ASP.NET Core通过EF Core连接数据库

2021-07-02 04:51:28

使用EF Core的Code First模式,通过迁移来同步数据库与模型.

环境: JetBrains Rider Window10 .NET5

一. 创建项目

使用JetBrains Rider创建一个web api项目
使用NuGet安装依赖包
- Microsoft.EntityFrameworkCore
- Microsoft.EntityFrameworkCore.Tools
- Microsoft.EntityFrameworkCore.SqlServer 此依赖包根据使用的数据库安装相应的包, 这里使用的是SQL Server

创建数据库上下文

在项目中建立一个Data文件夹，创建一个类TestDBContext

using Microsoft.EntityFrameworkCore;

namespace Test.Data
{
    public class TestDBContext : DbContext
    {
        public TestDBContext(DbContextOptions<TestDBContext> options) : base(options){}
    }
}

创建数据模型

在项目中建立一个Models文件夹，创建部门类Department, 员工类Personnel

using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace Test.Models
{
    /// <summary>
    /// 部门类
    /// </summary>
    public class Department
    {
        [Key] // 主键
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]  //设置自增
        public int Id { get; set; }
        
        [Required]
        [MaxLength(50)]
        public string Name { get; set; }

        // Department 与 Personnel 一对多
        public ICollection<Personnel> Personnels { get; set; } = new List<Personnel>();
    }
}

using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace Test.Models
{
    /// <summary>
    /// 员工类
    /// </summary>
    public class Personnel
    {
        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int Id { get; set; }
        
        [Required]
        [MaxLength(50)]
        public string Name { get; set; }
        
        public int Age { get; set; }
        
        [ForeignKey("Department")] // 外键
        public int DepartmentId { get; set; }
    }
}

在之前创建的数据库上下文TestDBContext中注册数据模型

using Microsoft.EntityFrameworkCore;
using Test.Models;

namespace Test.Data
{
    public class TestDBContext : DbContext
    {
        public TestDBContext(DbContextOptions<TestDBContext> options) : base(options){}
        
        // 注册数据模型
        // 模型集的名称与对应的表名相同
        public DbSet<Department> Departments { get; set; }
        public DbSet<Personnel> Personnels { get; set; }
    }
}

在appsettings.json中添加数据库连接字符串

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Warning",
      "Microsoft.Hosting.Lifetime": "Information"
    }
  },
  "AllowedHosts": "*",
  "connectionStrings": {
    "SqlServerContext": "Data Source=服务器名;Initial Catalog=数据库名; User Id=用户名;Password=密码"
  }
}

在Startup中注册数据库上下文TestDBContext

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.OpenApi.Models;
using Test.Data;

namespace Test
{
    public class Startup
    {
        // 注入 IConfiguration:有关配置文件最底层的一个接口类型
        public Startup(IConfiguration configuration)
        {
            _Configuration = configuration;
        }

        private IConfiguration _Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllers();
            services.AddSwaggerGen(c => { c.SwaggerDoc("v1", 
                new OpenApiInfo {Title = "Test", Version = "v1"}); });
            // 注册数据库上下文
            // _Configuration["connectionStrings:SqlServerContext"] 获取数据库连接字符串
            services.AddDbContext<TestDBContext>(option
                => option.UseSqlServer(_Configuration["connectionStrings:SqlServerContext"]));
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
                app.UseSwagger();
                app.UseSwaggerUI(c => c.SwaggerEndpoint("/swagger/v1/swagger.json", "Test v1"));
            }

            app.UseHttpsRedirection();

            app.UseRouting();

            app.UseAuthorization();

            app.UseEndpoints(endpoints => { endpoints.MapControllers(); });
        }
    }
}

迁移
- 打开Terminal窗口或者cmd进入项目根目录执行迁移命令: dotnet ef migrations add 本次迁移的名称
- 如果未安装dotnet ef, 会无法执行
- 安装全局dotnet ef
- 再次执行迁移命令
- 迁移成功后, 项目中有一个Migrations目录, 保存着每次迁移的记录
更新数据库
- 执行dotnet ef database update
- 数据库更新成功, 数据库就已经创建好了
- 当数据模型发生改变时, 只用再次执行迁移/更新数据库

二. 添加初始数据

在数据上下文TestDBContext中重写OnModelCreating方法

using System.Collections.Generic;
using Microsoft.EntityFrameworkCore;
using Test.Models;

namespace Test.Data
{
    public class TestDBContext : DbContext
    {
        public TestDBContext(DbContextOptions<TestDBContext> options) : base(options){}
        
        // 注册数据模型
        // 模型集的名称与对应的表名相同
        public DbSet<Department> Departments { get; set; }
        public DbSet<Personnel> Personnels { get; set; }

        // 控制数据库和模型映射, 通过它可以自定义映射关系
        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Department>()
                .HasData(new List<Department>()
                {
                    new Department() {Id = 1, Name = "人力资源部"},
                    new Department() {Id = 2, Name = "技术部"}
                });
            modelBuilder.Entity<Personnel>()
                .HasData(new List<Personnel>()
                {
                    new Personnel() {Id = 1, Name = "张三", Age = 23, DepartmentId = 2},
                    new Personnel() {Id = 2, Name = "李四", Age = 20, DepartmentId = 1},
                    new Personnel() {Id = 3, Name = "王五", Age = 25, DepartmentId = 2}
                });
            base.OnModelCreating(modelBuilder);
        }
    }
}

迁移, 更新数据库

ASP.NET Core通过EF Core连接数据库

码农公寓

一. 创建项目

二. 添加初始数据

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