实体框架代码优先使用本地数据库，但部署到 Azure 时出错

Question

我开发了一个使用 Asp.Net Web API 的项目，遵循 Entity Framework code-first 方法。

我已经在 Visual Studio 2013 中使用本地数据库在本地机器上对其进行了测试，它可以正常工作。

当我替换连接字符串并将数据库部署到 Azure 时，问题就出现了。我可以执行一些查询，但不能执行其他查询。

例如，如果我在浏览器中输入 http://my-site/api/users/1 我会得到预期的结果。但是查询http://my-site/api/users/ 向我返回了与Json 序列化相关的错误：

{ "$id" : "1",
  "ExceptionMessage" : "The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json; charset=utf-8'.",
  "ExceptionType" : "System.InvalidOperationException",
  "InnerException" : { "$id" : "2",
      "ExceptionMessage" : "Error getting value from 'Devices' on 'System.Data.Entity.DynamicProxies.User_50420314CCDC05AAF3288A574C1CBB8436C09BAEF7539C2795445FCBA161AC99'.",
      "ExceptionType" : "Newtonsoft.Json.JsonSerializationException",
      "InnerException" : { "$id" : "3",
          "ExceptionMessage" : "An error occurred while executing the command definition. See the inner exception for details.",
          "ExceptionType" : "System.Data.Entity.Core.EntityCommandExecutionException",
          "InnerException" : { "$id" : "4",
              "ExceptionMessage" : "There is already an open DataReader associated with this Command which must be closed first.",
              "ExceptionType" : "System.InvalidOperationException",
              "Message" : "An error has occurred.",
              "StackTrace" : "   at System.Data.SqlClient.SqlInternalConnectionTds.ValidateConnectionForExecute(SqlCommand command)\r\n   at System.Data.SqlClient.SqlConnection.ValidateConnectionForExecute(String method, SqlCommand command)\r\n   at System.Data.SqlClient.SqlCommand.ValidateCommand(String method, Boolean async)\r\n   at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, TaskCompletionSource`1 completion, Int32 timeout, Task& task, Boolean asyncWrite)\r\n   at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method)\r\n   at System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior, String method)\r\n   at System.Data.SqlClient.SqlCommand.ExecuteDbDataReader(CommandBehavior behavior)\r\n   at System.Data.Common.DbCommand.ExecuteReader(CommandBehavior behavior)\r\n   at System.Data.Entity.Infrastructure.Interception.DbCommandDispatcher.<>c__DisplayClassb.<Reader>b__8()\r\n   at System.Data.Entity.Infrastructure.Interception.InternalDispatcher`1.Dispatch[TInterceptionContext,TResult](Func`1 operation, TInterceptionContext interceptionContext, Action`1 executing, Action`1 executed)\r\n   at System.Data.Entity.Infrastructure.Interception.DbCommandDispatcher.Reader(DbCommand command, DbCommandInterceptionContext interceptionContext)\r\n   at System.Data.Entity.Internal.InterceptableDbCommand.ExecuteDbDataReader(CommandBehavior behavior)\r\n   at System.Data.Common.DbCommand.ExecuteReader(CommandBehavior behavior)\r\n   at System.Data.Entity.Core.EntityClient.Internal.EntityCommandDefinition.ExecuteStoreCommands(EntityCommand entityCommand, CommandBehavior behavior)"
            },
          "Message" : "An error has occurred.",
          "StackTrace" : "   at System.Data.Entity.Core.EntityClient.Internal.EntityCommandDefinition.ExecuteStoreCommands(EntityCommand entityCommand, CommandBehavior behavior)\r\n   at System.Data.Entity.Core.Objects.Internal.ObjectQueryExecutionPlan.Execute[TResultType](ObjectContext context, ObjectParameterCollection parameterValues)\r\n   at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClassb.<GetResults>b__a()\r\n   at System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func`1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess)\r\n   at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClassb.<GetResults>b__9()\r\n   at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute[TResult](Func`1 operation)\r\n   at System.Data.Entity.Core.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption)\r\n   at System.Data.Entity.Core.Objects.ObjectQuery`1.Execute(MergeOption mergeOption)\r\n   at System.Data.Entity.Core.Objects.DataClasses.EntityCollection`1.Load(List`1 collection, MergeOption mergeOption)\r\n   at System.Data.Entity.Core.Objects.DataClasses.EntityCollection`1.Load(MergeOption mergeOption)\r\n   at System.Data.Entity.Core.Objects.DataClasses.RelatedEnd.Load()\r\n   at System.Data.Entity.Core.Objects.DataClasses.RelatedEnd.DeferredLoad()\r\n   at System.Data.Entity.Core.Objects.Internal.LazyLoadBehavior.LoadProperty[TItem](TItem propertyValue, String relationshipName, String targetRoleName, Boolean mustBeNull, Object wrapperObject)\r\n   at System.Data.Entity.Core.Objects.Internal.LazyLoadBehavior.<>c__DisplayClass7`2.<GetInterceptorDelegate>b__1(TProxy proxy, TItem item)\r\n   at System.Data.Entity.DynamicProxies.User_50420314CCDC05AAF3288A574C1CBB8436C09BAEF7539C2795445FCBA161AC99.get_Devices()\r\n   at GetDevices(Object )\r\n   at Newtonsoft.Json.Serialization.DynamicValueProvider.GetValue(Object target)"
        },
      "Message" : "An error has occurred.",
      "StackTrace" : "   at Newtonsoft.Json.Serialization.DynamicValueProvider.GetValue(Object target)\r\n   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.CalculatePropertyValues(JsonWriter writer, Object value, JsonContainerContract contract, JsonProperty member, JsonProperty property, JsonContract& memberContract, Object& memberValue)\r\n   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IEnumerable values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter, Object value, Type objectType)\r\n   at Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter, Object value, Type objectType)\r\n   at Newtonsoft.Json.JsonSerializer.Serialize(JsonWriter jsonWriter, Object value)\r\n   at System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, Encoding effectiveEncoding)\r\n   at System.Net.Http.Formatting.JsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, Encoding effectiveEncoding)\r\n   at System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, HttpContent content)\r\n   at System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStreamAsync(Type type, Object value, Stream writeStream, HttpContent content, TransportContext transportContext, CancellationToken cancellationToken)\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.GetResult()\r\n   at System.Web.Http.WebHost.HttpControllerHandler.<WriteBufferedResponseContentAsync>d__19.MoveNext()"
    },
  "Message" : "An error has occurred.",
  "StackTrace" : null
}

这个问题真的让我很恼火，因为正如我所提到的，使用本地数据库可以正常工作。本地生成的数据库和 Azure 中生成的数据库似乎相同。所以，我猜不出问题出在哪里。

Answer 1

答案就是错误消息告诉您的内容。它无法将实体框架代理序列化为 JSON。您应该映射到 POCO 类并返回它们：

//poco
    public class PersonPoco
    {
       public string FirstName {get;set;}
       public string LastName {get;set;}
    }

//控制器

public IEnumerable<PersonPoco> Get()
{
    var person = _personRepository.FindAll();

    person.Select(x=> new PersonPoco() {
     FirstName = x.f_name,
     LastName = x.l_name
    }).ToList();
}

你可以使用 AutoMapper 来做这个转换，你可以创建扩展方法来做这个转换。无论如何，这只是一个样本。

Answer 2

将 .ToArray() 添加到我从 GetAll() 方法返回的结果中解决了问题：

    public IEnumerable<TEntity> GetAll()
    {
        return _dbContext.Set<TEntity>().ToArray();
    }

但是，我仍然想知道为什么它使用本地数据库而不是部署到 Azure 的数据库。

添加MultipleActiveResultSets=True 也解决了我的问题。但由于我真的不知道启用该功能需要什么，所以我选择了第一个选项。