实体框架主键异常

Question

I have a very simple C# class, which contains one primary key. I am using EF 6 with code-first and I have two questions:

1. How do I make a primary key as an Identity in code-first (and how to not make it an identity)? Some of my classes need the PK to be an identity (auto increment on addition) and some need it to be assigned by code.

2. When I try to save the class to the database using:

    // This code is actually wrapped by a BusinessContext Class to encapsulate the ORM representation context.Costumers.Add(costumer); //exception is here! context.SaveChanges(); 

   I get the following exception for my class, on the Add method:

   One or more validation errors were detected during model generation:

   M.Costumer: : EntityType 'Costumer' has no key defined. Define the key for this EntityType.
   Costumers: EntityType: EntitySet 'Costumers' is based on type 'Costumer' that has no keys defined.

and this is the class itself:

using Microsoft.Practices.Prism.Mvvm;
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace MyApp.Models
{
    public class Costumer : BindableBase
    {
        private string name;
        private string city;
        private Estado state;
        private int costumerId;

        [Required]
        [StringLength(500)]        
        public string Name
        {
            get { return this.name; }
            set { SetProperty(ref name, value); }
        }

        [Required]
        [StringLength(500)]
        public string City
        {
            get { return this.city; }
            set { SetProperty(ref city, value); }
        }

        [Required]
        public State State
        {
            get { return this.state; }
            set { SetProperty(ref state, value); }
        }

        [Required]
        [Key]
        public int CostumerId
        {
            get { return this.costumerId; }            
        } 
    }
}

The class does have a [Key] , so how come there is an exception saying there isn't a key?

Answer 1

Entity Framework must have a getter and a setter for any [Key] attributes.

If you want to designate to EF that you will be generating the values for this field, you can use [DatabaseGeneratedOption.None] .

the DatabaseGeneratedOption Enumeration has 3 different values:

• Computed -- The database generates a value when a row is inserted or updated.
• Identity -- The database generates a value when a row is inserted.
• None -- The database does not generate values.

The default for a key value is DatabaseGeneratedOption.Identity

Answer 2

在密钥中使用[DatabaseGeneratedOption.None]属性。