建立EF访问数据库架构时，出现One or more validation errors were detected during model generation

原因是因为我在写实体类的时候没有为实体类中的属性声明一个主键，即用[key]特性标注在属性上，这样DbContext才能为我们在数据库上找到对应的主键

using System.ComponentModel.DataAnnotations.Schema;
using System.ComponentModel.DataAnnotations;
using System;
namespace Feng.Entity
{
    [Serializable]
    [Table("dict_sample")]
    public class Dict_sample
    {
        [Key]//必须要添加的特性，要和数据库主键对应
        [Column("sam_id")]
        [StringLength(12)]
        public string Sam_id
        { get; set; }

        [Column("sam_name")]
        [StringLength(50)]
        public string Sam_name
        { get; set; }

        [StringLength(18)]
        [Column("sam_code")]
        public string Sam_code
        { get; set; }

        [StringLength(12)]
        [Column("sam_incode")]
        public string Sam_incode
        { get; set; }

        [StringLength(12)]
        [Column("sam_type")]
        public string Sam_type
        { get; set; }

        [StringLength(18)]
        [Column("sam_py")]
        public string Sam_py
        { get; set; }

        [StringLength(18)]
        [Column("sam_wb")]
        public string Sam_wb
        { get; set; }

        [Column("sam_seq")]
        public int Sam_seq
        { get; set;
        }

        [StringLength(1)]
        [Column("sam_del")]
        public string Sam_del
        { get; set; }

        [StringLength(18)]
        [Column("sam_custom_type")]
        public string Sam_custom_type
        { get; set; }

        [StringLength(100)]
        [Column("sam_trans_code")]
        public string Sam_trans_code
        { get; set; }

    }
}