实体框架，以多对多关系发布保存数据

Question

I have issue saving data in many-to-may relationship between two tables that breaks by introducing another table in between, containing primary keys of both. I have code first existing database approach along with repository pattern and unit of work in MVC application

and here is my model classes

Navigation_Functions

public class Navigation_Functions
{
    public Navigation_Functions()
    {

    }
    [Key]
    public int Function_ID { get; set; }

    [StringLength(250)]
    [Required(ErrorMessage = "Required Title")]
    [Display(Name = "Function Title")]
    public string FunctionName { get; set; }

    [Required(ErrorMessage = "Required Hierarchy Level")]
    [Display(Name = "Hierarchy Level")]
    public int Hierarchy_Level { get; set; }

    public ICollection<Navigation_FunctionController> Navigation_FunctionController { get; set; }
  }
}

Navigation_FunctionController Model

 public class Navigation_FunctionController
{
    public Navigation_FunctionController()
    {

    }

    [Key]
    public int ControllerID { get; set; }

    [StringLength(250)]
    [Required]
    public string ControllerName { get; set; }

   public ICollection <Navigation_Functions> Navigation_Functions { get; set; }

}

Junction Model

 [Table("Navigation_FunctionInController")]
public class Navigation_FunctionInController
{
    public Navigation_FunctionInController() 
    { 

    }

    [Key]
    public int FunctionInController_ID { get; set; }

    [Key]
    [ForeignKey("Navigation_Functions")]
    public int Function_ID { get; set; }

    [Key]
    [ForeignKey("Navigation_FunctionController")]
    public int ControllerID { get; set; }

    public Navigation_FunctionController Navigation_FunctionController { get; set; }
    public Navigation_Functions Navigation_Functions { get; set; }

}

I have generic repository for CRUD operation

public void InsertEntity(TEntity obj)
    {
        _DbSet.Add(obj);
    }

My ViewModel

public class FunctionsNavigation_ViewModel 
{
    public Navigation_Functions _Navigation_Functions { get; set; }

    public Navigation_FunctionController _Navigation_FunctionController { get; set; }
}

---

 public void CreateFunctionNavigation(FunctionsNavigation_ViewModel _obj)
  {
    using (var _uow = new FunctionsNavigation_UnitOfWork())
        {
            try
            {                  
                var _navigationFunction = _obj._Navigation_Functions;

               _navigationFunction.Navigation_FunctionController = new List<Navigation_FunctionController>();

               _navigationFunction.Navigation_FunctionController.Add(_obj._Navigation_FunctionController);

               _uow.Navigation_Functions_Repository.InsertEntity(_navigationFunction);

               _uow.Save(); 
            }
            catch
            {

            }
        }
    }

if I remove following line from above code then it save new Navigation_Functions

 _navigationFunction.Navigation_FunctionController.Add(_obj._Navigation_FunctionController);

following is screen shot from debug code.

I am wondering if my ViewModel are correct? secondly How Entity Framework knows that it need to put primary keys of two tables in Navigation_FunctionInController?

Answer 1

When your model looks like this...

public class Navigation_Functions
{
    ...
    public ICollection<Navigation_FunctionController> Navigation_FunctionController { get; set; }
}

public class Navigation_FunctionController
{
    ...
    public ICollection <Navigation_Functions> Navigation_Functions { get; set; }
}

...so without a Navigation_FunctionInController class, the junction table in the database ( Navigation_FunctionInController ) is not represented in the class model. If you have this model code first, EF will create a junction table itself. If you work database first, EF won't create a junction class and in the diagram you will see a pure many to many association, like this: *--* . But this only happens if the junction table only contains the two foreign keys, both of which comprise a compound primary key.

In your model you have an explicit junction class (probably because the table has a primary key field besides the two foreign keys). This means that the many to many association turns into a 1:n:1 association. The class model should essentially look like this...

public class NavigationFunction
{
    ...
    public ICollection<NavigationFunctionInController> NavigationFunctionInControllers { get; set; }
}

public class NavigationFunctionController
{
    ...
    public ICollection <NavigationFunctionInController> NavigationFunctionInControllers { get; set; }
}

public class NavigationFunctionInController
{
    public int FunctionInControllerID { get; set; }

    [ForeignKey("NavigationFunction")]
    public int FunctionID { get; set; }

    [ForeignKey("NavigationFunctionController")]
    public int ControllerID { get; set; }

    public NavigationFunctionController NavigationFunctionController { get; set; }
    public NavigationFunction NavigationFunction { get; set; }

}

Note that the foreign key fields don't have to be part of the primary key (also not that I prefer the singular name Navigation_Function and plural names for collections, and no underscores in names).

So what happens in your code is that you have a 1:n:1 association, but you try to manage it like a m:n association by adding items directly to _navigationFunction.Navigation_FunctionController (s) . But EF doesn't track that collection, and the items are not saved.

Instead you have to create a junction class instance...

var nfic = new NavigationFunctionInController
            {
                NavigationFunction = obj.NavigationFunction,
                NavigationFunctionController = obj.Navigation_FunctionController
            };

...and save it through your repositories and UoW.