错误:LINQ to Entities不能识别'Int32 ToInt32方法

我想在linq查询中将字符串转换为整型，并得到以下错误

错误:LINQ to Entities不识别Int32 ToInt32方法

数据库字段id = varchar

var AllArea = (from arr in dbcontext.Areas
               join city in dbcontext.Cities on Convert.ToInt32(arr.arID) equals city.cityID
               select new
               {
                   arr.arID,
                   arr.AreaName,
                   city.cityID,
                   city.cityName
               }).ToList();