依赖项：

Microsoft.EntityFrameworkCore

Microsoft.EntityFrameworkCore.Design

​Microsoft.EntityFrameworkCore.SqlServer​

​Microsoft.EntityFrameworkCore.Tools
MySql.Data
MySql.EntityFrameworkCore
Microsoft.AspNetCore.Mvc
​

1、创建DbContext文件：

public class SqlDbContext: DbContext
    {

//方式一：

//public SqlDbContext(DbContextOptions<SqlDbContext> options) : base(options) { } 

        public SqlDbContext()
        {
            //如果要访问的数据库存在，则不做操作，如果不存在，会自动创建所有数据表和模式
            Database.EnsureCreated();
        }
        protected override void OnModelCreating(ModelBuilder builder)
        {
            base.OnModelCreating(builder);
        }

//方式二：
        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            //SQL Server/Azure SQL 数据库、SQLite、Azure Cosmos DB、MySQL、PostgreSQL数据库连接
            IConfiguration congifuration = new ConfigurationBuilder().SetBasePath(Directory.GetCurrentDirectory()).AddJsonFile("appsettings.json").Build();
            string connStr = congifuration["ConnectionStrings:MySqlConnection"];
            optionsBuilder.UseMySQL(connStr); //使用MySQL数据库
        }

        /// <summary>
        /// sys
        /// </summary>
        public DbSet<Customer> Customer { get; set; }

    }

2、配置“appsettings.json”文件：

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Warning",
      "Microsoft.Hosting.Lifetime": "Information"
    }
  },
  "AllowedHosts": "*",
  "ConnectionStrings": { "MySqlConnection": "Server=localhost;Database=DwDB;User ID=root;password=root;port=3306;sslmode=none;CharSet=utf8" }
}

3、配置“Startup.cs"文件（注意：我们重载了OnConfiguring，在这里不需要如下配置）：

public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllersWithViews();
            //使用MySQL数据库方式一使用
            //services.AddDbContextPool<SqlDbContext>(options => options.UseMySQL(Configuration.GetConnectionString("MySqlConnection")));

            //使用MSSQL数据库
           // services.AddDbContext<SqlDbContext>(options => options.UseSqlServer(Configuration.GetConnectionString("MSSqlConnection")));
        }

3、使用方式如下：

private readonly SqlDbContext db = new SqlDbContext();
        public List<Customer> GetList()
        {
            var aa= db.Customer.ToList();
            return aa;           

        }

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