Cannot set property value to target type from sqldatareader type

Question

List<T> returnList = new List<T>();
conn.Open();
SqlCommand sCmd = new SqlCommand(query, conn);
SqlDataReader dataReader = sCmd.ExecuteReader();
T t = new T();
PropertyInfo[] p = o.GetType().GetProperties();
while(dataReader.Read())
{
    for (int i = 0; i < p.Length; i++)
    {
        Console.WriteLine(p[i].GetValue(t)+" "+p[i].PropertyType+" 
        "+dataReader[i].GetType());
        p[i].SetValue(dataReader[i], t);
    }
    returnList.Add(t);
}
return returnList;

I want to set the value of specific property at run time from sqldatareader object. But i am getting an exception of target type mismatch even though both references are of the same type

At which line to you get this exception ? How do you know that your columns in your datareader are in the same order than your properties ? — Martin Verjans
– Martin Verjans, Commented Oct 12, 2017 at 5:53
the line in which i'm setting the value and I've written a class the order in which my columns are placed in the table — Sohel Ahmed
– Sohel Ahmed, Commented Oct 12, 2017 at 5:57
Could you add in your code the method signature ? (public/private List<T> myMethodName...) — Martin Verjans
– Martin Verjans, Commented Oct 12, 2017 at 6:05

Martin Verjans · Accepted Answer · 2017-10-12 06:17:20Z

1

You have two problems here. The main one is that you make a wrong call to SetValue().

From MSDN:

public void SetValue(object obj, object value)

So actually you are calling the method with the wrong placed arguments. Do this and it should be fine:

p[i].SetValue(t, dataReader[i]);

The second problem that you will encounter is that at the end your list will contain only the same object, because you create a new object only once (T t = new T();. To solve it, you must place this line inside your while loop.

Also, use using for cleaner code and because you should dispose your command at the end... And close your connection.

All in all, this is the final code:

List<T> returnList = new List<T>();
conn.Open();
using (SqlCommand sCmd = new SqlCommand(query, conn))
{
    SqlDataReader dataReader = sCmd.ExecuteReader();
    PropertyInfo[] p = o.GetType().GetProperties();
    while(dataReader.Read())
    {
        T t = new T();
        for (int i = 0; i < p.Length; i++)
        {
            Console.WriteLine(p[i].GetValue(t)+" "+p[i].PropertyType+" "+dataReader[i].GetType());
            p[i].SetValue(t, dataReader[i]);
        }
        returnList.Add(t);
    }
}
conn.Close();
return returnList;

answered Oct 12, 2017 at 6:17

Martin Verjans

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2 Comments

Sohel Ahmed Over a year ago

Thanks that helped

Martin Verjans Over a year ago

@SohelAhmed If this answers your question, please mark it as the answer (the check mark next to the top of the answer). That way others will see that this question is answered.

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