiedProperty;
if (!property.TryGetBackingFieldAndSpecifiedProperty(codeType, out backingField, out specifiedProperty))
continue;
var specifiedField = specifiedProperty.GetBackingField(codeType);
if (specifiedField == null)
continue;
toRemove.Add(specifiedProperty);
toRemove.Add(specifiedField);
if (promoteToNullable)
{
// Do not do this for attributes
if (property.CustomAttributes.Cast<CodeAttributeDeclaration>().Any(a => a.AttributeType.BaseType == typeof(System.Xml.Serialization.XmlAttributeAttribute).FullName))
continue;
var typeRef = property.Type;
if (typeRef.ArrayRank > 0)
// An array - not a reference type.
continue;
// OK, two possibilities here:
// 1) The property might reference some system type such as DateTime or decimal
// 2) The property might reference some type being defined such as an enum or struct.
var type = Type.GetType(typeRef.BaseType);
if (type != null)
{
if (!type.IsClass)
{
if (type == typeof(Nullable<>))
// Already nullable
continue;
else if (!type.IsGenericTypeDefinition && (type.IsValueType || type.IsEnum) && Nullable.GetUnderlyingType(type) == null)
{
var nullableType = typeof(Nullable<>).MakeGenericType(type);
var newRefType = new CodeTypeReference(nullableType);
property.Type = newRefType;
backingField.Type = newRefType;
}
}
}
else
{
var generatedType = codeNamespace.FindCodeType(typeRef);
if (generatedType != null)
{
if (generatedType.IsStruct || generatedType.IsEnum)
{
var newRefType = new CodeTypeReference(typeof(Nullable<>).FullName, typeRef);
property.Type = newRefType;
backingField.Type = newRefType;
}
}
}
}
}
foreach (var member in toRemove)
{
codeType.Members.Remove(member);
}
}
}
public static class CodeNamespaceExtensions
{
public static CodeTypeDeclaration FindCodeType(this CodeNamespace codeNamespace, CodeTypeReference reference)
{
if (codeNamespace == null)
throw new ArgumentNullException();
if (reference == null)
return null;
CodeTypeDeclaration foundType = null;
foreach (CodeTypeDeclaration codeType in codeNamespace.Types)
{
if (codeType.Name == reference.BaseType)
{
if (foundType == null)
foundType = codeType;
else if (foundType != codeType)
{
foundType = null;
break;
}
}
}
return foundType;
}
}
public static class CodeMemberPropertyExtensions
{
public static bool TryGetBackingFieldAndSpecifiedProperty(this CodeMemberProperty property, CodeTypeDeclaration codeType,
out CodeMemberField backingField, out CodeMemberProperty specifiedProperty)
{
if (property == null)
{
backingField = null;
specifiedProperty = null;
return false;
}
if ((backingField = property.GetBackingField(codeType)) == null)
{
specifiedProperty = null;
return false;
}
specifiedProperty = null;
var specifiedName = property.Name + "Specified";
foreach (var p in codeType.Members.OfType<CodeMemberProperty>())
{
if (p.Name == specifiedName)
{
// Make sure the property is marked as XmlIgnore (there might be a legitimate, serializable property
// named xxxSpecified).
if (!p.CustomAttributes.Cast<CodeAttributeDeclaration>().Any(a => a.AttributeType.BaseType == typeof(System.Xml.Serialization.XmlIgnoreAttribute).FullName))
continue;
if (specifiedProperty == null)
specifiedProperty = p;
else if (specifiedProperty != p)
{
specifiedProperty = null;
break;
}
}
}
if (specifiedProperty == null)
return false;
if (specifiedProperty.GetBackingField(codeType) == null)
return false;
return true;
}
public static CodeMemberField GetBackingField(this CodeMemberProperty property, CodeTypeDeclaration codeType)
{
if (property == null)
return null;
CodeMemberField returnedField = null;
foreach (var statement in property.GetStatements.OfType<CodeMethodReturnStatement>())
{
var expression = statement.Expression as CodeFieldReferenceExpression;
if (expression == null)
return null;
if (!(expression.TargetObject is CodeThisReferenceExpression))
return null;
var fieldName = expression.FieldName;
foreach (var field in codeType.Members.OfType<CodeMemberField>())
{
if (field.Name == fieldName)
{
if (returnedField == null)
returnedField = field;
else if (returnedField != field)
return null;
}
}
}
return returnedField;
}
}
public abstract class CustomXsdCodeGeneratorBase
{
// This base class adapted from http://mikehadlow.blogspot.com/2007/01/writing-your-own-xsdexe.html
readonly string Namespace;
public CustomXsdCodeGeneratorBase(string Namespace)
{
this.Namespace = Namespace;
}
public void XsdToClassTest(IEnumerable<string> xsds, TextWriter codeWriter)
{
XsdToClassTest(xsds.Select(xsd => (Func<TextReader>)(() => new StringReader(xsd))), codeWriter);
}
public void XsdToClassTest(IEnumerable<Func<TextReader>> xsds, TextWriter codeWriter)
{
var schemas = new XmlSchemas();
foreach (var getReader in xsds)
{
using (var reader = getReader())
{
var xsd = XmlSchema.Read(reader, null);
schemas.Add(xsd);
}
}
schemas.Compile(null, true);
var schemaImporter = new XmlSchemaImporter(schemas);
var maps = new List<XmlTypeMapping>();
foreach (XmlSchema xsd in schemas)
{
foreach (XmlSchemaType schemaType in xsd.SchemaTypes.Values)
{
maps.Add(schemaImporter.ImportSchemaType(schemaType.QualifiedName));
}
foreach (XmlSchemaElement schemaElement in xsd.Elements.Values)
{
maps.Add(schemaImporter.ImportTypeMapping(schemaElement.QualifiedName));
}
}
// create the codedom
var codeNamespace = new CodeNamespace(this.Namespace);
var codeExporter = new XmlCodeExporter(codeNamespace);
foreach (XmlTypeMapping map in maps)
{
codeExporter.ExportTypeMapping(map);
}
ModifyGeneratedNamespace(codeNamespace);
// Check for invalid characters in identifiers
CodeGenerator.ValidateIdentifiers(codeNamespace);
// output the C# code
var codeProvider = new CSharpCodeProvider();
codeProvider.GenerateCodeFromNamespace(codeNamespace, codeWriter, new CodeGeneratorOptions());
}
protected virtual void ModifyGeneratedNamespace(CodeNamespace codeNamespace)
{
foreach (CodeTypeDeclaration codeType in codeNamespace.Types)
{
ModifyGeneratedCodeTypeDeclaration(codeType, codeNamespace);
}
}
protected virtual void ModifyGeneratedCodeTypeDeclaration(CodeTypeDeclaration codeType, CodeNamespace codeNamespace)
{
}
}
为了测试它，我创建了以下几种类型：
namespace SampleClasses
{
public class SimleSampleClass
{
[XmlElement]
public decimal Something { get; set; }
[XmlIgnore]
public bool SomethingSpecified { get; set; }
}
[XmlRoot("RootClass")]
public class RootClass
{
[XmlArray]
[XmlArrayItem("SampleClass")]
public List<SampleClass> SampleClasses { get; set; }
}
[XmlRoot("SampleClass")]
public class SampleClass
{
[XmlAttribute]
public long Id { get; set; }
public decimal Something { get; set; }
[XmlIgnore]
public bool SomethingSpecified { get; set; }
public SomeEnum SomeEnum { get; set; }
[XmlIgnore]
public bool SomeEnumSpecified { get; set; }
public string SomeString { get; set; }
[XmlIgnore]
public bool SomeStringSpecified { get; set; }
public decimal? SomeNullable { get; set; }
[XmlIgnore]
public bool SomeNullableSpecified { get; set; }
public DateTime SomeDateTime { get; set; }
[XmlIgnore]
public bool SomeDateTimeSpecified { get; set; }
// https://stackoverflow.com/questions/3280362/most-elegant-xml-serialization-of-color-structure
[XmlElement(Type = typeof(XmlColor))]
public Color MyColor { get; set; }
[XmlIgnore]
public bool MyColorSpecified { get; set; }
}
public enum SomeEnum
{
DefaultValue,
FirstValue,
SecondValue,
ThirdValue,
}
// https://stackoverflow.com/questions/3280362/most-elegant-xml-serialization-of-color-structure
public struct XmlColor
{
private Color? color_;
private Color Color
{
get
{
return color_ ?? Color.Black;
}
set
{
color_ = value;
}
}
public XmlColor(Color c) { color_ = c; }
public Color ToColor()
{
return Color;
}
public void FromColor(Color c)
{
Color = c;
}
public static implicit operator Color(XmlColor x)
{
return x.ToColor();
}
public static implicit operator XmlColor(Color c)
{
return new XmlColor(c);
}
[XmlAttribute]
public string Web
{
get { return ColorTranslator.ToHtml(Color); }
set
{
try
{
if (Alpha == 0xFF) // preserve named color value if possible
Color = ColorTranslator.FromHtml(value);
else
Color = Color.FromArgb(Alpha, ColorTranslator.FromHtml(value));
}
catch (Exception)
{
Color = Color.Black;
}
}
}
[XmlAttribute]
public byte Alpha
{
get { return Color.A; }
set
{
if (value != Color.A) // avoid hammering named color if no alpha change
Color = Color.FromArgb(value, Color);
}
}
public bool ShouldSerializeAlpha() { return Alpha < 0xFF; }
}
}
使用泛型xsd.exe我从它们生成了以下模式：
<xs:schema elementFormDefault="qualified" xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="SimleSampleClass" nillable="true" type="SimleSampleClass" />
<xs:complexType name="SimleSampleClass">
<xs:sequence>
<xs:element minOccurs="0" maxOccurs="1" name="Something" type="xs:decimal" />
</xs:sequence>
</xs:complexType>
<xs:element name="RootClass" nillable="true" type="RootClass" />
<xs:complexType name="RootClass">
<xs:sequence>
<xs:element minOccurs="0" maxOccurs="1" name="SampleClasses" type="ArrayOfSampleClass" />
</xs:sequence>
</xs:complexType>
<xs:complexType name="ArrayOfSampleClass">
<xs:sequence>
<xs:element minOccurs="0" maxOccurs="unbounded" name="SampleClass" nillable="true" type="SampleClass" />
</xs:sequence>
</xs:complexType>
<xs:complexType name="SampleClass">
<xs:sequence>
<xs:element minOccurs="0" maxOccurs="1" name="Something" type="xs:decimal" />
<xs:element minOccurs="0" maxOccurs="1" name="SomeEnum" type="SomeEnum" />
<xs:element minOccurs="0" maxOccurs="1" name="SomeString" type="xs:string" />
<xs:element minOccurs="0" maxOccurs="1" name="SomeNullable" nillable="true" type="xs:decimal" />
<xs:element minOccurs="0" maxOccurs="1" name="SomeDateTime" type="xs:dateTime" />
<xs:element minOccurs="0" maxOccurs="1" name="MyColor" type="XmlColor" />
</xs:sequence>
<xs:attribute name="Id" type="xs:long" use="required" />
</xs:complexType>
<xs:simpleType name="SomeEnum">
<xs:restriction base="xs:string">
<xs:enumeration value="DefaultValue" />
<xs:enumeration value="FirstValue" />
<xs:enumeration value="SecondValue" />
<xs:enumeration value="ThirdValue" />
</xs:restriction>
</xs:simpleType>
<xs:complexType name="XmlColor">
<xs:attribute name="Web" type="xs:string" />
<xs:attribute name="Alpha" type="xs:unsignedByte" />
</xs:complexType>
<xs:element name="SampleClass" nillable="true" type="SampleClass" />
<xs:element name="SomeEnum" type="SomeEnum" />
<xs:element name="XmlColor" type="XmlColor" />
</xs:schema>
而且，采用这种模式，我再生利用CustomXsdCodeGenerator下面的C＃类与promoteToNullable = true和Namespace = "Question42295155"：
namespace Question42295155 {
/// <remarks/>
[System.CodeDom.Compiler.GeneratedCodeAttribute("XsdToClassTest", "1.0.0.0")]
[System.SerializableAttribute()]
[System.Diagnostics.DebuggerStepThroughAttribute()]
[System.ComponentModel.DesignerCategoryAttribute("code")]
[System.Xml.Serialization.XmlRootAttribute(Namespace="", IsNullable=true)]
public partial class SimleSampleClass {
private System.Nullable<decimal> somethingField;
/// <remarks/>
public System.Nullable<decimal> Something {
get {
return this.somethingField;
}
set {
this.somethingField = value;
}
}
}
/// <remarks/>
[System.CodeDom.Compiler.GeneratedCodeAttribute("XsdToClassTest", "1.0.0.0")]
[System.SerializableAttribute()]
[System.Diagnostics.DebuggerStepThroughAttribute()]
[System.ComponentModel.DesignerCategoryAttribute("code")]
[System.Xml.Serialization.XmlRootAttribute(Namespace="", IsNullable=true)]
public partial class SampleClass {
private System.Nullable<decimal> somethingField;
private System.Nullable<SomeEnum> someEnumField;
private string someStringField;
private System.Nullable<decimal> someNullableField;
private System.Nullable<System.DateTime> someDateTimeField;
private XmlColor myColorField;
private long idField;
/// <remarks/>
public System.Nullable<decimal> Something {
get {
return this.somethingField;
}
set {
this.somethingField = value;
}
}
/// <remarks/>
public System.Nullable<SomeEnum> SomeEnum {
get {
return this.someEnumField;
}
set {
this.someEnumField = value;
}
}
/// <remarks/>
public string SomeString {
get {
return this.someStringField;
}
set {
this.someStringField = value;
}
}
/// <remarks/>
[System.Xml.Serialization.XmlElementAttribute(IsNullable=true)]
public System.Nullable<decimal> SomeNullable {
get {
return this.someNullableField;
}
set {
this.someNullableField = value;
}
}
/// <remarks/>
public System.Nullable<System.DateTime> SomeDateTime {
get {
return this.someDateTimeField;
}
set {
this.someDateTimeField = value;
}
}
/// <remarks/>
public XmlColor MyColor {
get {
return this.myColorField;
}
set {
this.myColorField = value;
}
}
/// <remarks/>
[System.Xml.Serialization.XmlAttributeAttribute()]
public long Id {
get {
return this.idField;
}
set {
this.idField = value;
}
}
}
/// <remarks/>
[System.CodeDom.Compiler.GeneratedCodeAttribute("XsdToClassTest", "1.0.0.0")]
[System.SerializableAttribute()]
[System.Xml.Serialization.XmlRootAttribute(Namespace="", IsNullable=false)]
public enum SomeEnum {
/// <remarks/>
DefaultValue,
/// <remarks/>
FirstValue,
/// <remarks/>
SecondValue,
/// <remarks/>
ThirdValue,
}
/// <remarks/>
[System.CodeDom.Compiler.GeneratedCodeAttribute("XsdToClassTest", "1.0.0.0")]
[System.SerializableAttribute()]
[System.Diagnostics.DebuggerStepThroughAttribute()]
[System.ComponentModel.DesignerCategoryAttribute("code")]
[System.Xml.Serialization.XmlRootAttribute(Namespace="", IsNullable=true)]
public partial class XmlColor {
private string webField;
private byte alphaField;
/// <remarks/>
[System.Xml.Serialization.XmlAttributeAttribute()]
public string Web {
get {
return this.webField;
}
set {
this.webField = value;
}
}
/// <remarks/>
[System.Xml.Serialization.XmlAttributeAttribute()]
public byte Alpha {
get {
return this.alphaField;
}
set {
this.alphaField = value;
}
}
}
/// <remarks/>
[System.CodeDom.Compiler.GeneratedCodeAttribute("XsdToClassTest", "1.0.0.0")]
[System.SerializableAttribute()]
[System.Diagnostics.DebuggerStepThroughAttribute()]
[System.ComponentModel.DesignerCategoryAttribute("code")]
[System.Xml.Serialization.XmlRootAttribute(Namespace="", IsNullable=true)]
public partial class RootClass {
private SampleClass[] sampleClassesField;
/// <remarks/>
public SampleClass[] SampleClasses {
get {
return this.sampleClassesField;
}
set {
this.sampleClassesField = value;
}
}
}
/// <remarks/>
[System.CodeDom.Compiler.GeneratedCodeAttribute("XsdToClassTest", "1.0.0.0")]
[System.SerializableAttribute()]
[System.Diagnostics.DebuggerStepThroughAttribute()]
[System.ComponentModel.DesignerCategoryAttribute("code")]
[System.Xml.Serialization.XmlRootAttribute(Namespace="", IsNullable=true)]
public partial class ArrayOfSampleClass {
private SampleClass[] sampleClassField;
/// <remarks/>
[System.Xml.Serialization.XmlElementAttribute("SampleClass", IsNullable=true)]
public SampleClass[] SampleClass {
get {
return this.sampleClassField;
}
set {
this.sampleClassField = value;
}
}
}
}
注意：
有在名称结尾没有属性Specified。
属性Something,SomeEnum和SomeDateTime已成为空值。
已经为空的public decimal? SomeNullable { get; set; }往返public System.Nullable<decimal> SomeNullable，而不是成为一些可怕的双可空System.Nullable<System.Nullable<decimal>>的失败。
我然后产生从最初RootClass以下XML：
<RootClass xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<SampleClasses>
<SampleClass Id="10101">
<Something>2.718</Something>
<SomeEnum>ThirdValue</SomeEnum>
<SomeString>hello</SomeString>
<SomeNullable>3.14</SomeNullable>
<SomeDateTime>2017-02-28T00:00:00-05:00</SomeDateTime>
<MyColor Web="Maroon" />
</SampleClass>
</SampleClasses>
</RootClass>
，并能够成功地反序列化它的产生Question42295155.RootClass课，而不会丢失数据。
注 - 此代码是轻微测试。如果您想提供一个样本模式，我可以重新测试一下。请参阅Code Generation in the .NET Framework Using XML Schema。
尝试使用Xsd2Code工具。我广泛使用它而不是xsd.exe。不幸的是，我不能确定你提到的具体问题是否解决了。 – Evk
您是否尝试过使用'nillable ='true''而不是最小/最大值？ – tchrikch
@Evk：Xsd2Code似乎在底层使用了XmlCodeExporter，似乎也有相同的问题。 – JacquesB