Web API和EF导致InvalidOperationException [英] Web API and EF cause InvalidOperationException

问题描述

我的解决方案中有3个项目:DataModel(EF)，DAL，可与DataModel和MVC Web API中的实体一起使用.

I have 3 projects in my solution: DataModel (EF), DAL which works with Entities from DataModel and MVC Web API.

只有2个非常简单的实体:人"，地址"中每个都有3个简单字段，人"具有地址"字段(因此这2个实体是链接的)

There are only 2 very simple entities: Person, Address with 3 simple fields in each of them and Person has the Address field (so these 2 entities are linked)

在我的DAL中，我有一个方法可以向我返回所有人员的列表，内容非常简单:return context.Person.ToList();

In my DAL I have a method that returns me the list of all the Persons, the content is very simple: return context.Person.ToList();

现在在我的Web API中，我只是调用GetPersons()方法并尝试返回它. 在这里，我收到一条奇怪的错误消息:

Now In my Web API I'm simply calling for the GetPersons() method and trying to return it. And here I get a strange error message:

发生错误."，"ExceptionMessage":'ObjectContent`1' 类型未能序列化内容类型的响应正文 'application/json; charset = utf-8'.，" ExceptionType:" System.InvalidOperationException，" StackTrace:null，" InnerException:{" $ id:" 2，" Message:" An 错误发生了.，...

"An error has occurred.","ExceptionMessage":"The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json; charset=utf-8'.","ExceptionType":"System.InvalidOperationException","StackTrace":null,"InnerException":{"$id":"2","Message":"An error has occurred.",...

当我调试时，我可以看到我确实有GetPersons方法中的数据. 我还用谷歌搜索并找到了唯一的解决方案:我应该在我的启动配置中添加以下几行:

When I debug I can see that I do have the data from my GetPersons method. I also googled and found the only solution: I should have added the following lines into my start config:

var json = config.Formatters.JsonFormatter;
json.SerializerSettings.PreserveReferencesHandling = Newtonsoft.Json.PreserveReferencesHandling.Objects;
config.Formatters.Remove(config.Formatters.XmlFormatter);

但这没有帮助.

我还尝试不使用数据库手动填充列表:在这种情况下，它可以正常工作.

I also tried to populate the list manually without using the database: and in this case it works.

我有一个很强烈的印象，那就是它与EF有关，但我不知道那到底是什么.

I have a strong impression that it has something to do with EF but I don't know exactly what's that.

推荐答案

• 分步指南...

步骤1:转到您的实体项目，然后找到从DbContext类继承的类的名称.

Step 1: Go to your Entity Project and then find the name of the class which inherits from DbContext class.

例如:如果类名称为MyProjectEntities，如下所示:

For Example: If the class name is MyProjectEntities as follows:

public partial class MyProjectEntities : DbContext
{
   //Auto Generated statements if EF is used.
}

步骤2:转到您的WebApi项目，找到继承自ApiController的控制器，然后在该控制器中为MyProjectEntities类创建实例.

Step 2: Go to your WebApi Project find the controller which inherits from ApiController and then create the instance for the MyProjectEntities class within that controller.

例如:如果Api控制器的名称为PersonController，则为MyProjectEntities创建实例，如下所示:

For Example: If the Api Controller name is PersonController then create the instance for MyProjectEntities as follows:

public class PersonController : ApiController
{
   MyProjectEntities DB = new MyProjectEntities();
}

步骤3:，为PersonController类创建构造函数，并将ProxyCreationEnabled属性设置为false，如下所示:

Step 3: Create constructor for the PersonController class and set false to the ProxyCreationEnabled Property as follows:

public PersonController()
{
   DB.Configuration.ProxyCreationEnabled = false;
}

Web api控制器中的最终代码类似于以下内容:

The final code within the web api controller looks similar to this:

public class PersonController : ApiController
{
   MyProjectEntities DB = new MyProjectEntities();
   public PersonController()
   {
      DB.Configuration.ProxyCreationEnabled = false;
   }
...
...

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