Entityframework 核心如何在不创建连接表的情况下映射多对多 [英] Entityframework core how to map Many-to-Many without creating a join table

问题描述

我正在尝试将此活动从现有的 .edmx 项目克隆到代码.

I am trying this activity to clone from existing .edmx project to code first.

我有两个实体.我想在不创建新表的情况下拥有多对多关系.我正在使用 EF Core 2.0 代码优先方法.

I have two entities. I want to have many to many relation without creating a new table. I am using EF Core 2.0 code first approach.

请在下面找到我创建的实体.我不确定这是否是正确的做法.

Please find below the entity i have created. I am not sure whether is this is the right way to do this.

我想在两个表上都有外键列，即.WorkCase 和 Workflow 表上的 WorkflowId 和 WorkCaseId.

I would like to have the foreign key column on both the tables ie. WorkflowId and WorkCaseId on WorkCase and Workflow tables respectively.

    public class WorkCase
    {
        [Key]
        public int WorkCaseId { get; set; }

        public int WorkflowId { get; set; }

        public int CaseDetailId {get;set;}

        public CaseDetail CaseDetail {get;set;}

        public WorkFlow WorkFlow { get; set; }

        public ICollection<WorkFlow> WorkFlows { get; set; }
    }

    public class WorkFlow : BaseEntity
    {
        [Key]
        public int WorkFlowId { get; set; }

        public string Comment { get; set; }

        public DateTime? UpdateDate { get; set; }

        public int WorkCaseId { get; set; }

        public WorkCase WorkCase { get; set; }

        public ICollection<WorkCase> WorkCases { get; set; }
    }

我的期望如下.任何人都可以帮助如何实现 EF Core 配置:- Workcase 将具有最新的工作流 ID- 工作流将具有每个工作案例 ID 的历史记录.

My expectation is as below. Can anyone help how to achieve the EF Core configuration: - Workcase will have the latest workflowid - workflow will have history for each workcaseid.

谢谢

推荐答案

UPDATE:EF5+ 支持多对多，无需显式映射连接表.请参阅 本EF公告正如对您的问题的评论，EF Core <= 2.2 尚不支持没有连接表的多对多关系.这是一个问题在 EF Core 存储库的backlock 中跟踪，并且可能会使其成为 3.0 版.

UPDATE: EF5+ supports many-to-many without explicitly mapping the join table. See this EF announcement As commented on your question, EF Core <= 2.2 does not yet support many-to-many relationships without a join table. This is an issue tracked in the EF Core repo's backlock, and will maybe make it into version 3.0.

在您的情况下，您需要引入一个与两个父表相关的新表.在这种情况下，您的模型将类似于以下内容:

In your case you'll need to introduce a new table that relates to both parent tables. In this case, your model will like something like the following:

public class WorkCase
{
    public int WorkCaseId { get; set; }

    public int CaseDetailId { get; set; }

    public CaseDetail CaseDetail { get; set; }

    public ICollection<WorkCaseWorkflow> Workflows { get; set; }
}

public class Workflow
{
    public int WorkflowId { get; set; }

    public string Comment { get; set; }

    public DateTime? UpdateDate { get; set; }

    public ICollection<WorkCaseWorkflow> WorkCases { get; set; }
}

public class WorkCaseWorkflow
{
    public int WorkCaseId { get; set; }
    public WorkCase WorkCase { get; set; }

    public int WorkflowId { get; set; }
    public Workflow Workflow { get; set; }
}

然后在您的 DbContext 子类中，覆盖 OnModelCreating 并添加以下代码:

Then in your DbContext subclass, override the OnModelCreating and add the following code:

protected override void OnModelCreating(ModelBuilder builder)
{
    var ww = builder.Entity<WorkCaseWorkflow>();
    ww.HasKey(w => new { w.WorkCaseId, WorkflowId });
    ww.HasOne(w => w.WorkCase)
      .WithMany(wc => wc.Workflows)
      .HasForeignKey(w => w.WorkCaseId);
    ww.HasOne(w => w.Workflow)
      .WithMany(wc => wc.WorkCases)
      .HasForeignKey(w => w.WorkflowId);
}

我不熟悉您的模型，但您可以将共享属性移动到连接表中.

I'm not familiar with your model, but you can move the shared properties to the join table.

但是，@Arthur Vickers(EF Core dev 成员)有一系列很棒的文章团队)关于如何缓解多对多关系:

However, there is a great series of articles by @Arthur Vickers (a member in the EF Core dev team) on how to easen up many-to-many relationships:

• 第 1 部分:基础知识
• 第 2 部分:隐藏为 IEnumerable
• 第 3 部分:隐藏为 ICollection
• 第 4 部分:更一般的抽象

这篇关于Entityframework 核心如何在不创建连接表的情况下映射多对多的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！