Linq 想实现Left Join 功能，老抛异常，各位大牛帮看看

static void Main(string[] args)
        {
            DataTable dt1 = new DataTable();
            dt1.Columns.Add("id", typeof(int));
            dt1.Columns.Add("name", typeof(string));
            DataTable dt2 = new DataTable();
            dt2.Columns.Add("id", typeof(int));
            dt2.Columns.Add("sex", typeof(string));
            for (int i = 0; i < 3; i++)
            {
                DataRow dr = dt1.NewRow();
                dr["id"] = i;
                dr["name"] = "table1 " + i;
                dt1.Rows.Add(dr);
            }
            for (int i = 1; i < 4; i++)
            {
                DataRow dr = dt2.NewRow();
                dr["id"] = i;
                dr["sex"] = "sex  " + i;
                dt2.Rows.Add(dr);
            }
            //var q = dt1.AsEnumerable().Join(dt2.AsEnumerable(), dt1key => dt1key.Field<int>("id"),
            //            dt2key => dt2key.Field<int>("id"), (dt1key, dt2key) => new
            //{
            //    id = dt1key.Field<int>("id"),
            //    name = dt1key.Field<string>("name"),
            //    sex = dt2key.Field<string>("sex") 
            //});
            var q = from member in dt1.AsEnumerable()
                    join club in dt2.AsEnumerable() on member.Field<int>("id") equals club.Field<int>("id") 
 
                        into ret
                    from source in ret.DefaultIfEmpty()
                    select new
                    {
                        id = source.Field<int>("id"),
                        name = source.Field<string>("name"),
                        sex = (source==null?string.Empty: source.Field<string>("sex"))
                    };
            foreach (var obj in q)
            {
                Console.WriteLine(
                    "{0} - {1} - {2}",
                    obj.id,
                    obj.name,
                    obj.sex);
            }
        }

System.ArgumentNullException was unhandled
HResult=-2147467261
Message=值不能为 null。
参数名: row
Source=System.Data.DataSetExtensions
ParamName=row
StackTrace:
在 System.Data.DataRowExtensions.Field[T](DataRow row, String columnName)
在 ConsoleApplication1.Program.<Main>b__6(<>f__AnonymousType0`2 <>h__TransparentIdentifier0, DataRow source) 位置 E:\WorkSpace\DotNet\Local\ConsoleApplication1\ConsoleApplication1\Program.cs:行号 44
在 System.Linq.Enumerable.<SelectManyIterator>d__31`3.MoveNext()
在 ConsoleApplication1.Program.Main(String[] args) 位置 E:\WorkSpace\DotNet\Local\ConsoleApplication1\ConsoleApplication1\Program.cs:行号 50
InnerException:
linq left?join
[解决办法]
ArgumentNullException,有控制，linq选出数据可能遇到无数据的情况，这个你要控制一下
[解决办法]
try

 var q = from member in dt1.AsEnumerable()
                    join club in dt2.AsEnumerable() on member.Field<int>("id") equals club.Field<int>("id") 
 
                        into ret
                    from source in ret.DefaultIfEmpty()
                    select new
                    {
                        id = member.Field<int>("id"),
                        name =member .Field<string>("name"),
                        sex = (source == null ? string.Empty : source.Field<string>("sex"))
                    };