NetCore下使用EFCore CodeFirst 方式创建更新数据库

项目结构图如下：

IService 主要是接口 ，Service 是服务处理，Models 各种数据实体，Repository 数据访问处理

1、首先在Models 项目下创建类

namespace Models
{
    [Table("User")]
   public class BaseUser
    {
        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int Id { get; set; }
        [MaxLength(20)]
        public string UserName { get; set; }
    }
}

namespace Models
{
    [Table("Role")]
    public class Role
    {
        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int Id { get; set; }
        [MaxLength(20)]
        [Required]
        public string RoleName { get; set; }
        
    }
}

namespace Models
{
    [Table("UserRole")]
   public class UserRole
    {
        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int Id { get; set; }
        [ForeignKey("UserID")]
        public virtual BaseUser User { get; set; }
        [ForeignKey("RoleID")]
        public virtual Role Role { get; set; }

    }
}

2、在 Repository 项目下创建DbContext类

namespace Repository
{
    public partial class MiveDb:DbContext
    {
        public MiveDb()
        {

        }

        public MiveDb(DbContextOptions<MiveDb> options)
            :base(options)
        {

        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            base.OnModelCreating(modelBuilder);
        }

        public virtual DbSet<Movie> Movie { get; set; }
        public virtual DbSet<BaseUser> User { get; set; }
        public virtual DbSet<Role> Role { get; set; }
        public virtual DbSet<UserRole> UserRole { get; set; }
    }
}

3、在Web项目下的appsettings.json文件中添加数据库连接字符串，添加后如下：

{
  "Logging": {
    "LogLevel": {
      "Default": "Warning"
    }
  },
  "AllowedHosts": "*",
  "ConnectionStrings": {
    "DefaultConnection": "Data Source=127.0.0.1;Initial Catalog=MovieDb;user id=sa;password=sa@123;Max Pool Size=512;Min Pool Size=5"
  }
}

4、在webapp 配置 Startup.cs 下进行配置

　　4.1  创建一个方法用于程序集注入

　　　　

 /// <summary>  
        /// 自动注册服务——获取程序集中的实现类对应的多个接口
        /// </summary>
        /// <param name="services">服务集合</param>  
        /// <param name="assemblyName">程序集名称</param>
        public void AddAssembly(IServiceCollection services, string assemblyName)
        {
            if (!String.IsNullOrEmpty(assemblyName))
            {
                Assembly assembly = Assembly.Load(assemblyName);
                List<Type> ts = assembly.GetTypes().Where(u => u.IsClass && !u.IsAbstract && !u.IsGenericType).ToList();
                foreach (var item in ts.Where(s => !s.IsInterface))
                {
                    var interfaceType = item.GetInterfaces();
                    if (interfaceType.Length == 1)
                    {
                        services.AddTransient(interfaceType[0], item);
                    }
                    if (interfaceType.Length > 1)
                    {
                        services.AddTransient(interfaceType[1], item);
                    }
                }
            }
        }
   

　　　　4.2  在 Startup.cs 中 ConfigureServices 方法中添加注入

 AddAssembly(services, "IService");
            AddAssembly(services, "Service");
            services.AddDbContext<MiveDb>(options =>
            {
                var connection = Configuration.GetConnectionString("DefaultConnection");
                options.UseSqlServer(
                    connection
                    );
            });

　　　　4.3 按照项目需要，引用个项目

5、打开命令行控制台，切换到 Repository 项目

PM> Add-Migration FirstMigration

执行以上命令，备注：

FirstMigration  名字任意取

中间可能会遇见各种问题，主要是各个项目之间的引用就可以解决

执行成功后，Repository 中会出现 如图

 但是发现在TestMovieDB.cs这个文件中有一个错误  

SqlServerValueGenerationStrategy 缺少引用

namespace Repository.Migrations
{
    public partial class TestMovieDB : Migration
    {
        protected override void Up(MigrationBuilder migrationBuilder)
        {
            migrationBuilder.CreateTable(
                name: "Movie",
                columns: table => new
                {
                    Id = table.Column<int>(nullable: false)
                        .Annotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn),
                    Title = table.Column<string>(maxLength: 50, nullable: true),
                    Info = table.Column<string>(maxLength: 500, nullable: true),
                    CreateTime = table.Column<DateTime>(nullable: false)
                },
                constraints: table =>
                {
                    table.PrimaryKey("PK_Movie", x => x.Id);
                });

            migrationBuilder.CreateTable(
                name: "Role",
                columns: table => new
                {
                    Id = table.Column<int>(nullable: false)
                        .Annotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn),
                    RoleName = table.Column<string>(maxLength: 20, nullable: false)
                },
                constraints: table =>
                {
                    table.PrimaryKey("PK_Role", x => x.Id);
                });

            migrationBuilder.CreateTable(
                name: "User",
                columns: table => new
                {
                    Id = table.Column<int>(nullable: false)
                        .Annotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn),
                    UserName = table.Column<string>(maxLength: 20, nullable: true)
                },
                constraints: table =>
                {
                    table.PrimaryKey("PK_User", x => x.Id);
                });

            migrationBuilder.CreateTable(
                name: "UserRole",
                columns: table => new
                {
                    Id = table.Column<int>(nullable: false)
                        .Annotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn),
                    UserID = table.Column<int>(nullable: true),
                    RoleID = table.Column<int>(nullable: true)
                },
                constraints: table =>
                {
                    table.PrimaryKey("PK_UserRole", x => x.Id);
                    table.ForeignKey(
                        name: "FK_UserRole_Role_RoleID",
                        column: x => x.RoleID,
                        principalTable: "Role",
                        principalColumn: "Id",
                        onDelete: ReferentialAction.Restrict);
                    table.ForeignKey(
                        name: "FK_UserRole_User_UserID",
                        column: x => x.UserID,
                        principalTable: "User",
                        principalColumn: "Id",
                        onDelete: ReferentialAction.Restrict);
                });

            migrationBuilder.CreateIndex(
                name: "IX_UserRole_RoleID",
                table: "UserRole",
                column: "RoleID");

            migrationBuilder.CreateIndex(
                name: "IX_UserRole_UserID",
                table: "UserRole",
                column: "UserID");
        }

        protected override void Down(MigrationBuilder migrationBuilder)
        {
            migrationBuilder.DropTable(
                name: "Movie");

            migrationBuilder.DropTable(
                name: "UserRole");

            migrationBuilder.DropTable(
                name: "Role");

            migrationBuilder.DropTable(
                name: "User");
        }
    }
}

 哈哈，没关系，这个问题明显是缺少 对dll 的引用，我们引用即可

接着引用 Microsoft.EntityFrameworkCore.SqlServer  dll，版本根据实际需求引用 

这个时候虽然成功了，但是数据库中的数据还未被创建

6、执行数据库更新操作

 PM> Update-Database -Verbose 

 出现这些就表示成功了，接着我们看数据库

此时数据库已经创建好了！

7、有没有发现数据库的名称和我们DbContext  名字一样

具体啥原因没仔细研究