在契约版本管理的前二章，我们主要介绍了数据契约对版本的影响，本章我们介绍一下服务契约的变化对版本的影响。服务契约的接口支持继承功能，我们可以定义一个契约层级，但是ServiceContract特性是不能继承的，因此，接口层级中的每组接口都必须显示的标记ServiceContract特性。
下面我们通过一个DEMO来演示服务契约的继承：
1、新建WCF Service Library程序，修改解决方案名称为ContractVersion，修改项目名称为InheritanceContract，删除自动添加的文件。
2、新建接口IInheritanceServiceA，代码如下：
[ServiceContract(Name = "InheritanceServiceContract", Namespace = "http://schemas.xinhaijulan.com/demos/InheritanceServiceContract")]
interface IInheritanceServiceA
{
[OperationContract]
string Operation1();
[OperationContract]
string Operation2();
}
3、新建接口IInheritanceServiceA2，并继承接口IInheritanceServiceA，代码如下：
[ServiceContract(Name = "InheritanceServiceContract", Namespace = "http://schemas.xinhaijulan.com/demos/InheritanceServiceContract")]
interface IInheritanceServiceA2 : IInheritanceServiceA
{
[OperationContract]
string Operation3();
}
注意，每个接口都必须单独实现ServiceContract标记。
4、新建InheritanceService类，继承并实现接口IInheritanceServiceA，代码如下：
class InheritanceService : IInheritanceServiceA
{
public string Operation1()
{
return "IInheritanceServiceA.Operation1() invoked.";
}
public string Operation2()
{
return "IInheritanceServiceA.Operation2() invoked.";
}
}
5、修改App.config中的服务名称 、端点契约、服务地址，然后编译，代码如下：
代码
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<system.web>
<compilation debug="true" />
</system.web>
<!-- When deploying the service library project, the content of the config file must be added to the host's
app.config file. System.Configuration does not support config files for libraries. -->
<system.serviceModel>
<services>
<service name="InheritanceContract.InheritanceService">
<host>
<baseAddresses>
<add baseAddress = "http://localhost:8732/Design_Time_Addresses/InheritanceContract/InheritanceService/" />
</baseAddresses>
</host>
<!-- Service Endpoints -->
<!-- Unless fully qualified, address is relative to base address supplied above -->
<endpoint address ="" binding="wsHttpBinding" contract="InheritanceContract.IInheritanceServiceA">
<!--
Upon deployment, the following identity element should be removed or replaced to reflect the
identity under which the deployed service runs. If removed, WCF will infer an appropriate identity
automatically.
-->
<identity>
<dns value="localhost"/>
</identity>
</endpoint>
<!-- Metadata Endpoints -->
<!-- The Metadata Exchange endpoint is used by the service to describe itself to clients. -->
<!-- This endpoint does not use a secure binding and should be secured or removed before deployment -->
<endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange"/>
</service>
</services>
<behaviors>
<serviceBehaviors>
<behavior>
<!-- To avoid disclosing metadata information,
set the value below to false and remove the metadata endpoint above before deployment -->
<serviceMetadata httpGetEnabled="True"/>
<!-- To receive exception details in faults for debugging purposes,
set the value below to true. Set to false before deployment
to avoid disclosing exception information -->
<serviceDebug includeExceptionDetailInFaults="False" />
</behavior>
</serviceBehaviors>
</behaviors>
</system.serviceModel>
</configuration>
6、创建客户端控制台程序InheritanceClientA，添加Service Reference，修改名称空间为InheritanceContract，代码如下：
static void Main(string[] args)
{
using (InheritanceContract.InheritanceServiceContractClient client = new InheritanceContract.InheritanceServiceContractClient())
{
Console.WriteLine(client.Operation1());
Console.WriteLine(client.Operation2());
}
Console.ReadLine();
}
7、设置InheritanceClientA为启动项目，运行项目，将在控制台看到如下输出：
IInheritanceServiceA.Operation1() invoked.
IInheritanceServiceA.Operation2() invoked.
8、修改InheritanceService类，使之继承并实现IInheritanceServiceA2接口，【此时必须修改app.config文件中的端点的Contract的指向为新的接口：InheritanceContract.IInheritanceServiceA2】然后重新编译，代码如下：
<endpoint address ="" binding="wsHttpBinding" contract="InheritanceContract.IInheritanceServiceA2">
class InheritanceService : IInheritanceServiceA2
{
public string Operation1()
{
return "IInheritanceServiceA.Operation1() invoked.";
}
public string Operation2()
{
return "IInheritanceServiceA.Operation2() invoked.";
}
public string Operation3()
{
return "IInheritanceServiceA2.Operation3() invoked.";
}
}
9、创建客户端控制台程序InheritanceClientA2，添加Service Reference，修改名称空间为InheritanceContract，代码如下：
static void Main(string[] args)
{
using (InheritanceContract.InheritanceServiceContractClient client = new InheritanceContract.InheritanceServiceContractClient())
{
Console.WriteLine(client.Operation1());
Console.WriteLine(client.Operation2());
Console.WriteLine(client.Operation3());
}
Console.ReadLine();
}
10、设置InheritanceClientA2为启动项目，运行项目，将在控制台看到如下输出：
IInheritanceServiceA.Operation1() invoked.
IInheritanceServiceA.Operation2() invoked.
IInheritanceServiceA2.Operation3() invoked.
11、此时再次设置 InheritanceClientA为启动项目，运行项目，将在控制台看到如下输出：
IInheritanceServiceA.Operation1() invoked.
IInheritanceServiceA.Operation2() invoked.
从以上DEMO可以看出服务契约的继承不会对原来的客户端产生影响，然而这种不严格的版本管理是否应该采纳，还是应该根据具体的情况来进行权衡。
至此，WCF契约版本管理—服务契约的继承介绍完毕。
作者：心海巨澜
出处：http://xinhaijulan.cnblogs.com
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