如何首先与实体框架代码创建多对多关系？答案

【问题标题】：How do I create a many-to-many relationship with Entity Framework code first?如何首先与实体框架代码创建多对多关系？
【发布时间】：2015-03-14 09:46:57
【问题描述】：

尝试创建代码优先多对多关系时显示以下错误。有人可以告诉我有什么问题吗？我到处搜索，看不出代码有什么问题。

在表“BookingPeople”上引入 FOREIGN KEY 约束“FK_dbo.BookingPeople_dbo.People_PersonID”可能会导致循环或多个级联路径。指定 ON DELETE NO ACTION 或 ON UPDATE NO ACTION，或修改其他 FOREIGN KEY 约束。无法创建约束或索引。查看以前的错误。

迁移：

        public override void Up()
    {
        CreateTable(
            "dbo.Bookings",
            c => new
                {
                    BookingID = c.Int(nullable: false),
                    startDate = c.DateTime(nullable: false),
                    endDate = c.DateTime(nullable: false),
                    Contact_PersonID = c.Int(nullable: false),
                    Type_BookingTypeID = c.Int(nullable: false),
                })
            .PrimaryKey(t => t.BookingID)
            .ForeignKey("dbo.People", t => t.Contact_PersonID, cascadeDelete: true)
            .ForeignKey("dbo.BookingTypes", t => t.Type_BookingTypeID, cascadeDelete: true)
            .Index(t => t.Contact_PersonID)
            .Index(t => t.Type_BookingTypeID);

        CreateTable(
            "dbo.People",
            c => new
                {
                    PersonID = c.Int(nullable: false),
                    PersonAge = c.Int(nullable: false),
                    Type_PersonTypeID = c.Int(nullable: false),
                })
            .PrimaryKey(t => t.PersonID)
            .ForeignKey("dbo.PersonTypes", t => t.Type_PersonTypeID, cascadeDelete: true)
            .Index(t => t.Type_PersonTypeID);

        CreateTable(
            "dbo.PersonTypes",
            c => new
                {
                    PersonTypeID = c.Int(nullable: false, identity: true),
                    Type = c.String(),
                })
            .PrimaryKey(t => t.PersonTypeID);

        CreateTable(
            "dbo.BookingTypes",
            c => new
                {
                    BookingTypeID = c.Int(nullable: false, identity: true),
                    Type = c.String(),
                })
            .PrimaryKey(t => t.BookingTypeID);

        CreateTable(
            "dbo.Users",
            c => new
                {
                    UserID = c.Int(nullable: false),
                    Username = c.String(maxLength: 30),
                    Password = c.String(unicode: false),
                })
            .PrimaryKey(t => t.UserID);

        CreateTable(
            "dbo.BookingPeople",
            c => new
                {
                    BookingID = c.Int(nullable: false),
                    PersonID = c.Int(nullable: false),
                })
            .PrimaryKey(t => new { t.BookingID, t.PersonID })
            .ForeignKey("dbo.Bookings", t => t.BookingID, cascadeDelete: true)
            .ForeignKey("dbo.People", t => t.PersonID, cascadeDelete: true)
            .Index(t => t.BookingID)
            .Index(t => t.PersonID);

    }

流畅的 API 代码：

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<User>()
            .Property(e => e.Password)
            .IsUnicode(false);

            modelBuilder.Entity<Booking>()
            .HasMany(t => t.People)
            .WithMany(t => t.Bookings)
            .Map(m =>
            {
                m.ToTable("BookingPeople");
                m.MapLeftKey("BookingID");
                m.MapRightKey("PersonID");
            });
    }

预订舱位：

    public class Booking
{
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public int BookingID { get; set; }

    [Required]
    public BookingType Type { get; set; }

    [Required]
    public Person Contact { get; set; }

    [Required]
    public DateTime startDate { get; set; }

    [Required]
    public DateTime endDate { get; set; }

    public virtual ICollection<Person> People { get; set; }

}

人物类：

    public class Person
{
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public int PersonID { get; set; }

    [Required]
    public int PersonAge { get; set; }

    [Required]
    public PersonType Type { get; set; }

    public virtual ICollection<Booking> Bookings { get; set; }
}

更新代码

迁移：

 public override void Up()
    {
        CreateTable(
            "dbo.Bookings",
            c => new
                {
                    BookingID = c.Int(nullable: false),
                    startDate = c.DateTime(nullable: false),
                    endDate = c.DateTime(nullable: false),
                    BookingType_BookingTypeID = c.Int(),
                })
            .PrimaryKey(t => t.BookingID)
            .ForeignKey("dbo.People", t => t.BookingID)
            .ForeignKey("dbo.BookingTypes", t => t.BookingType_BookingTypeID)
            .ForeignKey("dbo.BookingTypes", t => t.BookingID)
            .Index(t => t.BookingID)
            .Index(t => t.BookingType_BookingTypeID);

        CreateTable(
            "dbo.People",
            c => new
                {
                    PersonID = c.Int(nullable: false),
                    PersonAge = c.Int(nullable: false),
                    PersonType_PersonTypeID = c.Int(),
                })
            .PrimaryKey(t => t.PersonID)
            .ForeignKey("dbo.PersonTypes", t => t.PersonType_PersonTypeID)
            .ForeignKey("dbo.PersonTypes", t => t.PersonID)
            .Index(t => t.PersonID)
            .Index(t => t.PersonType_PersonTypeID);

        CreateTable(
            "dbo.PersonTypes",
            c => new
                {
                    PersonTypeID = c.Int(nullable: false, identity: true),
                    Type = c.String(),
                })
            .PrimaryKey(t => t.PersonTypeID);

        CreateTable(
            "dbo.BookingTypes",
            c => new
                {
                    BookingTypeID = c.Int(nullable: false, identity: true),
                    Type = c.String(),
                })
            .PrimaryKey(t => t.BookingTypeID);

        CreateTable(
            "dbo.Users",
            c => new
                {
                    UserID = c.Int(nullable: false, identity: true),
                    Username = c.String(maxLength: 30),
                    Password = c.String(unicode: false),
                })
            .PrimaryKey(t => t.UserID);

        CreateTable(
            "dbo.BookingPeople",
            c => new
                {
                    BookingID = c.Int(nullable: false),
                    PersonID = c.Int(nullable: false),
                })
            .PrimaryKey(t => new { t.BookingID, t.PersonID })
            .ForeignKey("dbo.Bookings", t => t.BookingID, cascadeDelete: true)
            .ForeignKey("dbo.People", t => t.PersonID, cascadeDelete: true)
            .Index(t => t.BookingID)
            .Index(t => t.PersonID);

    }

预订：

    public partial class Booking
{        
    public int BookingID { get; set; }


    public BookingType Type { get; set; }


    public Person Contact { get; set; }


    public DateTime startDate { get; set; }


    public DateTime endDate { get; set; }

    public virtual ICollection<Person> People { get; set; }

}

人：

    public partial class Person
{        
    public int PersonID { get; set; }

    public int PersonAge { get; set; }

    public PersonType Type { get; set; }

    public virtual ICollection<Booking> Bookings { get; set; }
}

流畅的 API 代码：

protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<User>()
            .Property(e => e.Password)
            .IsUnicode(false);

        // Booking
        // -------

        modelBuilder.Entity<Booking>()
        .HasRequired(b => b.Contact)
        .WithOptional()
        .WillCascadeOnDelete(false);

        modelBuilder.Entity<Booking>()
        .HasRequired(b => b.Type)
        .WithOptional()
        .WillCascadeOnDelete(false);

        modelBuilder.Entity<Booking>()
        .HasMany(t => t.People)
        .WithMany(t => t.Bookings)
        .Map(m =>
        {
            m.ToTable("BookingPeople");
            m.MapLeftKey("BookingID");
            m.MapRightKey("PersonID");
        });


        // Person
        // ------

        modelBuilder.Entity<Person>()
        .HasRequired(b => b.Type)
        .WithOptional()
        .WillCascadeOnDelete(false);


    }

更新代码：

迁移：

 public override void Up()
    {
        CreateTable(
            "dbo.Bookings",
            c => new
                {
                    BookingID = c.Int(nullable: false, identity: true),
                    startDate = c.DateTime(nullable: false),
                    endDate = c.DateTime(nullable: false),
                    Contact_PersonID = c.Int(nullable: false),
                    BookingType_BookingTypeID = c.Int(),
                    Type_BookingTypeID = c.Int(nullable: false),
                })
            .PrimaryKey(t => t.BookingID)
            .ForeignKey("dbo.People", t => t.Contact_PersonID)
            .ForeignKey("dbo.BookingTypes", t => t.BookingType_BookingTypeID)
            .ForeignKey("dbo.BookingTypes", t => t.Type_BookingTypeID)
            .Index(t => t.Contact_PersonID)
            .Index(t => t.BookingType_BookingTypeID)
            .Index(t => t.Type_BookingTypeID);

        CreateTable(
            "dbo.People",
            c => new
                {
                    PersonID = c.Int(nullable: false, identity: true),
                    PersonAge = c.Int(nullable: false),
                    PersonType_PersonTypeID = c.Int(),
                    Type_PersonTypeID = c.Int(nullable: false),
                })
            .PrimaryKey(t => t.PersonID)
            .ForeignKey("dbo.PersonTypes", t => t.PersonType_PersonTypeID)
            .ForeignKey("dbo.PersonTypes", t => t.Type_PersonTypeID)
            .Index(t => t.PersonType_PersonTypeID)
            .Index(t => t.Type_PersonTypeID);

        CreateTable(
            "dbo.PersonTypes",
            c => new
                {
                    PersonTypeID = c.Int(nullable: false, identity: true),
                    Type = c.String(),
                })
            .PrimaryKey(t => t.PersonTypeID);

        CreateTable(
            "dbo.BookingTypes",
            c => new
                {
                    BookingTypeID = c.Int(nullable: false, identity: true),
                    Type = c.String(),
                })
            .PrimaryKey(t => t.BookingTypeID);

        CreateTable(
            "dbo.Users",
            c => new
                {
                    UserID = c.Int(nullable: false, identity: true),
                    Username = c.String(maxLength: 30),
                    Password = c.String(unicode: false),
                })
            .PrimaryKey(t => t.UserID);

        CreateTable(
            "dbo.BookingPeople",
            c => new
                {
                    BookingID = c.Int(nullable: false),
                    PersonID = c.Int(nullable: false),
                })
            .PrimaryKey(t => new { t.BookingID, t.PersonID })
            .ForeignKey("dbo.Bookings", t => t.BookingID, cascadeDelete: true)
            .ForeignKey("dbo.People", t => t.PersonID, cascadeDelete: true)
            .Index(t => t.BookingID)
            .Index(t => t.PersonID);

    }

流畅的 API 代码：

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<User>()
            .Property(e => e.Password)
            .IsUnicode(false);

        // Booking
        // -------

        modelBuilder.Entity<Booking>()
        .HasRequired(b => b.Contact)
        .WithMany()
        .WillCascadeOnDelete(false);

         modelBuilder.Entity<Booking>()
        .HasRequired(b => b.Type)
        .WithMany()
        .WillCascadeOnDelete(false);

        modelBuilder.Entity<Booking>()
        .HasMany(t => t.People)
        .WithMany(t => t.Bookings)
        .Map(m =>
        {
            m.ToTable("BookingPeople");
            m.MapLeftKey("BookingID");
            m.MapRightKey("PersonID");
        });


        // Person
        // ------

        modelBuilder.Entity<Person>()
        .HasRequired(b => b.Type)
        .WithMany()
        .WillCascadeOnDelete(false);


    }

【问题讨论】：

标签： c# entity-framework

【解决方案1】：

我认为这可能是问题

[Required]
public Person Contact { get; set; }

Required 属性意味着 EF 将级联删除设置为 true（例如，当您删除预订时，联系人（人员）被删除，但该人可能被另一个预订引用，因此出现错误消息

修复删除所需属性并在FluentApi中指定关系

在您的 DbContext 类中

modelBuilder.Entity<Booking>()
            .HasRequired(b => b.Contact)
            .WithOptional()
            .WillCascadeOnDelete(false);

【讨论】：

我已经添加了代码，但现在 Contact 不是迁移的一部分。我已将最新代码上传到帖子中。
.WithOptional() 应该是WithMany()。 @JamesPeters我认为这个答案是正确的。现在Booking 中应该有一个指向Person 的外键。
我已经添加了 WithMany()，现在在上述迁移中，Person in Booking 有一个外键，但现在有一个额外的外键和 BookingType 字段，但不存在。