c# - EF Core 2.1 - 如何映射具有相同类型的多对多

Question

我有一个非常具体的问题，我想在这里寻求帮助。 我将 .NET Core 2.1.1 与 EF Core 2.1.1 结合使用。我正在使用代码优先方法，目前正在为我的应用程序设计域模型。

所以我有以下要求:我有一个 TrainingItem 类，其中包含有关训练的基本信息。 TrainingItem 还包含参与者列表，因此我在 TrainingItem 和 TrainingEmployee 之间使用多对多关系。问题是我要求 TrainingItem 应包含正在等待此培训的员工列表，因此我想出了以下方法:

public class TrainingItem 
{
  // ... properties for Training
  public virtual ICollection<TrainingEmployeeTrainingItem> Attendees {get;set;} = new List<TrainingEmployeeTrainingItem>();

  public virtual ICollection<TrainingEmployeeTrainingItem> WaitingList {get;set;} = new List<TrainingEmployeeTrainingItem>();  
}

public class TrainingEmployee
{
    // ... properties for Employee
    public virtual ICollection<TrainingEmployeeTrainingItem> TrainingEmployeeTrainingItems {get;set;} = new List<TrainingEmployeeTrainingItem>();
}

public class TrainingEmployeeTrainingItem
{
    public int TrainingEmployeeId {get;set;}
    public virtual TrainingEmployee TrainingEmployee {get;set;}

    public int TrainingItemId {get;set;}
    public virtual TrainingItem TrainingItem {get;set;}
}

// this is my model creating method in db context
protected override void OnModelCreating(ModelBuilder builder)
{
    // many-to-many
    builder.Entity<TrainingEmployeeTrainingItem>()
        .HasKey(x => new { x.TrainingEmployeeId, x.TrainingItemId });
}

正如您所看到的，可以使用 EF Core 中当前用于映射多对多关系的解决方法来映射第一个与会者列表。

但问题是，如何映射 WaitingList？

Answer 1

每个多对多都需要一个额外的实体，因此仅 TrainingEmployeeTrainingItem 不行。

尝试以下操作:

public class TrainingItem 
{
  // ... properties for Training
  public virtual ICollection<AttendeeTrainingEmployeeTrainingItem> Attendees {get;set;} = new List<AttendeeTrainingEmployeeTrainingItem>();

  public virtual ICollection<WaitingListTrainingEmployeeTrainingItem> WaitingList {get;set;} = new List<WaitingListTrainingEmployeeTrainingItem>();  
}

public class TrainingEmployee
{
    // ... properties for Employee
    public virtual ICollection<AttendeeTrainingEmployeeTrainingItem> AttendingTrainings {get;set;} = new List<AttendeeTrainingEmployeeTrainingItem>();
    public virtual ICollection<WaitingListTrainingEmployeeTrainingItem> AwaitingTrainings {get;set;} = new List<WaitingListTrainingEmployeeTrainingItem>();
}

public abstract class TrainingEmployeeTrainingItem
{
    public int TrainingEmployeeId {get;set;}
    public virtual TrainingEmployee TrainingEmployee {get;set;}

    public int TrainingItemId {get;set;}
    public virtual TrainingItem TrainingItem {get;set;}
}

public class AttendeeTrainingEmployeeTrainingItem : TrainingEmployeeTrainingItem
{
}

public class WaitingListTrainingEmployeeTrainingItem : TrainingEmployeeTrainingItem
{
}

// this is my model creating method in db context
protected override void OnModelCreating(ModelBuilder builder)
{
    // many-to-many
    builder.Entity<AttendeeTrainingEmployeeTrainingItem>()
        .HasKey(x => new { x.TrainingEmployeeId, x.TrainingItemId });
    builder.Entity<WaitingListTrainingEmployeeTrainingItem>()
        .HasKey(x => new { x.TrainingEmployeeId, x.TrainingItemId });
}