C＃实体框架代码首次创建控制器

Question

I want to learn Entity Framework Code First but I can't solve a problem. When I want to create a controller (form Model class Anime using AnimeDbContext) I have error Image Of Error

I see that is some problem with Foreign Key but I dont know why. Here is a code of class Anime

namespace MyBD.Models
{
    [Table("Anime")]

    public class Anime
    {


        [Key] // ustawiamy klucz główny tabeli
        public int Id { get; private set; }
        [Required]
        public string Title { get; private set; }
        public string Description { get; private set; }

        public Anime(int id=0, string title="New", string description="Description") 
        {
            this.Id = id;
            this.Title = title;
            this.Description = description;
        }



        public virtual ICollection<CommentAnime>  Comments { get; set; }


    }

}

And class AnimeComment

    namespace MyBD.Models
{
    [Table("CommentAnime")]
    public class CommentAnime
    {
        [Key]
        public int Id { get; private set; }
        [ForeignKey("anime")] // ustawiamy klucz obcy
        [Required]
        public int AnimeId { get; set; }
        public string Opinion { get; private set; }
        public int Mark { get; private set; }

        public CommentAnime(int id=0, string opinion="My Opinion", int mark=0)
        {
            this.Id = id;
            this.Opinion = opinion;
            this.Mark = mark;
        }

        public virtual Anime anime { get; set; }

Answer 1

Phillip's answer already cover most of the changes you need in your model. I just want to work more on that and provide you with how you can configurate your dbContext class using the FluentAPI. This way you can skip the Data Annotation attributes on your classes:

Anime Class:

public class Anime
{
    public int Id { get; set; }
    public string Title { get; set;}
    public string Description { get; set; }

    public virtual ICollection<CommentAnime> Comments { get; set; }
}

public class CommentAnime
{

    public int Id { get; set; }
    public string Opinion { get; set; }
    public int Mark { get; set; }

    public int AnimeId { get; set; }
    public virtual Anime anime { get; set; }
}

AnimeDbContext class

//Program Table
//Title Field
modelBuilder.Entity<Anime>()
            .Property(t => t.Title)
            .HasColumnType("varchar")
            .HasMaxLength(120) //define some Length..
            .IsRequired(); //Will be translated as Not Null


//CommentAnime
//Opinion Field
modelBuilder.Entity<CommentAnime>()
            .Property(t => t.Opinion)
            .HasColumnType("varchar")
            .HasMaxLength(120) //define some Length..
            .IsRequired(); //Will be translated as Not Null


//Configuring the One-to-Many Relationship

modelBuilder.Entity<CommentAnime>()
            .HasRequired(t => t.Anime)
            .WithMany(x => x.Comments)
            .HasForeignKey(t => t.AnimeId);

If you want to have a nullable ForeinKey in CommentAnime, you can use HasOptional instead of HasRequired . Note that you also don't need to create configuration for your Id columns, since EF use naming conventions

This way your POCO classes are clean and independent of any EF configuration. All database modeling are centralized in the AnimeDbContext class. I personally find this to be the best approach since you avoid poluting your classes with attributes, but, I guess this is just a personal thing.

Answer 2

In entity framework I've found that if any property in your class is called "Id", in upper or lower case, "ID" or "id", it will reference that as the Primary Key. So you don't need the [Key] Data annotation.

You also don't need the [Table()] data annotation, as EF will default to the class name for the table name.

You also don't need to put in a Public Constructor, as you can use the View to set placeholder text. You can use the default constructor for default values, like setting the date created, see Anime class for example.

See below for your new classes.

public class Anime
{
    public Anime()
    {
        Description = "This is a desciption";
        DateCreated= DateTime.UtcNow;

    }

    public int Id { get; set; }
    [Required]
    public string Title { get; set; }
    public string Description { get; set; }
    public DateTime DateCreated { get; set; }      


    public virtual ICollection<CommentAnime>  Comments { get; set; }


}

When doing joins in EF by referencing the parent table as a virtual and using the "nameId" EF again will automatically work it out for you.

public class CommentsAnime
{
    public int Id { get; set; }
    public int AnimeId { get; set; } //Using the virtual table name
    public string Opinion { get; private set; }
    public int Mark { get; private set; }

    public virtual Anime Anime { get; set; }

}