Linq查询返回匿名类型无法转换为SCADA_DATA_Truncated类列表报错

你遇到的类型转换报错由两个问题共同导致：

1. select new { ... }语法生成的是匿名类型实例，和你自定义的SCADA_DATA_Truncated类没有任何兼容转换关系，无法直接互转
2. 你尝试将整个List<匿名类型>强制转换为单个SCADA_DATA_Truncated对象的写法本身存在语法错误

只需要在select子句中直接实例化你自定义的SCADA_DATA_Truncated类即可，EF可以正常解析这种属性初始化的写法，DbFunctions.TruncateTime的返回值也刚好匹配你类中COLDATE字段的Nullable<DateTime>类型：

List<SCADA_DATA_Truncated> dataResults = (from b in a2Entity.SCADA_DATA
                                           where DbFunctions.TruncateTime(b.COLDATE) >= dateCheck1 
                                           && DbFunctions.TruncateTime(b.COLDATE) <= dateCheck2
                                           && whereInAcode.Contains(b.acode) 
                                           && whereInLoc.Contains(b.LOCCODE)
                                           select new SCADA_DATA_Truncated // 这里改为实例化你的自定义类
                                           {
                                               COLDATE = DbFunctions.TruncateTime(b.COLDATE),
                                               acode = b.acode,
                                               LOCCODE = b.LOCCODE,
                                               RESULT = b.RESULT,
                                               analyte = b.analyte
                                           }
                                       ).ToList();

你可以对查询条件做小优化，避免重复调用DbFunctions.TruncateTime：

List<SCADA_DATA_Truncated> dataResults = (from b in a2Entity.SCADA_DATA
                                           let truncDate = DbFunctions.TruncateTime(b.COLDATE)
                                           where truncDate >= dateCheck1 
                                           && truncDate <= dateCheck2
                                           && whereInAcode.Contains(b.acode) 
                                           && whereInLoc.Contains(b.LOCCODE)
                                           select new SCADA_DATA_Truncated
                                           {
                                               COLDATE = truncDate,
                                               acode = b.acode,
                                               LOCCODE = b.LOCCODE,
                                               RESULT = b.RESULT,
                                               analyte = b.analyte
                                           }
                                       ).ToList();

内容的提问来源于stack exchange，提问作者Julius Alexander