尝试从数据读取器读取值时发生转换错误

Question

I am trying to read value from data reader based on column name but i am not getting in what data type(int,double,decimal) i should read that value because that column will have aggregate operations like sum,average,count,min,max etc...

I am getting below error when i am trying to data reader value in double datatype :

double unitPrice = dr.GetDouble(0); // index of my column whose value i want to read from data reader

Error : Specified cast is not valid

Sql Query :

select sum([UnitPrice]) AS unitPrice from [Sales].[SalesOrderDetail]

Further i have some calculations on this unitPrice variable so i am not getting what will be the best way to read this value and in what datatype?

Because of calculations on unitPrice variable i am not taking it as string otherwise i have to parse it everywhere in my calculations in double

Answer 1

I was having the same issue, using strong typing worked for me:

public Double unitPrice = Convert.ToDouble(dr["unitPrice"]);

or if you already know the index of the column you want to read:

public Double unitPrice = Convert.ToDouble(dr(0));