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General method of reading data from DataReader

I am currently using this method to read data from a DataReader -

private T GetValue<T>(object obj)
{
    if (typeof(DBNull) != obj.GetType())
    {
        return (T)obj;
    }
    return default(T);
}

method call above -

GetValue<int>(dataReader["columnName1"])
GetValue<string>(dataReader["columnName2"])
GetValue<float>(dataReader["columnName3"])

However, this fails if columnName3it matters as 7200000with an error. Invalid Cast Exception.

I want to change my method to replace -

return (T)obj;

with

return (T)Convert.ChangeType(obj, typeof(T));

But we look forward to a better way, as this change will include casting twice.
Any better ideas?

Thank!

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2 answers

, , , . , , db , .

, . IDataReader . , -, Guid. , datareader 0 DBNull, 0 . , . - , ?

:

dataReader.GetInt("columnName1")
dataReader.GetString("columnName3")
dataReader.GetFloat("columnName3")

:

public static int? GetInt(this IDataReader r, string columnName)
{
    var i = r[columnName];      
    if (i.IsNull())
        return null; //or your preferred value

    return (int)i;
}

public static bool IsNull<T>(this T obj) where T : class
{
    return (object)obj == null || obj == DBNull.Value;
}

,

public static string GetString(this IDataReader r, string columnName)
{
}

public static float GetFloat(this IDataReader r, string columnName)
{
}

, .

public static T Get<T>(this IDataReader r, string columnName, T defaultValue = default(T))
{
    var obj = r[columnName];      
    if (obj.IsNull())
        return defaultValue;

    return (T)obj;
}


dataReader.Get<int>(1); //if DBNull should be treated as 0
dataReader.Get<int?>(1); //if DBNull should be treated as null
dataReader.Get<int>(1, -1); //if DBNull should be treated as a custom value, say -1

, , , . DBNull, ,

+4

.NET Framework 4.5

static class SqlReaderExtension
{
    public static async Task<T> ReadAsync<T>(this SqlDataReader reader, string fieldName)
    {
        if (reader == null) throw new ArgumentNullException(nameof(reader));
        if (string.IsNullOrEmpty(fieldName))
            throw new ArgumentException("Value cannot be null or empty.", nameof(fieldName));

        int idx = reader.GetOrdinal(fieldName);
        return await reader.GetFieldValueAsync<T>(idx);
    }
}


string result = await reader.ReadAsync<string>("FieldName");
0

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