Entity Framework: Adding entity with relation, a new entity is created

Question

I'm having a serious issue with Entity Framework and I can't tackle it down. I have 2 entities, a chapter and a header, the header is linked to a chapter by using navigation properties.

[Table("T_CHAPTER")]
public class Chapter : EntityBase<int>
{
    [Required]
    [Column(Order = 1)]
    public string Name { get; set; }
}

[Table("T_HEADER")]
public class Header : EntityBase<int>
{
    [Required]
    [Column(Order = 1)]
    public string Name { get; set; }

    [Required]
    [Column(Order = 2)]
    public virtual Chapter Chapter { get; set; }
}

So far, nothing excotic here. Now, I want to tell that I'm using a Unit Of Work and a repository pattern, but I don't think that does mind.

First I'll add a record in the Chapters if it doesn't exists, that done with this code:

private Chapter CreateChapter(string chapter)
{
    var retrievedChapter = UnitOfWork.ChapterRepository.Get(x => x.Name.Equals(chapter, StringComparison.InvariantCultureIgnoreCase));

    if (retrievedChapter == null)
    {
        UnitOfWork.ChapterRepository.Insert(new Chapter { Name = chapter });
        UnitOfWork.Commit();

        retrievedChapter = UnitOfWork.ChapterRepository.Get(x => x.Name.Equals(chapter, StringComparison.InvariantCultureIgnoreCase));
    }

    return retrievedChapter;
}

The Insert method is the following:

public virtual void Insert(TEntity entity)
{
    if (OnBeforeEntityInsert != null)
    { OnBeforeEntityInsert(this, new RepositoryEventArgs(typeof(TEntity), entity)); }

    DbSet.Add(entity);

    if (OnEntityInsert != null)
    { OnEntityInsert(this, new RepositoryEventArgs(typeof(TEntity), entity)); }
}

And here's the Commit method:

public void Commit()
{
    if (OnBeforeCommit != null)
    { OnBeforeCommit(this, EventArgs.Empty); }

    RepositoriesContexts.Each(context => context.SaveChanges());

    if (OnCommit != null)
    { OnCommit(this, EventArgs.Empty); }
}

Each UnitOfWork has it's own context instance, and all the instances are saved here.

Then I do create a header with the following code:

private Header CreateHeader(Chapter chapter, string header)
{
    var retrievedHeader = UnitOfWork.HeaderRepository.Get(x => x.Name.Equals(header, StringComparison.InvariantCultureIgnoreCase) &&
                                                            x.Chapter.Id == chapter.Id);

    if (retrievedHeader == null)
    {
        UnitOfWork.HeaderRepository.Insert(new Header { Name = header, Chapter = chapter });
        UnitOfWork.Commit();

        retrievedHeader = UnitOfWork.HeaderRepository.Get(x => x.Name.Equals(header, StringComparison.InvariantCultureIgnoreCase) &&
                                                            x.Chapter.Id == chapter.Id);
    }

    return retrievedHeader;
}

Now, let's say that I add a chapter through this method and the ID of the created chapter is 1. I then pass that chapter to the header, but here instead of creating a header with the correct chapter, a new chapter is added and linked to the created header.

It's driving me nuts.

Maarten · Accepted Answer · 2014-10-06 13:40:58Z

2

Each UnitOfWork has it's own context instance, and all the instances are saved here.

You have to share a single context across all repositories.

answered Oct 6, 2014 at 13:40

Maarten

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5 Comments

Complexity Over a year ago

Isn't the basic idea of a UnitOfWork that each repository has it's own context instance?

Scott Chamberlain Over a year ago

@Complexity no, the basic idea of UnitOfWork is to tie a bunch of repositories together in to a single manageable context instance. DbContext is already a unit of work style class. You may want to abstract it in the form of a interface to expose it to your consumers, but with EF you should not need a 2nd unit of work layer on top of it.

Maarten Over a year ago

AFAIK, no. The idea of the unit of work pattern is that you can 'write' a single piece of work which contains all inserts, updates, and deletes, in a single action, the commit.

Complexity Over a year ago

@ScottChamberlain thanks for your answer, but it there any drawback when implementing my own UnitOfWork over the DbContext instance?

Scott Chamberlain Over a year ago

@Complexity the only drawback I see is you are re-inventing the wheel, why write a UnitOfWork when EF gives you a UnitOfWork pre-made.

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