What's the recommended way to start using types from a returned DataRow in C#?

Question

When looping through a DataRow and encountering types such as

DataRow dr;
dr["someString"]
dr["someInteger"]
dr["somedata"]

What's the best way to get them into their corresponding data types? dr["foo"] is just a generic object.

Also, are these able to be easily converted to nullable types? dr["someInteger"] could be null.

Answer 1

Simply casting the values to the right type should work:

(string) dr["someString"];
(int?) dr["someInteger"];
(byte[]) dr["somedata"];

Answer 2

If you can use .net 3.5, then you can use the Field extension method to more easily access the data if you know the type. An example would be:

 string somestring= row.Field<string>("SomeString");

Otherwise you're stuck with casting the field to the type of the object the old fashioned way.

Answer 3

When reading from a DataRow, your biggest enemy is a null value. In a DataRow, when a value is null, it is not equals to null: It is equals to DBNull.Value.

if(DBNull.Value == null)
{
   // Will never happen
}

Unless you know that your field cannot be null, it is not safe to cast. For example, the following example will fail if the data is DBNull:

string name = (string)dr["Name"];

If you can use the LINQ extensions, you can include the reference System.Data.DataSetExtensions and the namespace System.Data and call

string name = dr.Field<string>("Name");

If you cannot use LINQ, then you have to fall back to checking for null value with

string name = null;
if(!dr.IsNull("Name"))
    name = (string)dr["Name"];

Or you could code your own Field function like this:

public static T GetValue<T>(object value)
{
    if (value == null || value == DBNull.Value)
        return default(T);
    else
        return (T)value;
}

and get your value this way:

string name = GetValue<string>(dr["Name"]);

Answer 4

string GetString(DataRow dr, string ColumnName)
{
    if (dr.IsNull(ColumnName)) 
    {
        return null;
    }
    return (string)dr[ColumnName];
}

Answer 5

Another option is to use "as"

string str = dr["someString"] as string;

if it's DBNull.Value (or any other object not of type string), then str will get a real "null". Otherwise it will get the proper string value.

For value types, you can use nullable, i.e.

int? i = dr["someint"] as int?;

Again, it will get a real "null" instead of DBNull.Value. However, with nullable types you have to remember to use .Value, i.e.

int x = i.Value + 5;