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 file
WriteHeader(fileManager);
BeginNamespace(namespaceName, code);
WriteCustomObservableCollection();
EndNamespace(namespaceName);
// Emit Entity Types
foreach (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。
我的WCF4 REST Service及Entity Framework with POCO之旅系列
- 我的WCF4 REST Service及Entity Framework with POCO之旅（一）——创建一个基本的RESTful Service
- 我的WCF4 REST Service及Entity Framework with POCO之旅（二）——选择请求/返回格式
- 我的WCF4 REST Service及Entity Framework with POCO之旅（三）——用Entity Framework和POCO Template实现数据模型及存储
- 我的WCF4 REST Service及Entity Framework with POCO之旅（四）——定制Entity
- 我的WCF4 REST Service及Entity Framework with POCO之旅（五）——身份验证