var db = new SqlSugarClient(new List<ConnectionConfig>()
{
 new ConnectionConfig(){ConfigId="0",DbType=DbType.SqlServer,ConnectionString=..,IsAutoCloseConnection=true},
 new ConnectionConfig(){ConfigId="1",DbType=DbType.MySql,ConnectionString=..,IsAutoCloseConnection=true  }
});

 if(!db.IsAnyConnection(configId))//当前上下文不存在则添加
    db.AddConnection(new ConnectionConfig{
                           DbType = DbType.SqlServer,ConfigId = "1", 
                IsAutoCloseConnection = true,
                ConnectionString = 。。 });
//开启事务
try {
 //db我们称为主Db 
 db.BeginTran(); //开启多库 （db.Ado.BeginTran是单库事务）事务支持单库和多库
 
 db.GetConnection("1").Insertable(new Order()//var childDb=db.GetConnection(1);我们称为子DB，子DB不具有租户方法，具有单当库操作方法
 {
   CreateTime = DateTime.Now,
   CustomId = 1,
   Name = "a",
   Price = 1
 }).ExecuteCommand();
 
 db.GetConnection("2").Insertable(new Order()
 {
   CreateTime = DateTime.Now,
   CustomId = 1,
   Name = "a",
   Price = 1
 }).ExecuteCommand();
 
 //提交事务 
 db.CommitTran();  
 
}
catch(Exception ex)
{
  //回滚事务
  db.Rollback();
}

 [Tenant("db2")]//在类的特性设置当前类属于哪个库
  public class OrderItem
 {
            [SqlSugar.SugarColumn(IsPrimaryKey = true, IsIdentity = true)]
            public int ItemId { get; set; }
            public int OrderId { get; set; }
            public decimal? Price { get; set; }
            [SqlSugar.SugarColumn(IsNullable = true)]
            public DateTime? CreateTime { get; set; }
            [Navigate(NavigateType.OneToOne,nameof(OrderId))] //设置关系 对应Order表主键
            public Order Order { get; set; }
 }



//通过ConfigId进行区分是哪个库
var db = new SqlSugarClient(new List<ConnectionConfig>()
{
  new ConnectionConfig(){ConfigId="db1",DbType=DbType.Sqlite,ConnectionString="DataSource=/Db_OrderDb.sqlite",IsAutoCloseConnection=true},
  new ConnectionConfig(){ConfigId="db2",DbType=DbType.Sqlite,ConnectionString="DataSource=/Db_OrderItemDb.sqlite",IsAutoCloseConnection=true }
});

//通过实体类特性[Tenant("db2")]自动映射不同数据库进行查询
var list=db.QueryableWithAttr<OrderItem>()
.Includes(z => z.Order)
.ToList(); //1行代码就搞定了2个库联表查询

 [Tenant("db1")]//指定是db1  (OrderItem类设置为 db2)
  public class Order
  {
            [SugarColumn(IsPrimaryKey = true, IsIdentity = true)]
            public int Id { get; set; }
            public string Name { get; set; }
            public decimal Price { get; set; }
            [SugarColumn(IsNullable = true)]
            public DateTime CreateTime { get; set; }
            [SugarColumn(IsNullable = true)]
            public int CustomId { get; set; }
            [Navigate(NavigateType.OneToMany, nameof(OrderItem.OrderId))]//
            public List<OrderItem> Items { get; set; }
  }

  var list = db.QueryableWithAttr<Order>()
                    .Includes(z => z.Items)//跨库一对多
                    .ToList();

 var db = new SqlSugarClient(new List<ConnectionConfig>()
    {
        new ConnectionConfig(){ConfigId="A",DbType=DbType.Sqlite,ConnectionString="DataSource=/A_DB.sqlite",IsAutoCloseConnection=true},
        new ConnectionConfig(){ConfigId="B",DbType=DbType.Sqlite,ConnectionString="DataSource=/B_DB.sqlite",IsAutoCloseConnection=true  },
        new ConnectionConfig(){ConfigId="AB",DbType=DbType.Sqlite,ConnectionString="DataSource=/AB_DB.sqlite",IsAutoCloseConnection=true  }
  });p　

       [Tenant("A")]//指定为A库
        public partial class OperatorInfo
        {
            /// <summary>
            /// 主键
            /// </summary>
            [SugarColumn(IsPrimaryKey = true)]
            public int id { get; set; }

            /// <summary>
            /// 姓名
            /// </summary>
            public string realname { get; set; }

            /// <summary>
            /// 多角色
            /// </summary>
            [Navigate(typeof(OptRole), nameof(OptRole.operId), nameof(OptRole.roleId))]//配置导航
            public List<Role> Roles { get; set; }
        }


        [Tenant("B")]//指定为B库
        public partial class Role
        {
            /// <summary>
            /// 角色
            /// </summary>
            [SugarColumn(IsPrimaryKey = true )]
            public int id { get; set; }

            /// <summary>
            /// 角色名称
            /// </summary>
            public string name { get; set; }
 
        }
 

        [Tenant("AB")]//指定为AB库
        public partial class OptRole
        {
            /// <summary>
            /// 
            /// </summary>
            [SugarColumn(IsPrimaryKey = true)]
            public int id { get; set; }

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

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


        }

//3个库3个表进行多对多查询
var x=db.QueryableWithAttr<OperatorInfo>()
.Includes(z => z.Roles).ToList();

 var list =db.GetConnection("db1").Queryable<OrderItem>()//Orderitem是db1
                .CrossQuery(typeof(Order), "db2")//Order是db2
                .Includes(z => z.Order)
                .ToList();