用linq替换字符串

Question

I have this query it is suppose to get the ip addresses and match them to the DeviceUIDs which is located on another table. I am looking to replace the "." in the IP Address with "0" but the way I have the code running right now it does not replace the "."

Can anyone help me with this please.

 var etjoin = (from e in dxlXs.AsEnumerable()
              join t in tstarresults on new String(e.Field<String>("Ip Address").Replace(".","0").ToArray()) equals t.DeviceUID
              into leftjointable
              from x in leftjointable.DefaultIfEmpty()
              select new ATTModel
              {
                  ATTIP = e != null ? e.Field<String>("IP Address") : "N/A",
                  ATTICCID = e != null ? e.Field<String>("ICCID") : "N/A",
                  ATTSTATUS = e != null ? e.Field<String>("SIM Status") : "N/A",
                  ATTSession = e != null ? e.Field<String>("In Session") : "N/A",
                  ATTActivated = e != null ? e.Field<String>("Activated") : "N/A",
                  IP = x != null ? x.DeviceUID : "N/A",
                  VehicleName = x != null ? x.VehicleName : "N/A",
                  VehicleGroupName = x != null ? x.VehicleGroupName : "N/A",
                  PhoneNumber = x != null ? x.UserDefinedColumn2 : "N/A"
              }).ToList();

Answer 1

First String.Replace returns a new string with replaced characters, so you don't need the constructor new String(char[]) ( ctor ).

Second there is nothing explicit wrong with the string replacement. eg "127.0.0.1".Replace(".","0") returns "127000001" So you have to be more precise on what is "wrong".

Third your logic is a left join so if you're expecting null values for e when creating your ATTModel you have to check for null in e.Field<String>("Ip Address") too. (one can guess dxlXs is a DataTable or a DataSet thus the rows are not likely being null )

Answer 2

With your replace in the Join , you are creating a new string just for the purposes of making the join. That string is assigned or stored anywhere, so e.Field<String>("Ip Address") will still have the same value (with the dots).

If you need ATTIP to have the value with the . replaced with 0 (although I'm not sure that really makes sense), then you could do something like:

 var etjoin = (from e in dxlXs.AsEnumerable()
              let temp = e != null ? e.Field<String>("Ip Address").Replace(".","0") : "N/A"
              join t in tstarresults on temp equals t.DeviceUID
              into leftjointable
              from x in leftjointable.DefaultIfEmpty()
              select new ATTModel
              {
                  ATTIP = temp,
                  //...
              }).ToList();