无法使用EF DbContext保存更改

Question

我正在从“编程实体框架代码优先”学习EF Code First。以下代码段从第5页复制到第7页。

Visit.cs

using System;

namespace ChapterOne
{
    class Visit
    {
        public int Id { get; set; }
        public DateTime Date { get; set; }
        public String ReasonForVisit { get; set; }
        public String Outcome { get; set; }
        public Decimal Weight { get; set; }
        public int PatientId { get; set; }
    }
}

AnimalType.cs

namespace ChapterOne
{
    class AnimalType
    {
        public int Id { get; set; }
        public string TypeName { get; set; }
    }
}

Patient.cs

using System;
using System.Collections.Generic;

namespace ChapterOne
{
    class Patient
    {
        public Patient()
        {
            Visits = new List<Visit>();
        }
        public int Id { get; set; }
        public string Name { get; set; }
        public DateTime BirthDate { get; set; }
        public AnimalType AnimalType { get; set; }
        public DateTime FirstVisit { get; set; }
        public List<Visit> Visits { get; set; }
    }
}

VetContext.cs

using System.Data.Entity;

namespace ChapterOne
{
    class VetContext : DbContext
    {
        public DbSet<Patient> Patients { get; set; }
        public DbSet<Visit> Visits { get; set; }
    }
}

Program.cs的

using System;
using System.Collections.Generic;

namespace ChapterOne
{
    class Program
    {
        static void Main(string[] args)
        {
            var dog = new AnimalType { TypeName = "Dog" };

            var patient = new Patient
            {
                Name = "Simpson",
                BirthDate = new DateTime(2008, 1, 28),
                AnimalType = dog,
                Visits = new List<Visit> 
                { 
                    new Visit 
                    { 
                        Date = new DateTime(2011, 9, 1)
                    }
                }

            };

            using (var context = new VetContext())
            {
                context.Patients.Add(patient);
                context.SaveChanges();
            }
        }
    }
}

不幸的是，我收到了以下错误。你能告诉我出了什么问题吗？

Answer 1

可能你没有填写所有必填字段。我注意到的是Patient.FirstVisit sql server不接受默认值。

Answer 2

不确定这是否是您确切错误的原因，但也可能导致其他错误;您的VetContext应该还包含1行：

public DbSet<AnimalType> AnimalTypes { get; set; }

否则，EF不会在DB中创建AnimalType表来插入

var dog = new AnimalType { TypeName = "Dog" };

记录到。