Linq to SQL通用存储库模式更新问题

Question

I have a weird problem. I am using Generic Repository pattern and Linq to SQL. I have many to many relations between objects which are dbml generated objects and here is the problem. I am getting an error when I try to update the Player object. The error occures when I try to update name of player's skill. This is the exception I'm getting:

An exception of type 'System.InvalidOperationException' occurred in System.Data.Linq.dll but was not handled in user code

Additional information: An attempt was made to remove a relationship between a Skill and a PlayerSkill. However, one of the relationship's foreign keys (PlayerSkill.Skill_ID) cannot be set to null.

Here is the Update method.

 public void Update(PlayerEntity player)
    {
        Player p = Mapper.Map<PlayerEntity, Player>(player);
        _unitOfWork.SkillRepository.AddOrUpdate(p.PlayerSkills.Select(i => i.Skill).ToList());
        _unitOfWork.ProfileRepository.AddOrUpdate(p.Profile);
        _unitOfWork.SocialAccountRepository.AddOrUpdate(p.SocialAccount);
        _unitOfWork.PlayerRepository.AddOrUpdate(p);
    }

AddOrUpdate method on repo:

public void AddOrUpdate(ICollection<TEntity> entities)
    {
        foreach (var e in entities)
        {
            AddOrUpdate(e);
        }
    }

public void AddOrUpdate(TEntity entity)
    {
        if (GetPrimaryKeyValue(entity) > 0)
        {
            Update(entity);
        }
        else
        {
            Insert(entity);
        }
    }

Update method on DataLINQ layer

public void Update(TEntity entity)
    {
        if (entity == null)
        {
            throw new ArgumentNullException("entity");
        }

        var original = GetById(GetPrimaryKeyValue(entity));

        ApplyChanges(original, entity);

        _context.SubmitChanges();
    }

Lastly; ApplyChanges

private void ApplyChanges<F, S>(F originalEntity, S newEntity)
    {
        var entityType = typeof(F);
        var entityProperties = entityType.GetProperties();
        foreach (var propertyInfo in entityProperties)
        {
            var currentProperty = entityType.GetProperty(propertyInfo.Name);
            currentProperty.SetValue(originalEntity, propertyInfo.GetValue(newEntity, null));
        }
    }

I call the object as follows:

public IHttpActionResult PutPlayer(int id, PlayerEntity player)
    {
        if (player == null)
        {
            return NotFound();
        }
        _playerService.Update(player);

        return Ok();
    }

Note: I use AutoMapper to map the objects, but I don't think that is related with error. Thanks in adv.

Answer 1

The problem is that your method ApplyChanges copies too many properties. You want it to copy scalar properties only, ie properties of type int , string , etc., not references and collections. But your method does all of them.

This causes LINQ-to-SQL to conclude that PlayerSkills is replaced by a brand new collection of PlayerSkill objects. So it will try to insert new ones. But it will also try to orphan the existing ones. That causes the exception that PlayerSkill.Skill_ID can't be set to null.

The solution is to copy scalar properties only:

private void ApplyChanges<F, S>(F originalEntity, S newEntity)
{
    var entityType = typeof(F);
    var entityProperties = entityType.GetProperties();
    foreach (var propertyInfo in entityProperties
        // Filter scalar properties
        .Where(pi => pi.PropertyType.IsValueType || pi.PropertyType == typeof(string)))
    {
        var currentProperty = entityType.GetProperty(propertyInfo.Name);
        currentProperty.SetValue(originalEntity, propertyInfo.GetValue(newEntity, null));
    }
}

This filters value-type properties and string properties(string is not a value type but a class).