EntityType 没有键定义错误

Question

Controller:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using MvcApplication1.Models;
using System.ComponentModel.DataAnnotations.Schema;

namespace MvcApplication1.Controllers
{
    public class studentsController : Controller
    {
        //
        // GET: /students/

        public ActionResult details()
        {
            int id = 16;
            studentContext std = new studentContext();
           student first = std.details.Single(m => m.RollNo == id);
            return View(first);
        }

    }
}

DbContext Model:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Data.Entity;

namespace MvcApplication1.Models
{
    public class studentContext : DbContext
    {
        public DbSet<student> details { get; set; }
    }
}

Model:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.ComponentModel.DataAnnotations.Schema;

namespace MvcApplication1.Models
{
    [Table("studentdetails")]
    public class student
    {
        public int RollNo;
        public string Name;
        public string Stream;
        public string Div;
    }
}

Database table:

CREATE TABLE [dbo].[studentdetails](
    [RollNo] [int] NULL,
    [Name] [nvarchar](50) NULL,
    [Stream] [nvarchar](50) NULL,
    [Div] [nvarchar](50) NULL
)  

In global.asax.cs

Database.SetInitializer<MvcApplication1.Models.studentContext>(null);

The above code lists all the classes I am working on. Upon running my application am receiving the error:

"One or more validation errors were detected during model generation" along with "Entity type has no key defined".

Answer 1

The Model class should be changed to :

using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.ComponentModel.DataAnnotations.Schema;
using System.ComponentModel.DataAnnotations;

namespace MvcApplication1.Models
{
    [Table("studentdetails")]
    public class student
    {
        [Key]
        public int RollNo { get; set; }

        public string Name { get; set; }

        public string Stream { get; set; }

        public string Div { get; set; }
    }
}

Answer 2

1. Make sure public members of student class are defined as properties w/ {get; set;} {get; set;} (yours are public variables - a common mistake).

2. Place a [Key] annotation on top of your chosen property.

Answer 3

There are several reasons this can happen. Some of these I found here , others I discovered on my own.

• If the property is named something other than Id , you need to add the [Key] attribute to it.
• The key needs to be a property, not a field.
• The key needs to be public
• The key needs to be a CLS-compliant type, meaning unsigned types like uint , ulong etc. are not allowed.
• This error can also be caused by configuration mistakes .

Answer 4

i know that this post is late but this solution helped me:

    [Key]
    [Column(Order = 0)]
    public int RoleId { get; set; }

added [Column(Order = 0)] after [Key] can be added by increment by 1:

    [Key]
    [Column(Order = 1)]
    public int RoleIdName { get; set; }

etc...

Answer 5

In my case, I was getting the error when creating an "MVC 5 Controller with view, using Entity Framework".

I just needed to Build the project after creating the Model class and didn't need to use the [Key] annotation.

Answer 6

Using the [key] didn't work for me but using an id property does it. I just add this property in my class.

public int id {get; set;}

Answer 7

The object must contain a field which will be used as the Primary Key , if you have a field named Id then this will by default be the primary key of the object to which Entity Framework will link to.

Otherwise, you should add the [Key] attribute above that field you wanna use as the Primary Key , and you'll also need to add the namespace System.ComponentModel.DataAnnotations :

public class myClass
{
    public int Id { get; set; }
    [Key]
    public string Name { get; set; }
}

https://stackoverflow.com/a/51180941/7003760

Answer 8

Additionally Remember, Don't forget to add public keyword like this

[Key] 
int RoleId { get; set; } //wrong method

you must use Public keyword like this

[Key] 
public int RoleId { get; set; } //correct method

Answer 9

The reason why EF framework prompt 'no key' is that EF framework needs a primary key in database. To declaratively tell EF which property the key is, you add a [Key] annotation. Or, the quickest way, add an ID property. Then, the EF framework will take ID as the primary key by default.

Answer 10

For me, the model was fine. It was because I had 2 different versions of entity framework. One version for the web project and another one for the common project which contains the models.

I just had to consolidate the nuget packages .

Enjoy!

Answer 11

You don't have to use key attribute all the time. Make sure the mapping file properly addressed the key

this.HasKey(t => t.Key);
this.ToTable("PacketHistory");
this.Property(p => p.Key)
            .HasColumnName("PacketHistorySK");

and don't forget to add the mapping in the Repository's OnModelCreating

modelBuilder.Configurations.Add(new PacketHistoryMap());

Answer 12

All is right but in my case i have two class like this

namespace WebAPI.Model
{
   public class ProductsModel
{ 
        [Table("products")]
        public class Products
        {
            [Key]
            public int slno { get; set; }

            public int productId { get; set; }
            public string ProductName { get; set; }

            public int Price { get; set; }
}
        }
    }

After deleting the upper class it works fine for me.

Answer 13

I too solved this issue in my own project by solving this particular line in my code. I added the following.

[DatabaseGenerated(DatabaseGeneratedOption.None)]

After realizing my mistake I then went and changed it to

[DatabaseGenerated(DatabaseGeneratedOption.Identity)]

This further ensures that the field named "Id" increments in value each time a new row is inserted in the database