EF实例问题.做到一半.提示未将引用设置到对象的实例.

[sugarbelle]

 class Question
    {
        public int Id { get; set; }
        public string Content { get; set; }

        public virtual ICollection<Answer> Answers { get; set; }
    }

    class Answer
    {
        public int Id { get; set; }
        public string Content { get; set; }

        public virtual Question Question { get; set; }
    }
    class AnswersContext : DbContext
    {
        public DbSet<Question> Questions { get; set; }
        public DbSet<Answer> Answers { get; set; }
    }
    internal class Program
    {
        static void Main(string[] args)
        {
            DoWork();

            Console.WriteLine("Press any key to exit...");
            Console.ReadKey();
        }

        static void DoWork()
        {
            Console.WriteLine("===Please enter five Questions and Answers===");
            for (int i = 0; i < 5; i++)
            {
                Console.WriteLine("Enter the Question:");
                string question = Console.ReadLine();
                Console.WriteLine("Enter the Answer:");
                string answer = Console.ReadLine();
                Console.WriteLine("Saving entry...");
                SaveInput(question, answer);
            }
            PrintQuestions();
        }


        private static void SaveInput(string question, string answer)
        {
            using (var ctx = new AnswersContext())
            {
                ctx.Questions.Add(new Question()
                {
                    Content = question,
                    Answers = { new Answer() { Content = answer } }
                });
                ctx.SaveChanges();
            }
        }

        private static void PrintQuestions()
        {
            using (var ctx = new AnswersContext())
            {
                foreach (var q in ctx.Questions)
                {
                    Console.WriteLine(q.Content);
                    foreach (var a in q.Answers)
                    {
                        Console.WriteLine(" -" + a.Content);
                    }
                }
            }
        }

原文地址:
http://msdn.microsoft.com/en-us/data/jj819165
运行到 ctx.Questions.Add( 就提示未将引用设置到对象的实例了.以往这提示一般是某个对象是null的未实例化.
但我断点看都有数据呀.只是数据库好像没有生成.
1.EF的code first是要到什么步骤才会生成数据库?(实例文章上说写好类就按F5,main方法里还是空的.我按了也没生成)
2.这个错误是我哪里错了?大神指教下.谢谢
(我环境是vs2012+.net4.5+EF6最新装的)

[q107770540]

因为你引用的外键表Answer是空的

 private static void SaveInput(string question, string answer)       
 {           
 	using (var ctx = new AnswersContext())            
	{                
               var answer=new Answer() { Content = answer };
               ctx.SaveChanges();    
		ctx.Questions.Add(new Question()                
			{                   
 				Content = question,                  
  				Answers = { answer },              
  			});                
		ctx.SaveChanges();       
        }    
  }

[q107770540]

[quote=引用 楼主 sugarbelle 的回复:] (我环境是vs2012+.net4.5+EF6最新装的) quote] 据我所知，目前EF最新的才 到EF5吧。。。

[q107770540]

 private static void SaveInput(string question, string answer)       
 {           
 	using (var ctx = new AnswersContext())            
	{                
               var answer=new Answer() { Content = answer };
               ctx.Answers.Add(answer);  //////  :(
               ctx.SaveChanges();    
		ctx.Questions.Add(new Question()                
			{                   
 				Content = question,                  
  				Answers = { answer },              
  			});                
		ctx.SaveChanges();       
        }    
  }

[sugarbelle]

引用 3 楼 q107770540 的回复:

C# code?123456789101112131415 private static void SaveInput(string question, string answer) { using (var ctx = new AnswersContext()) { ……

还是同样提示.
这次我看到 answer里面的question是null的.

[sugarbelle]

引用 2 楼 q107770540 的回复:

Quote: 引用 楼主 sugarbelle 的回复: (我环境是vs2012+.net4.5+EF6最新装的) quote] 据我所知，目前EF最新的才 到EF5吧。。。

nuget里输入:Install-Package EntityFramework -Pre 默认装的是ef6 -alpha3