002 Entity Framework Core 2.x P2 表关系一对多多对多

EntityFrameworkCoreASP.NET Core

博客园文章Id:12700088

项目结构

AspEFCore.Data
AspEFCore.Domain.Models
AspEFCore.Web

AspEFCore.Data

需要引用的依赖项如下:

Microsoft.EntityFramework.Core.Tools

Microsoft.EntityFramework.Core.Design

编写EF上下文类:

using AspEFCore.DoMain.Models;
using Microsoft.EntityFrameworkCore;

namespace AspEFCore.Data
{
    public class MyContext : DbContext
    {
        /*
         * Ef Core 需要 DbContextOptions 类型的配置才能进行工作,所以此处的配置,我们需要在Startup类中进行注入,
         * 才能使用此DbContext.
         */
        public MyContext(DbContextOptions<MyContext> options) : base(options)
        {

        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<City>()
                .HasOne(x => x.Province)   //指向外键表的导航属性
                .WithMany(x => x.Cities)   //外键表的导航属性指向自己
                .HasForeignKey(x=>x.ProvinceId);             //外键表Id

            modelBuilder.Entity<CityCompany>()
                .HasKey(x => new {x.CityId, x.CompanyId});         //创建联合主键

            modelBuilder.Entity<CityCompany>()               
                .HasOne(x => x.City)             //指向外键表的导航属性
                .WithMany(x => x.CityCompanies)  //外键表的导航属性指向自己
                .HasForeignKey(x => x.CityId);                     //外键表Id

            modelBuilder.Entity<CityCompany>()
                .HasOne(x => x.Company)         //指向外键表的导航属性
                .WithMany(x => x.CityCompanies) //外键表的导航属性指向自己
                .HasForeignKey(x => x.CompanyId);                 //外键表Id

            modelBuilder.Entity<Mayor>()
                .HasOne(x => x.City)             //指向外键表的导航属性
                .WithOne(x=>x.Mayor)             //外键表的导航属性指向自己
                .HasForeignKey<Mayor>(x => x.CityId);             //外键表Id

        }

        public DbSet<Province> Province { get; set; }
        public DbSet<City> City { get; set; }
        public DbSet<CityCompany> CityCompany { get; set; }
        public DbSet<Mayor> Mayor { get; set; }
        public DbSet<Company> Company { get; set; }

    }
}

在此项目

AspEFCore.Domain.Models

需要引用的依赖项如下:

Microsoft.EntityFramework.Core
Microsoft.EntityFramework.SqlServer

编写相关表实体类:

City表

using System.Collections.Generic;

namespace AspEFCore.DoMain.Models
{
    public class City
    {
        /// <summary>
        /// 主键Id
        /// </summary>
        public int CityId { get; set; }

        /// <summary>
        /// 外键Id
        /// </summary>
        public int ProvinceId { get; set; }

        /// <summary>
        /// 导航属性
        /// </summary>
        public Province Province { get; set; }

        public IEnumerable<CityCompany> CityCompanies { get; set; }
        public Mayor Mayor { get; set; }
    }
}

Province表

using System.Collections.Generic;

namespace AspEFCore.DoMain.Models
{
    public class Province
    {
        public int ProvinceId { get; set; }
        public IEnumerable<City> Cities { get; set; }
    }
}

Company表

using System.Collections.Generic;

namespace AspEFCore.DoMain.Models
{
    public class Company
    {
        public int CompanyId { get; set; }
        public IEnumerable<CityCompany> CityCompanies { get; set; }
    }
}

CityCompany表

namespace AspEFCore.DoMain.Models
{
    public class CityCompany
    {
       public int CityCompanyId { get; set; }

        public int CityId { get; set; }
        public City City { get; set; }

        public int CompanyId { get; set; }
        public Company Company { get; set; }
    }
}

Mayor表

namespace AspEFCore.DoMain.Models
{
    public class Mayor
    {
        public int MayOrId { get; set; }

        public int CityId { get; set; }
        public City City { get; set; }
    }
}

AspEFCore.Web

需要引用的依赖项如下:

Microsoft.EntityFramework.Core.Tools

Microsoft.EntityFramework.Core.Design

需要引用的项目如下:

AspEFCore.Domain.Models
AspEFCore.Data

在appsettings.json文件中进行连接字符串的配置,配置如下:

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Warning",
      "Microsoft.Hosting.Lifetime": "Information"
    }
  },
  "AllowedHosts": "*",
  "ConnectionStrings": {
    "DefaultConnectionString": "Server =(localdb)\\MSSQLLocalDB;Database=AspEFCoreDemo; Trusted_Connection=True"
  }
}

在Startup.cs类的ConfigureServices方法进行连接字符串配置,配置如下:

 //配置数据库的连接字符串
 services.AddDbContext<MyContext>(option =>
 { 
  //option.UseSqlServer("Server =(localdb)\\MSSQLLocalDB;Database=AspEFCoreDemo; Trusted_Connection=True");
                option.UseSqlServer(_configuration.GetConnectionString("DefaultConnectionString"));
});

需要将数据库连接字符串所在项目设置为启动项 即 AspEFCore.Web设置为启动项.