（Entity Framework Core入门）二、EFCore数据库配置生成

延续上一章节https://www.cnblogs.com/dzw159/p/10646368.html

我们准备将按照AspCore的依赖注入机制获取appsettings.json的数据库参数配置，用以生成数据库（代码先行，appsettings.json的字符串获取，前面记录：https://www.cnblogs.com/dzw159/p/10591238.html）

创建的结构目录如下：

1）建立项目AspEFCore、类库（

AspEFCore.Data-引用 NuGet包：Microsoft.EntityFrameworkCore.SqlServer、

引用项目：AspEFCore.Domain

AspEFCore.Domain）

2）在 AspEFCore.Domain 创建类（City.cs、Provnce.cs）

using System;
using System.Collections.Generic;
using System.Text;

namespace AspEFCore.Domain.Model
{
    /// <summary>
    /// 城市
    /// </summary>
    public class City
    {
        /// <summary>
        /// 编码
        /// </summary>
        public int Id { get; set; }

        /// <summary>
        /// 城市名称
        /// </summary>
        public string Name { get; set; }

        /// <summary>
        /// 邮编
        /// </summary>
        public string AreaCode { get; set; }

        /// <summary>
        /// 所属省份编码
        /// </summary>
        public int ProviedId { get; set; }

        /// <summary>
        /// 省份
        /// </summary>
        public Province Province { get; set; }
    }
}

using System;
using System.Collections.Generic;
using System.Text;

namespace AspEFCore.Domain.Model
{
    /// <summary>
    /// 省份
    /// </summary>
    public class Province
    {
        public Province()
        {
            Cities = new List<City>();
        }

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

        /// <summary>
        /// 省份名称
        /// </summary>
        public string Name { get; set; }

        /// <summary>
        /// 人口
        /// </summary>
        public int Population { get; set; }

        /// <summary>
        /// 城市
        /// </summary>
        public List<City> Cities { get; set; }

    }
}

3）在 AspEFCore.Data 创建数据连接文件 MyContext.cs

using AspEFCore.Domain.Model;
using Microsoft.EntityFrameworkCore;

namespace AspEFCore.Data
{
    public class MyContext:DbContext
    {
        /// <summary>
        /// 外部参数
        /// </summary>
        /// <param name="options">外部传入的配置参数（这样子的话，我们就可以通过外部来控制传入的参数值，用以决定使用哪个数据库）</param>
        public MyContext(DbContextOptions<MyContext> options):base(options)
        {

        }

        public DbSet<City> Cities { get; set; }
        public DbSet<Province> Provinces { get; set; }

        //protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        //{
        //    //使用本地的Windows验证
        //    optionsBuilder.UseSqlServer("Server=(localdb)\\mssqllocaldb;Database=EFCoreDemo;Trusted_Connection=True;");
        //    //base.OnConfiguring(optionsBuilder);
        //}

    }
}

4）创建 AspEFCore.Web（引用项目AspEFCore.Domain、AspEFCore.Data）

5）在 AspEFCore.Web 创建外部数据库参数配置文件 appsettings.json

{
  "Logging": {
    "LogLevel": {
      "Default": "Debug",
      "System": "Information",
      "Microsoft": "Debug"
    }
  },
  "ConnectionStrings": {
    "DefaultConnection": "Server=(localdb)\\mssqllocaldb;Database=AspEFCoreDemo;Trusted_Connection=True;"
  }
}

5）修改 AspEFCore.Web 的 Startup.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using AspEFCore.Data;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;

namespace AspEFCore.Web
{
    public class Startup
    {
        public IConfiguration Configuration { get; }
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        // This method gets called by the runtime. Use this method to add services to the container.
        // For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940
        public void ConfigureServices(IServiceCollection services)
        {
            services.Configure<CookiePolicyOptions>(options => 
            {
                options.CheckConsentNeeded = context => true;
                options.MinimumSameSitePolicy = SameSiteMode.None;
            });

            services.AddMvc().SetCompatibilityVersion(Microsoft.AspNetCore.Mvc.CompatibilityVersion.Version_2_1);

            services.AddDbContext<MyContext>(
                options=>
                {
                    //获取数据连接串
                    //options.UseSqlServer("Server=(localdb)\\mssqllocaldb;Database=AspEFCoreDemo;Trusted_Connection=True;");
                    options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection"));
                });

        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.Run(async (context) =>
            {
                await context.Response.WriteAsync("Hello World!");
            });
        }
    }
}

6）使用程序包管理控制台生成数据（参照https://www.cnblogs.com/dzw159/p/10646368.html 的第5点）

注：

1）默认项目设置成数据Data连接（MyContext.cs）的所在项目，将数据库配置的（AspEFCore.Web）项目设置成启动项

2）碰到一个问题，前面在AspEFCore.Data 中引用的Microsoft.EntityFrameworkCore.SqlServer 版本为2.2.4，后AspEFCore.Web 里面默认有引用这个（创建项目默认引用，但是版本为2.1.1），导致版本不符合，我就将AspEFCore.Data 的Microsoft.EntityFrameworkCore.SqlServer 降成版本2.1.1

7）主键关联操作

①例如：添加一个公司和城市的关联类CityCompany.cs

using System;
using System.Collections.Generic;
using System.Text;

namespace AspEFCore.Domain.Model
{
    public class CityCompany
    {

        /// <summary>
        /// 城市Id
        /// </summary>
        public int CityId { get; set; }

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

        /// <summary>
        /// 
        /// </summary>
        public int CompanyId { get; set; }

        /// <summary>
        /// 
        /// </summary>
        public Company Company { get; set; }
    }
}

②修改和添加类

using System;
using System.Collections.Generic;
using System.Text;

namespace AspEFCore.Domain.Model
{
    /// <summary>
    /// 城市
    /// </summary>
    public class City
    {
        /// <summary>
        /// 编码
        /// </summary>
        public int Id { get; set; }

        /// <summary>
        /// 城市名称
        /// </summary>
        public string Name { get; set; }

        /// <summary>
        /// 邮编
        /// </summary>
        public string AreaCode { get; set; }

        /// <summary>
        /// 所属省份编码
        /// </summary>
        public int ProviedId { get; set; }

        /// <summary>
        /// 省份
        /// </summary>
        public Province Province { get; set; }

        public List<CityCompany> CityCompanies{ get; set; }

        public Mayor Mayor { get; set; }

    }
}

using System;
using System.Collections.Generic;
using System.Text;

namespace AspEFCore.Domain.Model
{
    /// <summary>
    /// 公司
    /// </summary>
    public class Company
    {

        public Company()
        {
            CityCompanies = new List<CityCompany>();
        }

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

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

        /// <summary>
        /// 成立时间
        /// </summary>
        public DateTime EstablishDate { get; set; }

        /// <summary>
        /// 法人
        /// </summary>
        public string LegalPerson { get; set; }

        public List<CityCompany> CityCompanies { get; set; }
    }
}

using System;
using System.Collections.Generic;
using System.Text;

namespace AspEFCore.Domain.Model
{
    public enum Gender
    {
        /// <summary>
        /// 女
        /// </summary>
        Female = 0,

        /// <summary>
        /// 男
        /// </summary>
        Male = 1
    }
}

③到Data里的OnModelCreating进行关联（添加红色部分，明确配置关系）

using AspEFCore.Domain.Model;
using Microsoft.EntityFrameworkCore;

namespace AspEFCore.Data
{
    public class MyContext:DbContext
    {
        /// <summary>
        /// 外部参数
        /// </summary>
        /// <param name="options">外部传入的配置参数（这样子的话，我们就可以通过外部来控制传入的参数值，用以决定使用哪个数据库）</param>
        public MyContext(DbContextOptions<MyContext> options):base(options)
        {

        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {

　　　　　　　　//添加数据
　　　　　　　　//modelBuilder.Entity<Province>().HasData(
　　　　　　　　// new Province
　　　　　　　　// {
　　　　　　　　// Id = 20,
　　　　　　　　// Name = "福建省",
　　　　　　　　// Population = 6000
　　　　　　　　// }
　　　　　　　　// );

            modelBuilder.Entity<City>()
                .HasOne(x => x.Province).WithMany(x => x.Cities)
                .HasForeignKey(x => x.ProviedId);

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

            modelBuilder.Entity<CityCompany>()
                .HasOne(x => x.City).WithMany(x => x.CityCompanies).HasForeignKey(x=>x.CityId);

            modelBuilder.Entity<CityCompany>()
                .HasOne(x => x.Company).WithMany(x => x.CityCompanies).HasForeignKey(x => x.CompanyId);

            modelBuilder.Entity<Mayor>()
                .HasOne(x => x.City).WithOne(x => x.Mayor).HasForeignKey<Mayor>(x => x.CityId);
        }

        public DbSet<City> Cities { get; set; }
        public DbSet<Province> Provinces { get; set; }
        public DbSet<CityCompany> CityCompanies { get; set; }
        public DbSet<Company> Companies { get; set; }
        public DbSet<Mayor> Mayors { get; set; }

        //protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        //{
        //    //使用本地的Windows验证
        //    optionsBuilder.UseSqlServer("Server=(localdb)\\mssqllocaldb;Database=EFCoreDemo;Trusted_Connection=True;");
        //    //base.OnConfiguring(optionsBuilder);
        //}

    }
}

using System;
using System.Collections.Generic;
using System.Text;

namespace AspEFCore.Domain.Model
{
    /// <summary>
    /// 省份
    /// </summary>
    public class Province
    {
        public Province()
        {
            Cities = new List<City>();
        }

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

        /// <summary>
        /// 省份名称
        /// </summary>
        public string Name { get; set; }

        /// <summary>
        /// 人口
        /// </summary>
        public int Population { get; set; }

        /// <summary>
        /// 城市
        /// </summary>
        public List<City> Cities { get; set; }

    }
}