我为一个类似 Google Forms 的项目建模。下面的实体非常简单明了(我猜),如下所示。
问题类型:
// Base class for any kind of question
public abstract class Question : Bean
{
public string Statement { get; set; }
}
// Visual questions are questions where images are answers.
public class VisualQuestion : Question
{
public virtual VisualAnswer Answer { get; set; }
}
// Discursive questions are questions where big texts are answers.
public class DiscursiveQuestion : Question
{
public virtual DiscursiveAnswer Answer { get; set; }
}
// Objective questions are questions that can have multiple answers,
// where each of them should be no bigger than 1 character.
public class ObjectiveQuestion : Question
{
public virtual List<ObjectiveQuestionOption> Options { get; set; }
}
// Options for objective questions.
public class ObjectiveQuestionOption : Question
{
public int ObjectiveQuestionId { get; set; }
public virtual ObjectiveQuestion Question { get; set; }
public virtual ObjectiveAnswer Answer { get; set; }
}
答案类型:
public abstract class Answer : Bean
{
public int QuestionId { get; set; }
}
public class DiscursiveAnswer : Answer
{
public string Answer { get; set; }
public virtual DiscursiveQuestion Question { get; set; }
}
public class ObjectiveAnswer : Answer
{
public char Answer { get; set; }
public virtual ObjectiveQuestion Question { get; set; }
}
public class VisualAnswer : Answer
{
public byte[] Blob { get; set; } // Image answer
public virtual VisualQuestion Question { get; set; }
}
豆在哪里:
public abstract class Bean
{
public int Id { get; set; }
}
对于我可以有的问题,相反,一个Question
对象和一个QuestionOption
用于客观问题。如果是这样,我们将需要Answer
里面的所有 3 个对象Question
,这对我来说听起来不对(需要识别问题类型,然后相应地访问其答案成员,如is
and as
casts)。作为一种解决方法,我决定使用TPH方法将问题分成上面定义的 3 个对象,并拥有单独的 Answer 成员。
一切似乎都只适用于 1 个条件:所有流畅的 API 设置必须在void OnModelCreating(DbModelBuilder modelBuilder)
类中完成DbContext
(我已经覆盖了它)。这是一个问题,因为我正在为每个实体对象分离所有配置并像这样添加它们:
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
// Approach 1: This works
//modelBuilder.Entity<Question>().Map<DiscursiveQuestion>(p => p.Requires("TP_QUESTION").HasValue("D")).ToTable("TB_QUESTION");
//modelBuilder.Entity<Question>().Map<ObjectiveQuestion>(p => p.Requires("TP_QUESTION").HasValue("O")).ToTable("TB_QUESTION");
//modelBuilder.Entity<Question>().Map<VisualQuestion>(p => p.Requires("TP_QUESTION").HasValue("V")).ToTable("TB_QUESTION");
// Approach 2: This does not work: it complains that 2 of the 3 entities cant share the TB_QUESTION table because "they are not in the same type hierarchy
// or do not have a valid one to one foreign key relationship with matching primary keys between them" (???).
modelBuilder.Configurations.Add(new VisualQuestionConfiguration());
modelBuilder.Configurations.Add(new ObjectiveQuestionConfiguration());
modelBuilder.Configurations.Add(new DiscursiveQuestionConfiguration());
}
这些是配置对象:
public abstract class QuestionConfiguration<T> : EntityTypeConfiguration<T> where T : Question
{
public QuestionConfiguration()
{
Property(p => p.Statement).HasColumnName("STATEMENT");
}
}
public class DiscursiveQuestionConfiguration : QuestionConfiguration<DiscursiveQuestion>
{
public DiscursiveQuestionConfiguration()
{
Map(p => p.Requires("TP_QUESTION").HasValue("D")).ToTable("TB_QUESTION");
}
}
public class VisualQuestionConfiguration : QuestionConfiguration<VisualQuestion>
{
public VisualQuestionConfiguration()
{
Map(p => p.Requires("TP_QUESTION").HasValue("V")).ToTable("TB_QUESTION");
}
}
public class ObjectiveQuestionConfiguration : QuestionConfiguration<ObjectiveQuestion>
{
public ObjectiveQuestionConfiguration()
{
Map(p => p.Requires("TP_QUESTION").HasValue("O")).ToTable("TB_QUESTION");
}
}
为什么方法 1 有效,而方法 2 无效?
编辑:
我删除了配置继承,它“几乎”工作(见下文)。像这样:
public class QuestionConfiguration : EntityTypeConfiguration<Question>
{
public QuestionConfiguration()
{
Property(p => p.Statement).HasColumnName("STATEMENT");
// Configures the TPH
Map<VisualQuestion>(p => p.Requires("TYPE").HasValue("Visual").HasMaxLength(10));
Map<ObjectiveQuestion>(p => p.Requires("TYPE").HasValue("Objective").HasMaxLength(10));
Map<DiscursiveQuestion>(p => p.Requires("TYPE").HasValue("Discursive").HasMaxLength(10));
ToTable("TB_QUESTION");
}
}
public class DiscursiveQuestionConfiguration : Configuration<DiscursiveQuestion>
{
public DiscursiveQuestionConfiguration()
{
}
}
public class VisualQuestionConfiguration : Configuration<VisualQuestion>
{
public VisualQuestionConfiguration()
{
}
}
public class ObjectiveQuestionConfiguration : Configuration<ObjectiveQuestion>
{
public ObjectiveQuestionConfiguration()
{
}
}
public class ObjectiveQuestionOptionConfiguration : Configuration<ObjectiveQuestionOption>
{
public ObjectiveQuestionOptionConfiguration()
{
HasRequired(p => p.Question).WithMany(p => p.Options).HasForeignKey(p => p.ObjectiveQuestionId);
Property(p => p.ObjectiveQuestionId).HasColumnName("ID_OBJECTIVE_QUESTION");
Property(p => p.Statement).HasColumnName("STATEMENT"); // <--- This doesnt get mapped! :(
ToTable("TB_OBJECTIVE_QUESTION_OPTION");
}
}
并像这样注册它们:
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
// Approach 1: This works
//modelBuilder.Entity<Question>().Map<DiscursiveQuestion>(p => p.Requires("TP_QUESTION").HasValue("D")).ToTable("TB_QUESTION");
//modelBuilder.Entity<Question>().Map<ObjectiveQuestion>(p => p.Requires("TP_QUESTION").HasValue("O")).ToTable("TB_QUESTION");
//modelBuilder.Entity<Question>().Map<VisualQuestion>(p => p.Requires("TP_QUESTION").HasValue("V")).ToTable("TB_QUESTION");
// Approach 2: This does work too, however ObjectiveQuestionOption* does not inherit the statement column
modelBuilder.Configurations.Add(new QuestionConfiguration());
modelBuilder.Configurations.Add(new QuestionOptionConfiguration());
}