EF+Code First 数据关系隐射及迁移笔记一

1.一对一关系（one to one）

1.1DataAnnotations方式

实体：书本实体，版本信息实体，一本书只能有一个版本号，版本号在没有书出版的情况下是无意义的

 public class Book
 {
        /// <summary>
        /// Id,主键
        /// </summary>
        [Key]
        public int BookID { get; set; }

        /// <summary>
        /// 书籍名称
        /// </summary>
        public string Name { get; set; }

        /// <summary>
        /// 书籍类型
        /// </summary>
        public string Category { get; set; }

        /// <summary>
        /// 出版数量
        /// </summary>
        public int Numberofcopies { get; set; }

        /// <summary>
        /// 作者Id
        /// </summary>
        public int AuthorID { get; set; }

        /// <summary>
        /// 书籍价格
        /// </summary>
        public decimal Price { get; set; }

        /// <summary>
        /// 出版日期
        /// </summary>
        public DateTime PublishDate { get; set; }

        /// <summary>
        /// 评级
        /// </summary>
        public string Rating { get; set; }

        /// <summary>
        /// 版本号Id
        /// </summary>
        public int VersionId { get; set; }

        /// <summary>
        /// 一对一版本号信息
        /// </summary>
        public PublishInfo publish { get; set; }

        /// <summary>
        /// 作者信息
        /// </summary>
        public Author author { get; set; }
}

 public class PublishInfo
{
        /// <summary>
        /// 版本Id
        /// </summary>
        [Key]
        [ForeignKey("book")] 设置此字段为Book的外键
        public int VersionId { get; set; }

        /// <summary>
        /// 版本号
        /// </summary>
        public string VersionNum { get; set; }

        /// <summary>
        /// 出版社名称
        /// </summary>
        public string PressName { get; set; }

        /// <summary>
        /// 关联的书本信息
        /// </summary>
        public virtual Book book { get; set; }
}

　　说明：

[ForeignKey("book")] 为设置外键，设置了版本信息的主键为书本实体的外键，在使用DataAnnotations方式的时候，记得要引用“System.ComponentModel.DataAnnotations”和“System.ComponentModel.DataAnnotations.Schema”命名空间

1.2Fluent API方式
在以上实体的基础上添加两个映射类代码如下：

public PublishInfoMap()
{
            this.HasKey(p => p.VersionId);
            this.Property(p => p.VersionId).HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);
            this.Property(p => p.VersionNum).HasColumnType("nvarchar").HasMaxLength(50);
            this.Property(p => p.PressName).HasColumnType("nvarchar").HasMaxLength(100);
            this.ToTable(" PublishInfo");
            this.HasRequired(p => p.book).WithRequiredDependent(p => p.publish);
}

public BookMap()
 {
            this.HasKey(b => b.BookID).Property(b => b.BookID).HasColumnName("B_Id");
            this.Property(b => b.PublishDate).HasColumnType("datetime").IsRequired();
            this.Property(b => b.Price).HasColumnType("decimal").IsRequired();
            this.Property(b => b.Name).HasColumnType("nvarchar").HasMaxLength(200).IsRequired();
            this.Property(b => b.Rating).HasColumnType("nvarchar").HasMaxLength(5).IsRequired();
            this.Property(b => b.Category).HasColumnType("nvarchar").HasMaxLength(50).IsRequired();
            this.HasRequired(b => b.author).WithMany(b => b.books).HasForeignKey(b => b.AuthorID);
            this.ToTable("Book");
}

　说明：

this.HasRequired(p => p.book).WithRequiredDependent(p => p.publish);
此段代码设置了两张表的一对一映射关系
2.一对多关系（one to More）
实体：一本书只能有一个作者，一个作者可以有多本数

 public class Book
 {
        /// <summary>
        /// Id,主键
        /// </summary>
        public int BookID { get; set; }

        /// <summary>
        /// 书籍名称
        /// </summary>
        public string Name { get; set; }

        /// <summary>
        /// 书籍类型
        /// </summary>
        public string Category { get; set; }

        /// <summary>
        /// 出版数量
        /// </summary>
        public int Numberofcopies { get; set; }

        /// <summary>
        /// 作者Id
        /// </summary>
        public int AuthorID { get; set; }

        /// <summary>
        /// 书籍价格
        /// </summary>
        public decimal Price { get; set; }

        /// <summary>
        /// 出版日期
        /// </summary>
        public DateTime PublishDate { get; set; }

        /// <summary>
        /// 评级
        /// </summary>
        public string Rating { get; set; }

        /// <summary>
        /// 版本号Id
        /// </summary>
        public int VersionId { get; set; }

        /// <summary>
        /// 一对一版本号信息
        /// </summary>
        public PublishInfo publish { get; set; }

        /// <summary>
        /// 作者信息
        /// </summary>
        public Author author { get; set; }
}

 public class Author
    {
        /// <summary>
        /// 主键Id
        /// </summary>
        public int AuthorID { get; set; }

        /// <summary>
        /// 姓名
        /// </summary>
        public string Name { get; set; }

        /// <summary>
        /// 性别
        /// </summary>
        public int Sex { get; set; }

        /// <summary>
        /// 国籍
        /// </summary>
        public string Country { get; set; }

        public virtual ICollection<Book> books { get; set; }
    }

　2.1DataAnnotations方式　

[ForeignKey("AuthorID")]

public Author author { get; set; }
在book实体上设置以上代码
2.2Fluent Api方式

 public BookMap()
        {
            this.HasKey(b => b.BookID).Property(b => b.BookID).HasColumnName("B_Id");
            this.Property(b => b.PublishDate).HasColumnType("datetime").IsRequired();
            this.Property(b => b.Price).HasColumnType("decimal").IsRequired();
            this.Property(b => b.Name).HasColumnType("nvarchar").HasMaxLength(200).IsRequired();
            this.Property(b => b.Rating).HasColumnType("nvarchar").HasMaxLength(5).IsRequired();
            this.Property(b => b.Category).HasColumnType("nvarchar").HasMaxLength(50).IsRequired();
            this.HasRequired(b => b.author).WithMany(b => b.books).HasForeignKey(b => b.AuthorID);
            this.ToTable("Book");
        }

 public AuthorMap()
        {
            this.ToTable("Author");
            this.HasKey(a => a.AuthorID);
            this.Property(a => a.Name).HasColumnType("nvarchar").HasMaxLength(50);
            this.Property(a => a.Country).HasColumnType("nvarchar").HasMaxLength(30);
            this.HasMany(a => a.books).WithRequired(a => a.author).HasForeignKey(a => a.AuthorID);
        }

设置：

BookMap类和

AuthorMap类

this.HasRequired(b => b.author).WithMany(b => b.books).HasForeignKey(b => b.AuthorID);

this.HasMany(a => a.books).WithRequired(a => a.author).HasForeignKey(a => a.AuthorID);

数据迁移
启动迁移：Enable-Migrations;
添加迁移文件：Add-Migration Info(文件的名称)
迁移到数据库:Update-Database
说明：“在与 SQL Server 建立连接时出现与网络相关的或特定于实例的错误。未找到或无法访问服务器。
请验证实例名称是否正确并且 SQL Server 已配置为允许远程连接。 (provider: SQL Network Interfaces, error: 26 - 定位指定的服务器/实例时出错)”
若出现这个错误，需要指定要迁移的项目名称：Update-Database -StartUpProjectName "ContextConfig"（你要迁移的项目名称）