“存储更新，插入或删除语句影响了意外的行数（0）

Question

我正在使用EF将简单对象插入db：

public bool AddQuestion(Question question)
{
    try
    {
        _ctx.Questions.Add(question);

        _ctx.SaveChanges();
        return true;
    }
    catch(Exception ex)
    {
        return false;
    }
}

我的DbContext看起来像：

 public class AnyContext:DbContext
 {
    public AnyContext():base()
    {
        Configuration.ProxyCreationEnabled = false;
        Configuration.LazyLoadingEnabled = false;

        Database.SetInitializer(new MigrateDatabaseToLatestVersion<AnyContext, AnyContextMigrationConfiguration>());
    }
    public AnyContext(string connectionString)
        : base(connectionString)
    {
         Configuration.ProxyCreationEnabled = false;
         Configuration.LazyLoadingEnabled = false;

         Database.SetInitializer(new MigrateDatabaseToLatestVersion<AnyContext, AnyContextMigrationConfiguration>());
    }
     public DbSet<Question> Questions { get; set; }
 }

POCO看起来像：

[Table("Questions")]
public class Question
{
    public int Id  { get; set; }
    public String body { get; set; }
    public String img_path { get; set; }
    public int location { get; set; }
    public int status { get; set; }
    public DateTime ask_date { get; set; }

}

我得到* “存储更新，插入或删除语句每次都会影响意外的行数（0）。*

我做错了什么？