Adding Using statement causes failure to serialize error

Question

User438705957 posted

I am using VS 2017.
I have a Web API 2 controller using EF. I  and am slowly introducing repository methods to access the db.
I initialize a new database context whenever the controller is invoked.

private CACS_GNS_DataContext db = new CACS_GNS_DataContext();

 Whenever I wrap the call to the async repository method in a using statement that disposes of the database context (db), it falls over with the message:
"The type failed to serialize the response body for the content type 'application/json'.
It makes it to the return statement, so the error takes place somewhere in the pipeline after the task is returned to the client.

If I don't wrap the call to the repository in a using statement, it works perfectly.
I am not sure why the using statement is interfering with the serialization process.

public async Task<IHttpActionResult> GetAuditsAsync(int skip, int take)
{
using (db)
{
	IAuditRepository auditRepository = new AuditRepository(db); 
	var returnTask = await auditRepository.GetListAsync(skip, take, defaultMngrPosition, refClass); 
	if (returnTask.Count() == 0)
		{
			return Ok(new { CustomErrorMessage = "No Audits were found that belonged to your designated Manager's position" });
		} 
	int allRecordCount = refClass.totalRecords;   
	HttpContext.Current.Response.Headers.Add("X-Paging-TotalRecordCount", allRecordCount.ToString());
	return Ok(returnTask);
}
}

Answer 1

User1120430333 posted

To me, the definition of returntask would be out of using scope along with everything else that has nothing to do with db context and the using statment.

using (db)
{
   IAuditRepository auditRepository = new AuditRepository(db); 
   returnTask = await auditRepository.GetListAsync(skip, take, defaultMngrPosition, refClass);
}

Answer 2

User438705957 posted

Thanks for your answer DA294.

If I place the using statement in the repository method ( auditRepository.GetListAsync(..)), and remove it from the controller method, I get the same result.

So I am not sure now how to deploy using and dispose of the context properly.

Answer 3

User1120430333 posted

Can you show what yo have done?

Answer 4

User438705957 posted

The controller method code is as shown in the first part of the answer.

The repository method code is this:

	public class AuditRepository : IAuditRepository, IDisposable
	{       
		private CACS_GNS_DataContext context;

		public AuditRepository(CACS_GNS_DataContext context)
		{
			this.context = context;
		}

		public async Task<List<Audit>> GetListAsync(int skip, int take, int defaultMngrPosition, refClass refClass)
		{
			// Returns all Audits for the default position with skip,take settings
			// refClass is passed to get around the limitation of not being able to have out parameters or parameters passed by reference in an asynch method
			
			try
			{				
				int qryTake = take == 0 ? 200000 : take;

				// Changed from IQueryable so it could be awaited
				var audits = await context.Audits
					.Where(a => a.Position_Id == defaultMngrPosition && a.Active == true && a.Finalised == false)
					.OrderBy(l => l.Audit_Due_Date).ThenBy(i => i.Location.Location_Name).Skip(skip).Take(qryTake).ToListAsync();

				var varTotalRecords = await context.Audits.Where(a => a.Position_Id == defaultMngrPosition && a.Active == true && a.Finalised == false).ToListAsync();
				refClass.totalRecords = varTotalRecords.Count();

				return audits;
			}
			catch (Exception ex)
			{               
				string exceptionMessage = ex.InnerException == null ? "Exception Message: " + ex.Message : "Exception Message: " + ex.Message + "Inner Exception Message: " + ex.InnerException.Message;
				string currentMethod = System.Reflection.MethodBase.GetCurrentMethod().Name.ToString();
				WriteTransactions.WriteTran("Error occurred in Repository Method: " + currentMethod, true, exceptionMessage);
				throw ex;   
			}
		}

        private bool disposed = false;

        protected virtual void Dispose(bool disposing)
        {
            if (!this.disposed)
            {
                if (disposing)
                {
                    context.Dispose();
                }
            }
            this.disposed = true;
        }

        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }
    }

Answer 5

User1120430333 posted

Now, it  could be that audits, a collection , is an attached collection to the DBcontect as you do the return audits that could be causing you problems.

In my example, the collection being sent back is a detached collection from the DB context through the WebAPi from the DAL using the DAO pattern 

var dtos = new List<DtoProject>()

The query dumps the results into dtos.

var audits = new List<audit>()  // or however you have to make the collection a detached collection.

audits - contect.audits.ToList()  // whatever you have to do and make it work with the detached collection .

try
			{				
				int qryTake = take == 0 ? 200000 : take;

				// Changed from IQueryable so it could be awaited
				var audits = await context.Audits
					.Where(a => a.Position_Id == defaultMngrPosition && a.Active == true && a.Finalised == false)
					.OrderBy(l => l.Audit_Due_Date).ThenBy(i => i.Location.Location_Name).Skip(skip).Take(qryTake).ToListAsync();

				var varTotalRecords = await context.Audits.Where(a => a.Position_Id == defaultMngrPosition && a.Active == true && a.Finalised == false).ToListAsync();
				refClass.totalRecords = varTotalRecords.Count();

				return audits;

public List<DtoProject> GetProjectsByUserId(string userid)
        {
            var dtos = new List<DtoProject>();

            using (var context = new ProjectManagementContext(_options))
            {
                
                dtos = (from a in context.Projects.Where(a => a.UserId.Contains(userid))
                    select new DtoProject
                    {
                        ProjectId = a.ProjectId,
                        ClientName = a.ClientName,
                        ProjectName = a.ProjectName,
                        Technology = a.Technology,
                        ProjectType = a.ProjectType,
                        UserId = a.UserId,
                        StartDate = a.StartDate,
                        EndDate = a.EndDate,
                        Cost = a.Cost
                    }).ToList();
            }

            return dtos;
        }

I see you have a try/catch there doing some logging. You don't have to have any try/catches not in the Repository or the controller too by doing global exception handling. The code you see that I have presented and the controller to have no try/catches anywhere.

What I did is at  the bottom of the link, and I just made the adjustment for non Core WebAPI that happens to be in VB..NET it works like a charm.

https://stackify.com/csharp-catch-all-exceptions/

Clint-side ASP.NET MVC code  knows the response is not 200  ok,  and it too does its global exception handling.

Imports System.Net
Imports System.Net.Http
Imports System.Web.Http.Filters
Imports log4net

Public Class CustomExceptionFilter
    Inherits ExceptionFilterAttribute

    private ReadOnly _logger As ILog

    public sub New()
        _logger = LogManager.GetLogger(GetType(CustomExceptionFilter))
    End sub

    Public Overrides Sub OnException(actionExecutedContext As HttpActionExecutedContext)
        MyBase.OnException(actionExecutedContext)

        Dim exceptionMessage as String = String.Empty

        If IsNothing(actionExecutedContext.Exception.InnerException ) Then
            exceptionMessage = actionExecutedContext.Exception.Message _
                               & " " & actionExecutedContext.Exception.StackTrace
        Else 
            exceptionMessage =  actionExecutedContext.Exception.Message _
                                & " " & actionExecutedContext.Exception.InnerException.Message _
                                & " " & actionExecutedContext.Exception.StackTrace
        End If

        _logger.Error(exceptionMessage)

        dim response =  New HttpResponseMessage(HttpStatusCode.InternalServerError)With {.Content = New StringContent(“An unhandled exception was thrown by service.”),
                .ReasonPhrase = "Internal Server Error.Please Contact your Administrator."}

        actionExecutedContext.Response = response

    End Sub
End Class

Imports System.Web.Http
Imports DAL
Imports Entities

Namespace Controllers

    <CustomExceptionFilter>
    Public Class ProjectController
        Inherits ApiController

        Private ReadOnly _daoproject As IDaoProject

        public sub New (daoproject As IDaoProject)
            _daoproject = daoproject
        End sub

        <HttpGet>
        <ActionName("GetProjectById")>
        public Function GetProjectById(ByVal id As Int32) As DtoProject
            return _daoproject.GetProjectById(id)
        End Function


        <HttpGet>
        <ActionName("GetProjectsByUserId")>
        public Function GetProjectsByUserId(ByVal userid As String) As List(Of DtoProject)
            return _daoproject.GetProjectsByUserId(userid)
        End Function

        <HttpPost>
        <ActionName("CreateProject")>
        public sub CreateProject(ByVal dto As DtoProject)
            Call _daoproject.CreateProject(dto)
        End sub
        
        <HttpPost>
        <ActionName("UpdateProject")>
        public sub UpdateProject(ByVal dto As DtoProject)
            Call _daoproject.UpdateProject(dto)
        End sub

        <HttpPost>
        <ActionName("DeleteProject")>
        public sub  DeleteProject(ByVal dto As DtoId)
            Call _daoproject.DeleteProject(dto.Id)
        End sub
        
    End Class
End Namespace

 

Answer 6

User438705957 posted

Thanks DA294, that is above and beyond and by far the most extensive answer I have had in any forum.<br>
I am going to study you’re code and create a solution of my own. I cleary have a lot to learn about the Repository pattern.<br>
Yes, I do use a custom exception filter in my other controller methods, with no try..catch. I haven’t got around to adding here yet.

Answer 7

User1120430333 posted

In using the repository pattern, you should understand it, becuase the repositroy is a domain object, a business object in Domain Driven Design,  that uses a mapping layer for CRUD operations, which originated in DDD.  

https://martinfowler.com/eaaCatalog/repository.html

<copied>

A Repository mediates between the domain and data mapping layers, acting like an in-memory domain object collection. Client objects construct query specifications declaratively and submit them to Repository for satisfaction.

<end>

https://programmingwithmosh.com/entity-framework/common-mistakes-with-the-repository-pattern/

Just in looking at the repository object that you have presented, it is void of any business logic or anemic in using business logic. It's just a glorified DAO.

https://blog.sapiensworks.com/post/2012/11/01/Repository-vs-DAO.aspx

<copied>

A repository sits at a higher level. It deals with data too and hides queries and all that but, a repository deals with** business/domain objects**. That's the difference. A repository will use a DAO to get the data from the storage and uses that data to restore a business object. Or it will take a business object and extract the data that will be persisted. If you have an anemic domain, the repository will be just a DAO. Also when dealing with querying stuff, most of the time a specialized query repository is just a DAO sending DTOs to a higher layer.

<end>

In the code I have presented, the DAO is sitting behind the WebAPI. The DAO is in the classlib project called the DAL (Data Access Layer), and  the WebAPI has reference to it. I am also using the DTO pattern and all projects, including client-side projects) have refernce to the DTO(s) that are kept in a classlib project called Entities. 

https://en.wikipedia.org/wiki/Data_access_object

https://www.tutorialspoint.com/design_pattern/data_access_object_pattern.htm

https://www.codeproject.com/Articles/1050468/Data-Transfer-Object-Design-Pattern-in-Csharp

Example...

mports Entities

Public Interface IDaoProject
    Function GetProjectById(ByVal id As Int32) As DtoProject
    Function GetProjectsByUserId(ByVal userid As String) As List(Of DtoProject)
    Sub CreateProject(ByVal dto As DtoProject)
    Sub UpdateProject(ByVal dto As DtoProject)
    Sub DeleteProject(ByVal id As Int32)
End Interface

==================================================


Imports System.Data.Entity
Imports Entities

Public Class DaoProject
    Implements IDaoProject

    Private ReadOnly context As ProjectManagementEntities

    public sub New (dbcontext As ProjectManagementEntities)
        context = dbcontext
    End sub

    Public Function GetProjectById(ByVal id As Int32) As DtoProject Implements IDaoProject.GetProjectById

        Dim dto = New DtoProject()
   
        Dim project = (context.Projects.Where(Function(a) a.ProjectId = id)).SingleOrDefault()

        If IsNothing(project) Then
            Return dto
        End If

        dto.ProjectId = project.ProjectId
        dto.ClientName = project.ClientName
        dto.ProjectName = project.ProjectName
        dto.Technology = project.Technology
        dto.ProjectType = project.ProjectType
        dto.UserId = project.UserId
        dto.StartDate = project.StartDate
        dto.EndDate = project.EndDate
        dto.Cost = project.Cost

        Return dto

    End Function

    Public Function GetProjectsByUserId(ByVal userid As String) As List(Of DtoProject) Implements IDaoProject.GetProjectsByUserId

        Dim dtos = New List(Of DtoProject)

        dtos = (From a In context.Projects.Where(Function(a) a.UserId.Contains(userid))
                Select New DtoProject With {.ProjectId = a.ProjectId,
                                            .ClientName = a.ClientName,
                                            .ProjectName = a.ProjectName,
                                            .Technology = a.Technology,
                                            .ProjectType = a.ProjectType,
                                            .UserId = a.UserId,
                                            .StartDate = a.StartDate,
                                            .EndDate = a.EndDate,
                                            .Cost = a.Cost}).ToList()
       

        Return dtos

    End Function

    Public Sub CreateProject(ByVal dto As DtoProject) Implements IDaoProject.CreateProject

        Dim project = New Project() With {.ClientName = dto.ClientName,
                                            .ProjectName = dto.ProjectName,
                                            .Technology = dto.Technology,
                                            .ProjectType = dto.ProjectType,
                                            .UserId = dto.UserId,
                                            .StartDate = dto.StartDate,
                                            .EndDate = dto.EndDate,
                                            .Cost = dto.Cost}
        context.Projects.Add(project)
        context.SaveChanges()

       
    End Sub

    Public Sub UpdateProject(ByVal dto As DtoProject) Implements IDaoProject.UpdateProject

        Dim project = New Project()
       
        project = (context.Projects.Where(Function(a) a.ProjectId = dto.ProjectId)).SingleOrDefault()
       
        If Not IsNothing(project) Then
            project.ClientName = dto.ClientName
            project.ProjectName = dto.ProjectName
            project.Technology = dto.Technology
            project.ProjectType = dto.ProjectType
            project.UserId = dto.UserId
            project.StartDate = dto.StartDate
            project.EndDate = dto.EndDate
            project.Cost = dto.Cost
        End If

      
        If IsNothing(project) Then
            Exit Sub
        End If

        context.Entry(project).State = EntityState.Modified
        context.SaveChanges()
       
    End Sub

    Public Sub DeleteProject(ByVal id As Int32) Implements IDaoProject.DeleteProject

        Dim project As Project
        
        project = (context.Projects.Where(Function(a) a.ProjectId = id)).Include("Tasks").SingleOrDefault()
       
        If IsNothing(project) Then
            Exit Sub
        End If

        For i As Integer = 0 To  project.Tasks.Count - 1
            Dim task = project.Tasks(i)
            context.Entry(task).State = EntityState.Deleted
        Next
        
        context.Entry(project).State = EntityState.Deleted
        context.SaveChanges()
       
    End Sub

    End Class

Public Class DtoProject

    Public Property ProjectId As Int32
    Public Property ClientName As String
    Public Property ProjectName As String
    Public Property Technology As String
    Public Property ProjectType As String
    Public Property UserId As String
    Public Property StartDate  As DateTime
    Public Property EndDate As DateTime? 
    Public Property Cost As Decimal
   
End Class