无法在 EF 6 上使用 Fluent API 创建 TPH

Question

我正在为一个 Google 类似表单的项目建模。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; }
}

Bean 所在位置：

public abstract class Bean 
{
    public int Id { get; set; }
}

对于问题，我可以有一个 Question 对象和一个 QuestionOption 用于 objective 问题。如果是这样，我们将需要 Question 中的所有 3 个 Answer 对象，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，例如 is 和 as 转换）。作为解决方法，我决定使用 TPH 方法将问题拆分为上面定义的 3 个对象，并拥有单独的 Answer 成员。

一切似乎只在 1 个条件下工作：所有流畅的 API 设置必须在 DbContext class 的 void OnModelCreating(DbModelBuilder modelBuilder) 内完成（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我的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：

我删除了配置继承并且它 "almost" 有效（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());
}

Answer 1

不同之处在于，第一种方法告诉 EF 将基础抽象 class Question 视为实体（modelBuilder.Entity<Question>() 调用），而第二种方法则不然。

您需要为 Question 创建并注册一个单独的配置。由于您将在那里配置所有通用属性，因此 QuestionConfiguration<T> class 是多余的。

这是第二种方法的正确实现。

配置：

public class QuestionConfiguration : EntityTypeConfiguration<Question>
{
    public QuestionConfiguration()
    {
        Property(p => p.Statement).HasColumnName("STATEMENT");
        ToTable("TB_QUESTION");
    }
}

public class DiscursiveQuestionConfiguration : EntityTypeConfiguration<DiscursiveQuestion>
{
    public DiscursiveQuestionConfiguration()
    {
        Map(p => p.Requires("TP_QUESTION").HasValue("D"));
    }
}

public class VisualQuestionConfiguration : EntityTypeConfiguration<VisualQuestion>
{
    public VisualQuestionConfiguration()
    {
        Map(p => p.Requires("TP_QUESTION").HasValue("V"));
    }
}

public class ObjectiveQuestionConfiguration : EntityTypeConfiguration<ObjectiveQuestion>
{
    public ObjectiveQuestionConfiguration()
    {
        Map(p => p.Requires("TP_QUESTION").HasValue("O"));
    }
}

正在注册：

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Configurations.Add(new QuestionConfiguration());
    modelBuilder.Configurations.Add(new VisualQuestionConfiguration());
    modelBuilder.Configurations.Add(new ObjectiveQuestionConfiguration());
    modelBuilder.Configurations.Add(new DiscursiveQuestionConfiguration());
}

无法在 EF 6 上使用 Fluent API 创建 TPH

Unable to create a TPH using Fluent API on EF 6

c#

entity-framework

tph

ef-fluent-api