LINQ字符串向datetime 转换时失败的处理方法

from j in system.jhzd
where j.dwbm.ToString().Trim() == branchcode.ToString().Trim()
&& Convert.ToDateTime(j.yearmonth.ToString().Trim()).CompareTo(Convert.ToDateTime(timeFrom)) >= 0
&& Convert.ToDateTime(j.yearmonth.ToString().Trim()).CompareTo(Convert.ToDateTime(timeTo)) <= 0
join b in system.t_sys_Branch
on j.dwbm.ToString().Trim() equals b.BranchCode
join c in system.T_CWLB
on j.xmlb.ToString().Trim() equals c.ID
select new
{
BranchName = b.BranchName,
category = c.CWMC,
money = j.je,
comefrom = j.zjly,
time = j.yearmonth,
zhaiyao = j.zhaiyao,
}