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Mapping Many-To-Many Scenario

Brendan Rice

04 Jul, 2010 02:24 PM via web

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Thanks in advance to anyone that is helping.

I have [Projects] that have [Tasks], both [Projects] and [Tasks] can have a [Context]. If a [Context] name already exists then it is to be used for the Project/Task instead of creating a new one.

When I assign a Context to a Task I get the following error:
a different object with the same identifier value was already associated with the session: 8342e08c-3c77-490e-8b23-9da501880511, of entity: MyNameSpace.Context

Here is how I assign Contexts to Projects and Tasks:

ContextDto taskContextDto = null;

        ContextDto projectContextDto = null;

        if (context == null)
        {
            taskContextDto = new ContextDto { Name = _context };
            projectContextDto = taskContextDto;
        }
        else
        {
            taskContextDto = context;
            projectContextDto = context;
        }

        IProjectWcfService projectWcfService = _projectServiceFactory.Create();

        if (!string.IsNullOrEmpty(_task))
        {
            dto.Tasks.Add(new TaskDto { Name = _task });

            if (!string.IsNullOrEmpty(_context))
            {
                dto.Tasks[0].Contexts = new List<ContextDto> { taskContextDto };
            }
        }

        if (!string.IsNullOrEmpty(_context))
        {
            dto.Contexts.Add(projectContextDto);
        }

---

Here is what my mapping classes look like:

[TASK] public class TaskMap : IAutoMappingOverride

{
    public void Override(AutoMapping<Task> mapping)
    {
        mapping.Table("Tasks");
        //mapping.LazyLoad(SetAttribute("lazy", "false");

        // Evil assigned ID - use identity instead unless you're working with a legacy DB
        mapping.Id(x => x.Id, "TaskID")
            .GeneratedBy
            .GuidComb(); 

        mapping.Map(x => x.Name, "TaskName");

        mapping.Map(x => x.Done, "Done");

        mapping.References<Project>(x => x.Project, "ProjectID")
            .Fetch
            .Join();

        mapping.HasManyToMany<Context>(x => x.Contexts)
            .Table("TaskContexts")
            .ParentKeyColumn("TaskID")
            .ChildKeyColumn("ContextID")
            .Cascade.All()
            .AsBag();
    }
}

}

[PROJECT]

public sealed class ProjectMap : IAutoMappingOverride<Project>
{
    public void Override(AutoMapping<Project> mapping)
    {
        mapping.Table("Projects");

        // Evil assigned ID - use identity instead unless you're working with a legacy DB
        mapping.Id(x => x.Id, "ProjectID")
            .GeneratedBy
            .GuidComb();

        mapping.Map(x => x.Name, "ProjectName");

        mapping.Map(x => x.Done, "Done");

        mapping.References(x => x.User, "UserID");

        mapping.HasManyToMany<Context>(x => x.Contexts)
            .Table("ProjectContexts")
            .ParentKeyColumn("ProjectID")
            .ChildKeyColumn("ContextID")
            .Cascade.All()
            .AsBag();

        mapping.HasMany(x => x.Tasks)
            .KeyColumns.Add("ProjectID")
            .Inverse()
            .Cascade.All()
            .AsBag();
    }
}

---

[CONTEXT]

public class ContextMap : IAutoMappingOverride<Context>
{
    public void Override(AutoMapping<Context> mapping)
    {
        mapping.Table("Contexts");

        // Evil assigned ID - use identity instead unless you're working with a legacy DB
        mapping.Id(x => x.Id, "ContextID")
            .GeneratedBy
            .GuidComb(); 

        mapping.Map(x => x.Name, "ContextName");
    }
}

---

1. Support Staff 2 Posted by Paul Batum on 05 Jul, 2010 12:03 PM

   

   The error you are getting usually indicates that there is something wrong
   with the way you are handling your objects and sessions, rather than your
   mappings. Also, I'm having alot of trouble understanding the code you
   provided because you listed your maps, but the example code is all DTO's,
   not domain objects. Can you explain why?

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2. 3 Posted by Brendan Rice on 05 Jul, 2010 04:23 PM

   

   Hi Paul,

   thanks for the reply. Apologies I should have mentioned I am using S#arp Architecture for the server side code and all it does is open a session per request. I am hitting web services that open the session then everything after that is pretty standard S#arp Architecture i.e. repository.

   Any ideas?

   Thanks again,

   B
   

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3. 4 Posted by Brendan Rice on 05 Jul, 2010 10:29 PM

   

   Here is my server side code:

   SERVICE SAVE

       public ProjectDto Save(ProjectDto projectDto)
       {
           User user = CurrentUser;
   
           // I'd rather have the transaction begun via an attribute, like with a controller action, 
           // or within a service object, but this works for the current example.
           _projectRepository.DbContext.BeginTransaction();
   
           Project project = Project.CreateDomain(projectDto);
           project.User = user;
           project.Tasks.ForEach(x => x.Project = project);
   
           project.Validate();
   
           Project savedProject = project.IsNew ? _projectRepository.Save(project) : _projectRepository.Update(project);
   
           var returnDto = Project.CreateDto(savedProject);
           // Since we're certainly not going to require lazy loading, commit the transcation
           // before returning the data.
           _projectRepository.DbContext.CommitTransaction();
   
           return returnDto;
       }
   

   DOMAIN OBJECT

       public static ProjectDto CreateDto(Project project)
       {
           InitializeMapper();
   
           ProjectDto projectDto = Mapper.Map<Project, ProjectDto>(project);
   
           return projectDto;
       }
   
       public static Project CreateDomain(ProjectDto projectDto)
       {
           InitializeMapper();
   
           Project project = Mapper.Map<ProjectDto, Project>(projectDto);
   
           return project;
       }
   

   Again any help is appreciated.

   B

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4. Support Staff 5 Posted by Paul Batum on 06 Jul, 2010 11:18 AM

   

   Nothing in that most recent batch of code strikes me as odd, but I still
   don't really understand where the exception is happening and how that first
   batch of code you provided relates to everything else.

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5. 6 Posted by Brendan Rice on 06 Jul, 2010 11:39 AM

   

   I think it may have something to do with adding a context twice although I am not sure.

   I really need to dig into it a little further, are there any good debugging tools out there for NH?

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6. Support Staff 7 Posted by Paul Batum on 06 Jul, 2010 12:11 PM

   

   NH Prof is useful but its more for doing performance optimization than
   debugging.

   Usually the way I tackle a problem like this is I try to strip it down, make
   it simpler and simpler until it starts working and then backtrack.

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7. 8 Posted by Brendan Rice on 06 Jul, 2010 10:21 PM

   

   I think I have figured out what was going wrong. Let me explain.

   When I add a new Task to an existing Project and assign it an existing Context that already belong to the project the mapping gets confused as the Context is already assign to a Project and is already therefore in the session.

   How can I go about avoiding this?

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8. Support Staff 9 Posted by Paul Batum on 07 Jul, 2010 10:58 AM

   

   For me personally, this problem is too difficult to remotely debug as its
   currently presented. If you can come up with a version that deals purely
   with domain objects and sessions (not dto's) and still exhibits the problem,
   I'll have a chance of making sense of it. If the problem only occurs in your
   full stack with DTO's in the mix, then I'd suggest that the problem is not
   related to your mappings.

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