使用关联表中的其他字段首先创建代码，多对多创建代码

时间：2011-08-13 12:29:22

标签： c# entity-framework ef-code-first many-to-many

我有这种情况：

public class Member
{
    public int MemberID { get; set; }

    public string FirstName { get; set; }
    public string LastName { get; set; }

    public virtual ICollection<Comment> Comments { get; set; }
}

public class Comment
{
    public int CommentID { get; set; }
    public string Message { get; set; }

    public virtual ICollection<Member> Members { get; set; }
}

public class MemberComment
{
    public int MemberID { get; set; }
    public int CommentID { get; set; }
    public int Something { get; set; }
    public string SomethingElse { get; set; }
}

如何配置与fluent API的关联？或者有更好的方法来创建关联表吗？

6 个答案:

答案 0 :(得分：497)

无法与自定义连接表创建多对多关系。在多对多关系中，EF在内部管理连接表并隐藏。它是一个没有模型中的Entity类的表。要使用具有其他属性的此类连接表，您必须实际创建两个一对多关系。它看起来像这样：

public class Member
{
    public int MemberID { get; set; }

    public string FirstName { get; set; }
    public string LastName { get; set; }

    public virtual ICollection<MemberComment> MemberComments { get; set; }
}

public class Comment
{
    public int CommentID { get; set; }
    public string Message { get; set; }

    public virtual ICollection<MemberComment> MemberComments { get; set; }
}

public class MemberComment
{
    [Key, Column(Order = 0)]
    public int MemberID { get; set; }
    [Key, Column(Order = 1)]
    public int CommentID { get; set; }

    public virtual Member Member { get; set; }
    public virtual Comment Comment { get; set; }

    public int Something { get; set; }
    public string SomethingElse { get; set; }
}

如果您现在想要查找LastName =“Smith”成员的所有评论，例如您可以编写如下查询：

var commentsOfMembers = context.Members
    .Where(m => m.LastName == "Smith")
    .SelectMany(m => m.MemberComments.Select(mc => mc.Comment))
    .ToList();

......或...... 

var commentsOfMembers = context.MemberComments
    .Where(mc => mc.Member.LastName == "Smith")
    .Select(mc => mc.Comment)
    .ToList();

或者要创建一个名为“Smith”的成员列表（我们假设有多个）以及他们的评论，您可以使用投影：

var membersWithComments = context.Members
    .Where(m => m.LastName == "Smith")
    .Select(m => new
    {
        Member = m,
        Comments = m.MemberComments.Select(mc => mc.Comment)
    })
    .ToList();

如果您想查找MemberId = 1的成员的所有评论：

var commentsOfMember = context.MemberComments
    .Where(mc => mc.MemberId == 1)
    .Select(mc => mc.Comment)
    .ToList();

现在，您还可以按联接表中的属性进行过滤（这在多对多关系中是不可能的），例如：过滤属性为{{1}的成员1的所有注释}：

Something

由于延迟加载，事情可能会变得更容易。如果您已加载var filteredCommentsOfMember = context.MemberComments .Where(mc => mc.MemberId == 1 && mc.Something == 99) .Select(mc => mc.Comment) .ToList(); ，则应该能够在没有明确查询的情况下获取注释：

Member

我想延迟加载会在幕后自动获取评论。

修改

只是为了好玩一些例子，更多如何添加实体和关系以及如何在此模型中删除它们：

1）创建该成员的一个成员和两个评论：

var commentsOfMember = member.MemberComments.Select(mc => mc.Comment);

2）添加member1的第三条评论：

var member1 = new Member { FirstName = "Pete" };
var comment1 = new Comment { Message = "Good morning!" };
var comment2 = new Comment { Message = "Good evening!" };
var memberComment1 = new MemberComment { Member = member1, Comment = comment1,
                                         Something = 101 };
var memberComment2 = new MemberComment { Member = member1, Comment = comment2,
                                         Something = 102 };

context.MemberComments.Add(memberComment1); // will also add member1 and comment1
context.MemberComments.Add(memberComment2); // will also add comment2

context.SaveChanges();

3）创建新成员并将其与现有的comment2相关联：

var member1 = context.Members.Where(m => m.FirstName == "Pete")
    .SingleOrDefault();
if (member1 != null)
{
    var comment3 = new Comment { Message = "Good night!" };
    var memberComment3 = new MemberComment { Member = member1,
                                             Comment = comment3,
                                             Something = 103 };

    context.MemberComments.Add(memberComment3); // will also add comment3
    context.SaveChanges();
}

4）在现有成员2和评论3之间建立关系：

var comment2 = context.Comments.Where(c => c.Message == "Good evening!")
    .SingleOrDefault();
if (comment2 != null)
{
    var member2 = new Member { FirstName = "Paul" };
    var memberComment4 = new MemberComment { Member = member2,
                                             Comment = comment2,
                                             Something = 201 };

    context.MemberComments.Add(memberComment4);
    context.SaveChanges();
}

5）再次删除此关系：

var member2 = context.Members.Where(m => m.FirstName == "Paul")
    .SingleOrDefault();
var comment3 = context.Comments.Where(c => c.Message == "Good night!")
    .SingleOrDefault();
if (member2 != null && comment3 != null)
{
    var memberComment5 = new MemberComment { Member = member2,
                                             Comment = comment3,
                                             Something = 202 };

    context.MemberComments.Add(memberComment5);
    context.SaveChanges();
}

6）删除member1及其与评论的所有关系：

var memberComment5 = context.MemberComments
    .Where(mc => mc.Member.FirstName == "Paul"
        && mc.Comment.Message == "Good night!")
    .SingleOrDefault();
if (memberComment5 != null)
{
    context.MemberComments.Remove(memberComment5);
    context.SaveChanges();
}

这也会删除var member1 = context.Members.Where(m => m.FirstName == "Pete") .SingleOrDefault(); if (member1 != null) { context.Members.Remove(member1); context.SaveChanges(); } 中的关系，因为MemberComments和Member之间以及MemberComments和Comment之间的一对多关系已设置为按惯例级联删除。情况就是如此，因为MemberComments中的MemberId和CommentId被检测为MemberComment和Member导航属性的外键属性，因为FK属性是类型为非可空Comment的关系是必需的，最终导致级联删除设置。我认为这个模型很有意义。

答案 1 :(得分：93)

Slauma的

优秀的回答。

我将使用流畅的API映射发布代码来执行此操作。 

public class User {
    public int UserID { get; set; }
    public string Username { get; set; }
    public string Password { get; set; }

    public ICollection<UserEmail> UserEmails { get; set; }
}

public class Email {
    public int EmailID { get; set; }
    public string Address { get; set; }

    public ICollection<UserEmail> UserEmails { get; set; }
}

public class UserEmail {
    public int UserID { get; set; }
    public int EmailID { get; set; }
    public bool IsPrimary { get; set; }
}

在DbContext派生类中，您可以这样做：

public class MyContext : DbContext {
    protected override void OnModelCreating(DbModelBuilder builder) {
        // Primary keys
        builder.Entity<User>().HasKey(q => q.UserID);
        builder.Entity<Email>().HasKey(q => q.EmailID);
        builder.Entity<UserEmail>().HasKey(q => 
            new { 
                q.UserID, q.EmailID
            });

        // Relationships
        builder.Entity<UserEmail>()
            .HasRequired(t => t.Email)
            .WithMany(t => t.UserEmails)
            .HasForeignKey(t => t.EmailID)

        builder.Entity<UserEmail>()
            .HasRequired(t => t.User)
            .WithMany(t => t.UserEmails)
            .HasForeignKey(t => t.UserID)
    }
}

它与接受的答案具有相同的效果，采用不同的方法，不更好或更差。

编辑： 我已将CreatedDate从bool更改为DateTime。

编辑2： 由于时间不够，我从我正在研究的应用程序中找到了一个例子，以确保它有效。

答案 2 :(得分：10)

@Esteban，你提供的代码是对的，谢谢，但不完整，我已经测试过了。 “UserEmail”类中缺少属性：

    public UserTest UserTest { get; set; }
    public EmailTest EmailTest { get; set; }

如果有人感兴趣，我会发布我测试过的代码。 此致

using System.Data.Entity;
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using System.Linq;
using System.Web;

#region example2
public class UserTest
{
    public int UserTestID { get; set; }
    public string UserTestname { get; set; }
    public string Password { get; set; }

    public ICollection<UserTestEmailTest> UserTestEmailTests { get; set; }

    public static void DoSomeTest(ApplicationDbContext context)
    {

        for (int i = 0; i < 5; i++)
        {
            var user = context.UserTest.Add(new UserTest() { UserTestname = "Test" + i });
            var address = context.EmailTest.Add(new EmailTest() { Address = "address@" + i });
        }
        context.SaveChanges();

        foreach (var user in context.UserTest.Include(t => t.UserTestEmailTests))
        {
            foreach (var address in context.EmailTest)
            {
                user.UserTestEmailTests.Add(new UserTestEmailTest() { UserTest = user, EmailTest = address, n1 = user.UserTestID, n2 = address.EmailTestID });
            }
        }
        context.SaveChanges();
    }
}

public class EmailTest
{
    public int EmailTestID { get; set; }
    public string Address { get; set; }

    public ICollection<UserTestEmailTest> UserTestEmailTests { get; set; }
}

public class UserTestEmailTest
{
    public int UserTestID { get; set; }
    public UserTest UserTest { get; set; }
    public int EmailTestID { get; set; }
    public EmailTest EmailTest { get; set; }
    public int n1 { get; set; }
    public int n2 { get; set; }


    //Call this code from ApplicationDbContext.ConfigureMapping
    //and add this lines as well:
    //public System.Data.Entity.DbSet<yournamespace.UserTest> UserTest { get; set; }
    //public System.Data.Entity.DbSet<yournamespace.EmailTest> EmailTest { get; set; }
    internal static void RelateFluent(System.Data.Entity.DbModelBuilder builder)
    {
        // Primary keys
        builder.Entity<UserTest>().HasKey(q => q.UserTestID);
        builder.Entity<EmailTest>().HasKey(q => q.EmailTestID);

        builder.Entity<UserTestEmailTest>().HasKey(q =>
            new
            {
                q.UserTestID,
                q.EmailTestID
            });

        // Relationships
        builder.Entity<UserTestEmailTest>()
            .HasRequired(t => t.EmailTest)
            .WithMany(t => t.UserTestEmailTests)
            .HasForeignKey(t => t.EmailTestID);

        builder.Entity<UserTestEmailTest>()
            .HasRequired(t => t.UserTest)
            .WithMany(t => t.UserTestEmailTests)
            .HasForeignKey(t => t.UserTestID);
    }
}
#endregion

答案 3 :(得分：0)

<强> TLDR; （与EF6 / VS2012U5中的EF编辑器错误半关联）如果从DB生成模型并且您无法看到属性m：m表：删除两个相关表 - ＆gt;保存.edmx - ＆gt;从数据库生成/添加 - ＆gt;保存。

对于那些来到这里的人想知道如何获得与EF .edmx文件中显示的属性列的多对多关系（因为它当前不会显示并被视为一组导航属性），并且您从数据库表中生成这些类（或者我相信，在MS术语中是数据库优先的。）

在.edmx中删除有问题的2个表（以获取OP示例，成员和注释），然后通过“从数据库生成模型”再次添加它们。 （即不要试图让Visual Studio更新它们 - 删除，保存，添加，保存）

然后它将创建一个符合此处建议的第3个表。

这在首先添加纯多对多关系的情况下是相关的，并且稍后在DB中设计属性。

这个帖子/谷歌搜索没有立即清楚。所以只是把它放在那里，因为这是谷歌上的链接＃1寻找问题，但首先来自数据库方面。

答案 4 :(得分：0)

解决此错误的一种方法是将ForeignKey属性放在所需属性的顶部作为外键并添加导航属性。

注意：在ForeignKey属性中，在括号和双引号之间，以这种方式放置引用的类的名称。

enter image description here

答案 5 :(得分：0)

我想提出一个解决方案，可以实现多对多配置的两种风格。

“catch”是我们需要创建一个以Join Table为目标的视图，因为EF验证每个EntitySet最多可以映射一次模式表。

这个答案增加了以前答案中已经说过的内容，并没有覆盖任何这些方法，它建立在它们之上。

模特：

public class Member
{
    public int MemberID { get; set; }

    public string FirstName { get; set; }
    public string LastName { get; set; }

    public virtual ICollection<Comment> Comments { get; set; }
    public virtual ICollection<MemberCommentView> MemberComments { get; set; }
}

public class Comment
{
    public int CommentID { get; set; }
    public string Message { get; set; }

    public virtual ICollection<Member> Members { get; set; }
    public virtual ICollection<MemberCommentView> MemberComments { get; set; }
}

public class MemberCommentView
{
    public int MemberID { get; set; }
    public int CommentID { get; set; }
    public int Something { get; set; }
    public string SomethingElse { get; set; }

    public virtual Member Member { get; set; }
    public virtual Comment Comment { get; set; }
}

配置：

using System.ComponentModel.DataAnnotations.Schema;
using System.Data.Entity.ModelConfiguration;

public class MemberConfiguration : EntityTypeConfiguration<Member>
{
    public MemberConfiguration()
    {
        HasKey(x => x.MemberID);

        Property(x => x.MemberID).HasColumnType("int").IsRequired();
        Property(x => x.FirstName).HasColumnType("varchar(512)");
        Property(x => x.LastName).HasColumnType("varchar(512)")

        // configure many-to-many through internal EF EntitySet
        HasMany(s => s.Comments)
            .WithMany(c => c.Members)
            .Map(cs =>
            {
                cs.ToTable("MemberComment");
                cs.MapLeftKey("MemberID");
                cs.MapRightKey("CommentID");
            });
    }
}

public class CommentConfiguration : EntityTypeConfiguration<Comment>
{
    public CommentConfiguration()
    {
        HasKey(x => x.CommentID);

        Property(x => x.CommentID).HasColumnType("int").IsRequired();
        Property(x => x.Message).HasColumnType("varchar(max)");
    }
}

public class MemberCommentViewConfiguration : EntityTypeConfiguration<MemberCommentView>
{
    public MemberCommentViewConfiguration()
    {
        ToTable("MemberCommentView");
        HasKey(x => new { x.MemberID, x.CommentID });

        Property(x => x.MemberID).HasColumnType("int").IsRequired();
        Property(x => x.CommentID).HasColumnType("int").IsRequired();
        Property(x => x.Something).HasColumnType("int");
        Property(x => x.SomethingElse).HasColumnType("varchar(max)");

        // configure one-to-many targeting the Join Table view
        // making all of its properties available
        HasRequired(a => a.Member).WithMany(b => b.MemberComments);
        HasRequired(a => a.Comment).WithMany(b => b.MemberComments);
    }
}

背景信息：

using System.Data.Entity;

public class MyContext : DbContext
{
    public DbSet<Member> Members { get; set; }
    public DbSet<Comment> Comments { get; set; }
    public DbSet<MemberCommentView> MemberComments { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);

        modelBuilder.Configurations.Add(new MemberConfiguration());
        modelBuilder.Configurations.Add(new CommentConfiguration());
        modelBuilder.Configurations.Add(new MemberCommentViewConfiguration());

        OnModelCreatingPartial(modelBuilder);
     }
}

来自Saluma（@Saluma）answer

  

如果您现在想要查找具有LastName =的成员的所有评论   以“史密斯”为例，您可以编写如下查询：

这仍然有效...... 

var commentsOfMembers = context.Members
    .Where(m => m.LastName == "Smith")
    .SelectMany(m => m.MemberComments.Select(mc => mc.Comment))
    .ToList();

......但现在也可以...... 

var commentsOfMembers = context.Members
    .Where(m => m.LastName == "Smith")
    .SelectMany(m => m.Comments)
    .ToList();
  

或者创建一个名为“Smith”的成员列表（我们假设有   不止一个）以及他们的评论你可以使用投影：

这仍然有效...... 

var membersWithComments = context.Members
    .Where(m => m.LastName == "Smith")
    .Select(m => new
    {
        Member = m,
        Comments = m.MemberComments.Select(mc => mc.Comment)
    })
    .ToList();

......但现在也可以...... 

var membersWithComments = context.Members
    .Where(m => m.LastName == "Smith")
    .Select(m => new
    {
        Member = m,
        m.Comments
    })
        .ToList();

如果您要删除会员的评论

var comment = ... // assume comment from member John Smith
var member = ... // assume member John Smith

member.Comments.Remove(comment);

如果您想Include()成员的评论

var member = context.Members
    .Where(m => m.FirstName == "John", m.LastName == "Smith")
    .Include(m => m.Comments);

这一切都像语法糖，但如果你愿意通过额外的配置，它确实会给你一些好处。无论哪种方式，您似乎都能够充分利用这两种方法。

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