ASP.Net MVC 1 to many binding doesn't work

Question

I am new to MVC and I've got this annoying problem.

I am doing a small project to understand MVC better.

I am working in a code-first way.

I've created these two classes:

public class Post
    {
        [Required]
        public int ID { get; set; }

        [Required]
        public string UserName { get; set; }

        [Required]
        public string Title { get; set; }

        [Required]
        public string Text { get; set; }

        [Required]
        [DisplayFormat(DataFormatString = "{0:dd MMM yyyy}")]
        public DateTime Date { get; set; }

        [Required]
        public PostCategoryType Category { get; set; }

        [Required]
        public string PictureUrl { get; set; }

        [Required]
        public string VideoUrl { get; set; }

        public virtual List<UserComment> Comments { get; set; }
    }

public class UserComment
    {
        [Required]
        public int ID { get; set; }
        [Required]
        public string Name { get; set; }
        [Required]
        public string Email { get; set; }
        [Required]
        public string WebSite { get; set; }
        [Required]
        public string Comment { get; set; }
        [Required]
        [DisplayFormat(DataFormatString = "{0:dd MMM yyyy}")]
        public DateTime Date { get; set; }
    }

public class MyStoreDbContext : DbContext
    {
        public DbSet<Post> Posts { get; set; }
        public DbSet<UserComment> UsersComments { get; set; }
    }

in order for the classes to be generated into tables at the entity framework I simply added controllers - one for each class and than ran the program and it generated the two tables.

The generated tables at the entity framework looks like this:

CREATE TABLE [dbo].[Posts] (
    [ID]         INT            IDENTITY (1, 1) NOT NULL,
    [UserName]   NVARCHAR (MAX) NOT NULL,
    [Title]      NVARCHAR (MAX) NOT NULL,
    [Text]       NVARCHAR (MAX) NOT NULL,
    [Date]       DATETIME       NOT NULL,
    [Category]   INT            NOT NULL,
    [PictureUrl] NVARCHAR (MAX) NOT NULL,
    [VideoUrl]   NVARCHAR (MAX) NOT NULL,
    CONSTRAINT [PK_dbo.Posts] PRIMARY KEY CLUSTERED ([ID] ASC)
);



CREATE TABLE [dbo].[UserComments] (
    [ID]      INT            IDENTITY (1, 1) NOT NULL,
    [Name]    NVARCHAR (MAX) NOT NULL,
    [Email]   NVARCHAR (MAX) NOT NULL,
    [WebSite] NVARCHAR (MAX) NOT NULL,
    [Comment] NVARCHAR (MAX) NOT NULL,
    [Date]    DATETIME       NOT NULL,
    [Post_ID] INT            NULL,
    CONSTRAINT [PK_dbo.UserComments] PRIMARY KEY CLUSTERED ([ID] ASC),
    CONSTRAINT [FK_dbo.UserComments_dbo.Posts_Post_ID] FOREIGN KEY ([Post_ID]) REFERENCES [dbo].[Posts] ([ID])
);


GO
CREATE NONCLUSTERED INDEX [IX_Post_ID]
    ON [dbo].[UserComments]([Post_ID] ASC);

I have a controller which have a data member of :

private MyStoreDbContext db = new MyStoreDbContext ();

in which I want my posts and user comments from.

Now to the problem: When I access :

foreach(Post post in db.Posts)
{
  post.Comments <------ This is always null
}

I've tried inserting a record of post with id 1 for example. Than I inserted to the UserComments in which the post_id is the 1. (Both manually with VS Server Explorer); when I try the code above the comments are always null.

I even tried different approach in which I manually inserted at debug time this:

UserComment comment = new UserComment... // Initialization
Post post = new Post.. // Initializing all but Comments
post.Comments = new List<UserComment>();
post.Comments.Add(comment);
db.Comments.Add(comment);
db.Posts.Add(post);
db.SaveChanges();

After all that, each and every post's comments property is null.

What am I missing? Please help me as it is driving me crazy and accroding to other people's solutions to this problem online is exactly like this I cannot point out the problem.

Thanks in advance to all the helpers!

Answer 1

You need to add ID of Post in the UserComment class, like below:

public class UserComment
    {
        [Required]
        public int ID { get; set; }
        [Required]
        public string Name { get; set; }
        [Required]
        public string Email { get; set; }
        [Required]
        public string WebSite { get; set; }
        [Required]
        public string Comment { get; set; }
        [Required]
        [DisplayFormat(DataFormatString = "{0:dd MMM yyyy}")]
        public DateTime Date { get; set; }  

        public int PostID { get; set; }

       [ForeignKey("PostID")]
       public virtual Post Post { get; set; }       

    }

Then, Create a instance of Post first, like below:

var newPost = new Post{
   UserName = "John",
   //
}

db.Posts.Add(newPost );
db.SaveChanges();

After that, create a instance of UserComment , assign the ID of newPost to it, see below:

var comment  = new UserComment
{
   Name  = "Some one",
   //
   PostID = newPost.ID
}
newPost.Comments.Add(comment);
db.SaveChanges();

Note: You can learn more about this at below link:

http://codeblog.shawson.co.uk/entity-framework-4-1-code-first-with-one-to-many-relationship-code-example/