我的WCF4 Rest Service及Entity Framework with POCO之旅（四）——定制Entity
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http://www.cnblogs.com/Gildor/archive/2011/04/20/2022013.html
我的WCF4 Rest Service及Entity Framework with POCO之旅（四）——定制Entity
本文将focus几个结合使用WCF REST和Entity Framework with POCO的常见问题。
Entity Type和Property名称的大小写
按照RESTful的习惯，XML或者JSON格式的数据的node名称开头字母一般使用小写，比如，下面是一段Google Buzz API的RESTful返回信息：
<entry xmlns="http://www.w3.org/2005/Atom" xmlns:activity="http://activitystrea.ms/spec/1.0"> <id>tag:google.com,2010:buzz:z12puk22ajfyzsz</id> <author> <name>Ted Taco</name> <uri>http://www.google.com/profiles/ted</uri> </author> <published>2010-04-23T11:03:34.342Z</published> <updated>2010-04-23T11:03:34.342Z</updated> <activity:object> <activity:object-type>http://activitystrea.ms/schema/1.0/note</activity:object-type> <content type="html">Hey, this is my first Buzz Post!</content> <activity:object> <link rel="alternate" type="text/html" href="http://www.google.com/buzz/ted/Hey-this-is-my-first-Buzz-Post" /> <!-- more data --></entry>要让我们的Service返回数据node也使用小写字母开头，我们需要给Entity加上[DataContract]和[DataMember] attributes。（当然也可以修改WCF的behavior让它使用我们提供的的serializer但是现在框架既然还能满足需求，我还不想那么做。）
手动加attribute显然不是一个好主意，而且可以想见一旦模型代码重新生成，我们的修改就都没了。我们需要修改生成Entity的T4模板(Model.tt和Model.Context.tt)。
T4模板和其他的一些代码生成器的模板很相似，和现在的ASP.NET也有点相似。主要特点就是在模板内容（对于模板来说类似于纯文本）中嵌入C#代码。
由于T4模板的可读性不是很好，而VS原生又不支持T4的高亮和intellisense，开始编辑之前，最好装一个支持T4高亮的插件。我用的是Visual T4，虽然反应比较慢还有一些bug，不过是免费的，基本也够用了。
我们先看一下现在的Model.tt的全貌：
<#@ template language="C#" debug="false" hostspecific="true"#><#@ include file="EF.Utility.CS.ttinclude"#><#@ output extension=".cs"#><#CodeGenerationTools code = new CodeGenerationTools(this);MetadataLoader loader = new MetadataLoader(this);CodeRegion region = new CodeRegion(this, 1);MetadataTools ef = new MetadataTools(this);string inputFile = @"WcfRestServiceDemo.edmx";EdmItemCollection ItemCollection = loader.CreateEdmItemCollection(inputFile);string namespaceName = code.VsNamespaceSuggestion();EntityFrameworkTemplateFileManager fileManager = EntityFrameworkTemplateFileManager.Create(this);// Write out support code to primary template output fileWriteHeader(fileManager);BeginNamespace(namespaceName, code);WriteCustomObservableCollection();EndNamespace(namespaceName);// Emit Entity Typesforeach (EntityType entity in ItemCollection.GetItems<EntityType>().OrderBy(e => e.Name)){ fileManager.StartNewFile(entity.Name + ".cs"); BeginNamespace(namespaceName, code); bool entityHasNullableFKs = entity.NavigationProperties.Any(np => np.GetDependentProperties().Any(p=>ef.IsNullable(p)));#><#=Accessibility.ForType(entity)#> <#=code.SpaceAfter(code.AbstractOption(entity))#>partial class <#=code.Escape(entity)#><#=code.StringBefore(" : ", code.Escape(entity.BaseType))#>{<# region.Begin("Primitive Properties"); foreach (EdmProperty edmProperty in entity.Properties.Where(p => p.TypeUsage.EdmType is PrimitiveType && p.DeclaringType == entity)) { bool isForeignKey = entity.NavigationProperties.Any(np=>np.GetDependentProperties().Contains(edmProperty)); bool isDefaultValueDefinedInModel = (edmProperty.DefaultValue != null); bool generateAutomaticProperty = false;#> <#=PropertyVirtualModifier(Accessibility.ForProperty(edmProperty))#> <#=code.Escape(edmProperty.TypeUsage)#> <#=code.Escape(edmProperty)#> {<# if (isForeignKey) {#> <#=code.SpaceAfter(Accessibility.ForGetter(edmProperty))#>get { return <#=code.FieldName(edmProperty)#>; } <#=code.SpaceAfter(Accessibility.ForSetter(edmProperty))#>set {<# if (entityHasNullableFKs) {#> try { _settingFK = true;<# PushIndent(CodeRegion.GetIndent(1)); } if (((PrimitiveType)edmProperty.TypeUsage.EdmType).PrimitiveTypeKind == PrimitiveTypeKind.Binary) {#> if (!StructuralComparisons.StructuralEqualityComparer.Equals(<#=code.FieldName(edmProperty)#>, value))<# } else {#> if (<#=code.FieldName(edmProperty)#> != value)<# }#> {<# foreach (var np in entity.NavigationProperties.Where(np=>np.GetDependentProperties().Contains(edmProperty))) { EdmProperty principalProperty = ef.GetCorrespondingPrincipalProperty(np, edmProperty); if (((PrimitiveType)principalProperty.TypeUsage.EdmType).PrimitiveTypeKind == PrimitiveTypeKind.Binary) {#> if ((<#=code.Escape(np)#> != null) && !StructuralComparisons.StructuralEqualityComparer.Equals(<#=code.Escape(np)#>.<#=code.Escape(principalProperty)#>, value))<# } else {#> if (<#=code.Escape(np)#> != null && <#=code.Escape(np)#>.<#=code.Escape(principalProperty)#> != value)<# }#> {<# if (!(np.GetDependentProperties().Where(p=>ef.IsNullable(p)).Any() && np.GetDependentProperties().Count() > 1)) {#> <#=code.Escape(np)#> = null;<# } else {#> var previousValue = <#=code.FieldName(np)#>; <#=code.FieldName(np)#> = null; Fixup<#=np.Name#>(previousValue, skipKeys: true);<# }#> }<# }#> <#=code.FieldName(edmProperty)#> = value; }<# if (entityHasNullableFKs) { PopIndent();#> } finally { _settingFK = false; }<# }#> }<# } else if (isDefaultValueDefinedInModel) {#> <#=code.SpaceAfter(Accessibility.ForGetter(edmProperty))#>get { return <#=code.FieldName(edmProperty)#>; } <#=code.SpaceAfter(Accessibility.ForSetter(edmProperty))#>set { <#=code.FieldName(edmProperty)#> = value; }<# } else { generateAutomaticProperty = true;#> <#=code.SpaceAfter(Accessibility.ForGetter(edmProperty))#>get; <#=code.SpaceAfter(Accessibility.ForSetter(edmProperty))#>set;<# }#> }<# if (!generateAutomaticProperty) {#> private <#=code.Escape(edmProperty.TypeUsage)#> <#=code.FieldName(edmProperty)#><#=code.StringBefore(" = ", code.CreateLiteral(edmProperty.DefaultValue))#>;<# } } region.End(); region.Begin("Complex Properties"); foreach(EdmProperty edmProperty in entity.Properties.Where(p => p.TypeUsage.EdmType is ComplexType && p.DeclaringType == entity)) {#> <#=PropertyVirtualModifier(Accessibility.ForProperty(edmProperty))#> <#=code.Escape(edmProperty.TypeUsage)#> <#=code.Escape(edmProperty)#> { <#=code.SpaceAfter(Accessibility.ForGetter(edmProperty))#>get { return <#=code.FieldName(edmProperty)#>; } <#=code.SpaceAfter(Accessibility.ForSetter(edmProperty))#>set { <#=code.FieldName(edmProperty)#> = value; } } private <#=code.Escape(edmProperty.TypeUsage)#> <#=code.FieldName(edmProperty)#> = new <#=code.Escape(edmProperty.TypeUsage)#>();<# } region.End(); //////// //////// Write Navigation properties ------------------------------------------------------------------------------------------- //////// region.Begin("Navigation Properties"); foreach (NavigationProperty navProperty in entity.NavigationProperties.Where(np => np.DeclaringType == entity)) { NavigationProperty inverse = ef.Inverse(navProperty); if (inverse != null && !IsReadWriteAccessibleProperty(inverse)) { inverse = null; }#><# if (navProperty.ToEndMember.RelationshipMultiplicity == RelationshipMultiplicity.Many) {#> <#=PropertyVirtualModifier(Accessibility.ForReadOnlyProperty(navProperty))#> ICollection<<#=code.Escape(navProperty.ToEndMember.GetEntityType())#>> <#=code.Escape(navProperty)#> { get { if (<#=code.FieldName(navProperty)#> == null) {<# if (inverse != null || ((AssociationType)navProperty.RelationshipType).IsForeignKey) {#> var newCollection = new FixupCollection<<#=code.Escape(navProperty.ToEndMember.GetEntityType())#>>(); newCollection.CollectionChanged += Fixup<#=navProperty.Name#>; <#=code.FieldName(navProperty)#> = newCollection;<# } else {#> <#=code.FieldName(navProperty)#> = new FixupCollection<<#=code.Escape(navProperty.ToEndMember.GetEntityType())#>>();<# }#> } return <#=code.FieldName(navProperty)#>; } set {<# if (inverse != null || ((AssociationType)navProperty.RelationshipType).IsForeignKey) {#> if (!ReferenceEquals(<#=code.FieldName(navProperty)#>, value)) { var previousValue = <#=code.FieldName(navProperty)#> as FixupCollection<<#=code.Escape(navProperty.ToEndMember.GetEntityType())#>>; if (previousValue != null) { previousValue.CollectionChanged -= Fixup<#=navProperty.Name#>; } <#=code.FieldName(navProperty)#> = value; var newValue = value as FixupCollection<<#=code.Escape(navProperty.ToEndMember.GetEntityType())#>>; if (newValue != null) { newValue.CollectionChanged += Fixup<#=navProperty.Name#>; } }<# } else {#> <#=code.FieldName(navProperty)#> = value;<# }#> } } private ICollection<<#=code.Escape(navProperty.ToEndMember.GetEntityType())#>> <#=code.FieldName(navProperty)#>;<# } else {#> <#=PropertyVirtualModifier(Accessibility.ForProperty(navProperty))#> <#=code.Escape(navProperty.ToEndMember.GetEntityType())#> <#=code.Escape(navProperty)#> {<# if (inverse != null || ((AssociationType)navProperty.RelationshipType).IsForeignKey) {#> <#=code.SpaceAfter(Accessibility.ForGetter(navProperty))#>get { return <#=code.FieldName(navProperty)#>; } <#=code.SpaceAfter(Accessibility.ForSetter(navProperty))#>set { if (!ReferenceEquals(<#=code.FieldName(navProperty)#>, value)) { var previousValue = <#=code.FieldName(navProperty)#>; <#=code.FieldName(navProperty)#> = value; Fixup<#=navProperty.Name#>(previousValue); } } } private <#=code.Escape(navProperty.ToEndMember.GetEntityType())#> <#=code.FieldName(navProperty)#>;<# } else {#> <#=code.SpaceAfter(Accessibility.ForGetter(navProperty))#>get; <#=code.SpaceAfter(Accessibility.ForSetter(navProperty))#>set; }<# } } } region.End(); region.Begin("Association Fixup"); if (entityHasNullableFKs) {#> private bool _settingFK = false;<# } foreach (NavigationProperty navProperty in entity.NavigationProperties.Where(np => np.DeclaringType == entity)) { NavigationProperty inverse = ef.Inverse(navProperty); if (inverse != null && !IsReadWriteAccessibleProperty(inverse)) { inverse = null; } if ( (inverse != null || ((AssociationType)navProperty.RelationshipType).IsForeignKey) && (navProperty.ToEndMember.RelationshipMultiplicity != RelationshipMultiplicity.Many) ) { var skipKeysArgument = (navProperty.GetDependentProperties().Where(p=>ef.IsNullable(p)).Any() && navProperty.GetDependentProperties().Count() > 1) ? ", bool skipKeys = false" : String.Empty;#> private void Fixup<#=navProperty.Name#>(<#=code.Escape(navProperty.ToEndMember.GetEntityType())#> previousValue<#= skipKeysArgument #>) {<# if (inverse != null) { if (inverse.ToEndMember.RelationshipMultiplicity == RelationshipMultiplicity.Many) {#> if (previousValue != null && previousValue.<#=code.Escape(inverse)#>.Contains(this)) { previousValue.<#=code.Escape(inverse)#>.Remove(this); }<# } else {#> if (previousValue != null && ReferenceEquals(previousValue.<#=code.Escape(inverse)#>, this)) { previousValue.<#=code.Escape(inverse)#> = null; }<# } if (inverse.ToEndMember.RelationshipMultiplicity == RelationshipMultiplicity.Many) {#> if (<#=code.Escape(navProperty)#> != null) { if (!<#=code.Escape(navProperty)#>.<#=code.Escape(inverse)#>.Contains(this)) { <#=code.Escape(navProperty)#>.<#=code.Escape(inverse)#>.Add(this); }<# foreach (var dependentProperty in navProperty.GetDependentProperties()) { EdmProperty principalProperty = ef.GetCorrespondingPrincipalProperty(navProperty, dependentProperty); if (((PrimitiveType)principalProperty.TypeUsage.EdmType).PrimitiveTypeKind == PrimitiveTypeKind.Binary) {#> if (!StructuralComparisons.StructuralEqualityComparer.Equals(<#=code.Escape(dependentProperty)#>, <#=code.Escape(navProperty)#>.<#=code.Escape(principalProperty)#>))<# } else {#> if (<#=code.Escape(dependentProperty)#> != <#=code.Escape(navProperty)#>.<#=code.Escape(principalProperty)#>)<# }#> { <#=code.Escape(dependentProperty)#> = <#=code.Escape(navProperty)#>.<#=code.Escape(principalProperty)#>; }<# }#> }<# if (navProperty.GetDependentProperties().Where(p=>ef.IsNullable(p)).Any()) { if (navProperty.GetDependentProperties().Count() > 1) {#> else if (!_settingFK && !skipKeys)<# } else {#> else if (!_settingFK)<# }#> {<# foreach (var dependentProperty in navProperty.GetDependentProperties().Where(p => ef.IsNullable(p))) {#> <#=code.Escape(dependentProperty)#> = null;<# }#> }<# } } else {#> if (<#=code.Escape(navProperty)#> != null) { <#=code.Escape(navProperty)#>.<#=code.Escape(inverse)#> = this;<# foreach (var dependentProperty in navProperty.GetDependentProperties()) { EdmProperty principalProperty = ef.GetCorrespondingPrincipalProperty(navProperty, dependentProperty); if (((PrimitiveType)principalProperty.TypeUsage.EdmType).PrimitiveTypeKind == PrimitiveTypeKind.Binary) {#> if (!StructuralComparisons.StructuralEqualityComparer.Equals(<#=code.Escape(dependentProperty)#>, <#=code.Escape(navProperty)#>.<#=code.Escape(principalProperty)#>))<# } else {#> if (<#=code.Escape(dependentProperty)#> != <#=code.Escape(navProperty)#>.<#=code.Escape(principalProperty)#>)<# }#> { <#=code.Escape(dependentProperty)#> = <#=code.Escape(navProperty)#>.<#=code.Escape(principalProperty)#>; }<# }#> }<# } } else { if (navProperty.GetDependentProperties().Any()) {#> if (<#=code.Escape(navProperty)#> != null) {<# foreach (var dependentProperty in navProperty.GetDependentProperties()) { EdmProperty principalProperty = ef.GetCorrespondingPrincipalProperty(navProperty, dependentProperty); if (((PrimitiveType)principalProperty.TypeUsage.EdmType).PrimitiveTypeKind == PrimitiveTypeKind.Binary) {#> if (!StructuralComparisons.StructuralEqualityComparer.Equals(<#=code.Escape(dependentProperty)#>, <#=code.Escape(navProperty)#>.<#=code.Escape(principalProperty)#>))<# } else {#> if (<#=code.Escape(dependentProperty)#> != <#=code.Escape(navProperty)#>.<#=code.Escape(principalProperty)#>)<# }#> { <#=code.Escape(dependentProperty)#> = <#=code.Escape(navProperty)#>.<#=code.Escape(principalProperty)#>; }<# }#> }<# if (navProperty.GetDependentProperties().Where(p => ef.IsNullable(p)).Any()) { if (navProperty.GetDependentProperties().Count() > 1) {#> else if (!_settingFK && !skipKeys)<# } else {#> else if (!_settingFK)<# }#> {<# foreach (var dependentProperty in navProperty.GetDependentProperties().Where(p => ef.IsNullable(p))) {#> <#=code.Escape(dependentProperty)#> = null;<# }#> }<# } } else if (((AssociationType)navProperty.RelationshipType).IsForeignKey) {#> if (<#=code.Escape(navProperty)#> != null) {<# foreach (var fromProperty in ef.GetPrincipalProperties(navProperty)) {#> <#=code.Escape(navProperty)#>.<#=code.Escape(ef.GetCorrespondingDependentProperty(navProperty, fromProperty))#> = <#=code.Escape(fromProperty)#>;<# }#> }<# } }#> }<# } } foreach (NavigationProperty navProperty in entity.NavigationProperties.Where(np => np.DeclaringType == entity)) { NavigationProperty inverse = ef.Inverse(navProperty); if (inverse != null && !IsReadWriteAccessibleProperty(inverse)) { inverse = null; } if ( (inverse != null || ((AssociationType)navProperty.RelationshipType).IsForeignKey) && (navProperty.ToEndMember.RelationshipMultiplicity == RelationshipMultiplicity.Many) ) {#> private void Fixup<#=navProperty.Name#>(object sender, NotifyCollectionChangedEventArgs e) { if (e.NewItems != null) { foreach (<#=code.Escape(navProperty.ToEndMember.GetEntityType())#> item in e.NewItems) {<# if (inverse != null) { if (inverse.ToEndMember.RelationshipMultiplicity != RelationshipMultiplicity.Many) {#> item.<#=code.Escape(inverse)#> = this;<# } else {#> if (!item.<#=code.Escape(inverse)#>.Contains(this)) { item.<#=code.Escape(inverse)#>.Add(this); }<# } } else if (((AssociationType)navProperty.RelationshipType).IsForeignKey) { foreach (var fromProperty in ef.GetPrincipalProperties(navProperty)) {#> item.<#=code.Escape(ef.GetCorrespondingDependentProperty(navProperty, fromProperty))#> = <#=code.Escape(fromProperty)#>;<# } }#> } } if (e.OldItems != null) { foreach (<#=code.Escape(navProperty.ToEndMember.GetEntityType())#> item in e.OldItems) {<# if (inverse != null) { if (inverse.ToEndMember.RelationshipMultiplicity != RelationshipMultiplicity.Many) {#> if (ReferenceEquals(item.<#=code.Escape(inverse)#>, this)) { item.<#=code.Escape(inverse)#> = null; }<# } else {#> if (item.<#=code.Escape(inverse)#>.Contains(this)) { item.<#=code.Escape(inverse)#>.Remove(this); }<# } } else if (((AssociationType)navProperty.RelationshipType).IsForeignKey) { foreach (var fromProperty in ef.GetPrincipalProperties(navProperty)) { var p = ef.GetCorrespondingDependentProperty(navProperty, fromProperty); if (ef.IsNullable(p.TypeUsage)) {#> item.<#=code.Escape(p)#> = null;<# } } };#> } } }<# } } region.End();#>}<# EndNamespace(namespaceName);}foreach (ComplexType complex in ItemCollection.GetItems<ComplexType>().OrderBy(e => e.Name)){ fileManager.StartNewFile(complex.Name + ".cs"); BeginNamespace(namespaceName, code);#><#=Accessibility.ForType(complex)#> partial class <#=code.Escape(complex)#>{<# region.Begin("Primitive Properties"); foreach(EdmProperty edmProperty in complex.Properties.Where(p => p.TypeUsage.EdmType is PrimitiveType && p.DeclaringType == complex)) { bool isDefaultValueDefinedInModel = (edmProperty.DefaultValue != null);#> <#=Accessibility.ForProperty(edmProperty)#> <#=code.Escape(edmProperty.TypeUsage)#> <#=code.Escape(edmProperty)#><# if (isDefaultValueDefinedInModel) {#> { <#=code.SpaceAfter(Accessibility.ForGetter(edmProperty))#>get { return <#=code.FieldName(edmProperty)#>; } <#=code.SpaceAfter(Accessibility.ForSetter(edmProperty))#>set { <#=code.FieldName(edmProperty)#> = value; } } private <#=code.Escape(edmProperty.TypeUsage)#> <#=code.FieldName(edmProperty)#><#=code.StringBefore(" = ", code.CreateLiteral(edmProperty.DefaultValue))#>;<# } else {#> { <#=code.SpaceAfter(Accessibility.ForGetter(edmProperty))#>get; <#=code.SpaceAfter(Accessibility.ForSetter(edmProperty))#>set; }<# } } region.End(); region.Begin("Complex Properties"); foreach(EdmProperty edmProperty in complex.Properties.Where(p => p.TypeUsage.EdmType is ComplexType && p.DeclaringType == complex)) {#> <#=Accessibility.ForProperty(edmProperty)#> <#=code.Escape(edmProperty.TypeUsage)#> <#=code.Escape(edmProperty)#> { <#=code.SpaceAfter(Accessibility.ForGetter(edmProperty))#>get { return <#=code.FieldName(edmProperty)#>; } <#=code.SpaceAfter(Accessibility.ForSetter(edmProperty))#>set { <#=code.FieldName(edmProperty)#> = value; } } private <#=code.Escape(edmProperty.TypeUsage)#> <#=code.FieldName(edmProperty)#> = new <#=code.Escape(edmProperty.TypeUsage)#>();<# } region.End();#>}<# EndNamespace(namespaceName);}if (!VerifyTypesAreCaseInsensitiveUnique(ItemCollection)){ return "";}fileManager.Process();#><#+void WriteHeader(EntityFrameworkTemplateFileManager fileManager, params string[] extraUsings){ fileManager.StartHeader();#>//------------------------------------------------------------------------------// <auto-generated>// This code was generated from a template.//// Changes to this file may cause incorrect behavior and will be lost if// the code is regenerated.// </auto-generated>//------------------------------------------------------------------------------using System;using System.Collections;using System.Collections.Generic;using System.Collections.ObjectModel;using System.Collections.Specialized;<#=String.Join(String.Empty, extraUsings.Select(u => "using " + u + ";" + Environment.NewLine).ToArray())#><#+ fileManager.EndBlock();}void BeginNamespace(string namespaceName, CodeGenerationTools code){ CodeRegion region = new CodeRegion(this); if (!String.IsNullOrEmpty(namespaceName)) {#>namespace <#=code.EscapeNamespace(namespaceName)#>{<#+ PushIndent(CodeRegion.GetIndent(1)); }}void EndNamespace(string namespaceName){ if (!String.IsNullOrEmpty(namespaceName)) { PopIndent();#>}<#+ }}bool IsReadWriteAccessibleProperty(EdmMember member){ string setter = Accessibility.ForWriteOnlyProperty(member); string getter = Accessibility.ForReadOnlyProperty(member); return getter != "private" && getter != "protected" && setter != "private" && setter != "protected";}string PropertyVirtualModifier(string accessibility){ return accessibility + (accessibility != "private" ? " virtual" : "");}void WriteCustomObservableCollection(){#>// An System.Collections.ObjectModel.ObservableCollection that raises// individual item removal notifications on clear and prevents adding duplicates.public class FixupCollection<T> : ObservableCollection<T>{ protected override void ClearItems() { new List<T>(this).ForEach(t => Remove(t)); } protected override void InsertItem(int index, T item) { if (!this.Contains(item)) { base.InsertItem(index, item); } }}<#+}bool VerifyTypesAreCaseInsensitiveUnique(EdmItemCollection itemCollection){ Dictionary<string, bool> alreadySeen = new Dictionary<string, bool>(StringComparer.OrdinalIgnoreCase); foreach(StructuralType type in itemCollection.GetItems<StructuralType>()) { if (!(type is EntityType || type is ComplexType)) { continue; } if (alreadySeen.ContainsKey(type.FullName)) { Error(String.Format(CultureInfo.CurrentCulture, "This template does not support types that differ only by case, the types {0} are not supported", type.FullName)); return false; } else { alreadySeen.Add(type.FullName, true); } } return true;}#>看起来很长？其实主要内容并不复杂。我们所要关心的的Entity生成代码都在一个遍历所有entity的foreach中，对于每个entity，它依次枚举Primitive Properties - entity本身定义的基本类型字段，Complex Properties - 用户定义的复杂类型字段，以及Navigation Properties - entity的关系字段。
首先找到生成每个类定义的代码：
<#=Accessibility.ForType(entity)#> <#=code.SpaceAfter(code.AbstractOption(entity))#>partial class <#=code.Escape(entity)#><#=code.StringBefore(" : ", code.Escape(entity.BaseType))#>在上面加一行：
[DataContract(Name = "<#=char.ToLowerInvariant(entity.Name[0]) + entity.Name.Substring(1) #>")]然后再找到生成Primitive Property的代码（其他的类似）：
<#=PropertyVirtualModifier(Accessibility.ForProperty(edmProperty))#> <#=code.Escape(edmProperty.TypeUsage)#> <#=code.Escape(edmProperty)#>在上面加一行：
[DataMember(Name = "<#=char.ToLowerInvariant(edmProperty.Name[0]) + edmProperty.Name.Substring(1) #>")]由于DataContract在System.Runtime.Serialization命名空间下，我们还需要添加命名空间。在接近Model.tt末尾的地方找到有一堆命名空间定义，在末尾加上：
using System.Runtime.Serialization;然后Save，这时代码会重新生成，我们再看一下这时的Microblog.cs:
//------------------------------------------------------------------------------// <auto-generated>// This code was generated from a template.//// Changes to this file may cause incorrect behavior and will be lost if// the code is regenerated.// </auto-generated>//------------------------------------------------------------------------------using System;using System.Collections;using System.Collections.Generic;using System.Collections.ObjectModel;using System.Collections.Specialized;using System.Runtime.Serialization;namespace WcfRestServiceDemo.Data{ [DataContract(Name = "microblog")] public partial class Microblog { #region Primitive Properties [DataMember(Name = "id")] public virtual int Id { get; set; } [DataMember(Name = "content")] public virtual string Content { get; set; } [DataMember(Name = "publishTime")] public virtual System.DateTime PublishTime { get; set; } #endregion }}这时如果测试一下服务，就可以看到不论是XML还是JSON的返回结果中的字段都已经变成小写字母开头了。
需要注意的是，不仅是返回，这时客户端发送请求时，对应字段也必须同样改成小写字母开头。
处理Null值属性
为了引入这个问题，我们将服务稍稍变得复杂一些。假设现在并且每条微博可以关联一张图片，用户只要在写微博同时，输入图片地址即可。那么修改Microblog模型，添加Picture属性，包含一个图片的URL。由于图片是可选的，所以还要将的Nullable设为true。
如下：
由于修改了EntityModel，需要在两个.tt模板文件上右键选择Run Custom Tools来生成新的POCO entity.
然后我们看一下服务的返回：
<ArrayOfmicroblog xmlns="http://schemas.datacontract.org/2004/07/WcfRestServiceDemo.Data" xmlns:i="http://www.w3.org/2001/XMLSchema-instance"> <microblog> <content>Microblog with no picture.</content> <id>1</id> <picture i:nil="true"/> <publishTime>2011-04-19T22:00:00</publishTime> </microblog> <microblog> <content>Microblog with picture</content> <id>2</id> <picture>http://somepicture/somepicture</picture> <publishTime>2011-04-19T22:00:00</publishTime> </microblog></ArrayOfmicroblog>这里有两条microblog，一条有picture，一条没有。但是没有picture的那个也把picture字段给返回了，只是用i:nil=”true”来标识这是个null值。显然这不是理想方式，想象一下一个entity可能会有很多可空的属性，尤其是当一个entity与许多其他entity产生关联，引入了许多navigation properties时，传输这些空属性将严重影响可读性（虽然大多数情况下应该不是人来读）并对性能造成影响（传输、序列化和反序列化）。（当然这不是绝对的，nil值有其应用场景，请根据实际情况决定）
幸好DataMember attribute还有一个EmitDefaultValue属性，可以指定是否要序列化默认值。用和刚才类似的方法，修改T4模板，修改Property定义上方的[DataMember]:
[DataMember(Name = "<#=char.ToLowerInvariant(edmProperty.Name[0]) + edmProperty.Name.Substring(1) #>"<#if(edmProperty.Nullable){#>, EmitDefaultValue = false<#}#>)]首先判断了property是否可设为null，若可以才省略空值。否则对于一个int属性，值为0时它就不会被传输了，这一般是不太合适的。（确切的讲，这里的Nullable和数据类型没有关系，指的是在数据模型中的nullable，也就是是否为可空字段。)再次访问服务：
<ArrayOfmicroblog xmlns="http://schemas.datacontract.org/2004/07/WcfRestServiceDemo.Data" xmlns:i="http://www.w3.org/2001/XMLSchema-instance"> <microblog> <content>Microblog with no picture.</content> <id>1</id> <publishTime>2011-04-19T22:00:00</publishTime> </microblog> <microblog> <content>Microblog with picture</content> <id>2</id> <picture>http://somepicture/somepicture</picture> <publishTime>2011-04-19T22:00:00</publishTime> </microblog></ArrayOfmicroblog>可以看到没有图片的那个microblog的picture属性已经被省略了。
JSON中的DateTime
在第二章末尾我们提到过DateTime属性在JSON表示下的奇怪格式。严格来说，这不算什么问题，因为既然微软选择了这种格式，那么全世界的人都在碰到这个问题，相应的客户端解决方案也有很多。比如：
- http://archive.cnblogs.com/a/1444633/
- http://stackoverflow.com/questions/206384/how-to-format-json-date
如果一定要从服务端解决这个问题的话，最根本的方法是改用自定义的序列化器。而比较简单的方法是为entity写一个partial类，然后提供一个long格式的对应属性：
using System;using System.Runtime.Serialization;namespace WcfRestServiceDemo.Data{ partial class Microblog { private static readonly DateTime _baseTime = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc).ToLocalTime(); [DataMember(Name = "publishTimeSec")] public long PublishTimeSeconds { get { return (long)(PublishTime - _baseTime).TotalMilliseconds; } set { PublishTime = _baseTime.AddMilliseconds(value); } } }}这时服务的返回就是：
[ { "content":"Microblog with no picture.", "id":1, "publishTime":"\/Date(1303221600000+0800)\/", "publishTimeSec":1303221600000 }, { "content":"Microblog with picture", "id":2, "picture":"http:\/\/somepicture\/somepicture", "publishTime":"\/Date(1303221600000+0800)\/", "publishTimeSec":1303221600000 }]当然更绝的做法是把这个替代属性的生成也交给T4模板来做。具体做法请参考我整理好后上传的代码。
小结
本文介绍了:
- 如何修改T4模板控制模型代码的生成，包括修改Type名称、属性名称的起始字母大小写和是否要序列化默认值的选项
- 如何用替代属性解决JSON中DateTime格式的问题。
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