无法执行查询，因为datetime不会转换为字符串c＃/ MSSQL

Question

I have this attempt to execute a query:

 hmrSingle = dbMngr.Set<HistoryMessagesRequested>().Where(x => x.dateregistration == msgv.DtRicezione && x.val == msgv.value && x.parameter == dmf.Description && x.DeviceID == ms.IDDevice).FirstOrDefault();

dateregistration and DtRicezione are both declared as DateTime? into the database context and they're "datetime" into MSSQL tables too.

I can't figure out why this problem is continuously present.

Answer 1

Any time you are using a nullable value type you need to use .value to get its value. Try:

hmrSingle = dbMngr.Set<HistoryMessagesRequested>().Where(x => x.dateregistration.value == msgv.DtRicezione.value && x.val == msgv.value && x.parameter == dmf.Description && x.DeviceID == ms.IDDevice).FirstOrDefault();