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.NET 云原生架构师训练营(模块二 基础巩固 EF Core 关系)--学习笔记

2020-12-29 23:34 1131 查看

2.4.4 EF Core -- 关系

  • 一对多
  • 一对一
  • 多对多
  • 示例

关系:https://docs.microsoft.com/zh-cn/ef/core/modeling/relationships?tabs=fluent-api%2Cfluent-api-simple-key%2Csimple-key

一对多

// Dependent Entity 主表
public class Blog
{
// Principal Key 标识键/可能是主键或者备用键(唯一性约束)
public int BlogId { get; set; }

public string Url { get; set; }

// Collection navigation property 关联多个从表的属性集合(集合属性)
public List<Post> Posts { get; set; }
}

// Principal Entity 从表
public class Post
{
public int PostId { get; set; }

public string Title { get; set; }

public string Content { get; set; }

// Foreign Key 外键(指向主表中的 Principal Key)
// Inverse navigation property 反向导航属性
public int BlogId { get; set; }

// Inverse navigation property 反向导航属性
public Blog Blog { get; set; }
}

一对一

// Principal Entity 从表
public class Blog
{
public int BlogId { get; set; }

public string Url { get; set; }

public List<Post> Posts { get; set; }
}

// Dependent Entity 主表
public class Post
{
public int PostId { get; set; }

public string Title { get; set; }

public string Content { get; set; }

// Reference navigation property 一对一时指向另外一张表(引用属性)
public Blog Blog { get; set; }
}

多对多

public class Post
{
public int PostId { get; set; }

public string Title { get; set; }

public string Content { get; set; }

public ICollection<Tag> Tags { get; set; }
}

public class Tag
{
public string TagId { get; set; }

public ICollection<Post> Posts { get; set; }
}

示例

一对多

一个 Project 对应多个 ProjectGroup

在 Project 实体中添加 ProjectGroup 列表

public List<ProjectGroup> Groups { get; set; }

迁移

dotnet ef migrations add ProjectGroupCollectionProperty

生成集合属性 ProjectGroupCollectionProperty

protected override void Up(MigrationBuilder migrationBuilder)
{
migrationBuilder.AlterColumn<string>(
name: "ProjectId",
table: "ProjectGroups",
nullable: true,
oldClrType: typeof(string),
oldType: "longtext CHARACTER SET utf8mb4",
oldNullable: true);

migrationBuilder.CreateIndex(
name: "IX_ProjectGroups_ProjectId",
table: "ProjectGroups",
column: "ProjectId");

migrationBuilder.AddForeignKey(
name: "FK_ProjectGroups_Projects_ProjectId",
table: "ProjectGroups",
column: "ProjectId",
principalTable: "Projects",
principalColumn: "Id",
onDelete: ReferentialAction.Restrict);
}

手动配置

class MyContext : DbContext
{
public DbSet<Blog> Blogs { get; set; }

56c
public DbSet<Post> Posts { get; set; }

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
// 先在从表上建立一对一的关系,再从主表上建立一对多的关系
modelBuilder.Entity<Post>()
.HasOne(p => p.Blog)
.WithMany(b => b.Posts);
}
}

public class Blog
{
public int BlogId { get; set; }
public string Url { get; set; }

public List<Post> Posts { get; set; }
}

public class Post
{
public int PostId { get; set; }
public string Title { get; set; }
public string Content { get; set; }

public Blog Blog { get; set; }
}

LighterDbContext

// 一对一
modelBuilder.Entity<Project.ProjectGroup>().HasOne<Project.Project>(g => g.Project);
// 一对多
modelBuilder.Entity<Project.ProjectGroup>().HasOne<Project.Project>(g => g.Project).WithMany(p => p.Groups);

多对多

为 Project 和 Subject 建立中间表 SubjectProject

public class Project : Entity
{
public string Title { get; set; }

public DateTime StartDate { get; set; }

public DateTime EndDate { get; set; }

public
1cea
string SupervisorId { get; set; }

public string PlanId { get; set; }

public List<ProjectGroup> Groups { get; set; }
public List<SubjectProject> SubjectProjects { get; set; }
}

public class Subject : Entity
{
public string Title { get; set; }

public string Content { get; set; }

public List<SubjectProject> SubjectProjects { get; set; }
}

public class SubjectProject : Entity
{
public string ProjcetId { get; set; }

public Project Project { get; set; }

public string SubjectId { get; set; }

public Subject Subject { get; set; }
}

配置多对多关系

LighterDbContext

// 多对多(两组一对多)
modelBuilder.Entity<Project.SubjectProject>()
.HasOne<Project.Project>(s => s.Project)
.WithMany(p => p.SubjectProjects)
.HasForeignKey(s => s.ProjcetId);

modelBuilder.Entity<Project.SubjectProject>()
.HasOne<Project.Subject>(s => s.Subject)
.WithMany(p => p.SubjectProjects)
.HasForeignKey(s => s.SubjectId);

迁移

dotnet ef migrations add SubjectProjectManyToManyRelation

SubjectProjectManyToManyRelation

table.ForeignKey(
name: "FK_SubjectProject_Projects_ProjcetId",
column: x => x.ProjcetId,
principalTable: "Projects",
principalColumn: "Id",
onDelete: ReferentialAction.Restrict);
table.ForeignKey(
name: "FK_SubjectProject_Subject_SubjectId",
column: x => x.SubjectId,
principalTable: "Subject",
principalColumn: "Id",
onDelete: ReferentialAction.Restrict);

中间表创建了两个外键,形成多对多

EF Core 5.0 多对多实现

public class Post
{
public int PostId { get; set; }
public string Title { get; set; }
public string Content { get; set; }

public ICollection<Tag> Tags { get; set; }
}

public class Tag
{
public string TagId { get; set; }

public ICollection<Post> Posts { get; set; }
}

迁移的时候会自动生成中间表

联接实体类型配置 HasMany

modelBuilder
.Entity<Post>()
.HasMany(p => p.Tags)
.WithMany(p => p.Posts)
.UsingEntity(j => j.ToTable("PostTags"));

GitHub源码链接:

https://github.com/MINGSON666/Personal-Learning-Library/tree/main/ArchitectTrainingCamp/LighterApi

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