[C#]IDataReader をちょっと使いやすくする

IDataReader を使うときそのままだとこんな感じだと思うんですが、

int intValue = (int) reader["int_field"];
string strValue = (string) reader["str_field"];
 

NULL のときとかちょっと面倒です。(なんで IDataReader.IsDBnull には IsDBNull(string name) みたいなオーバーロードがないんだろう

Nullable<int> nullableValue = null;
if (!reader.IsDBNull(reader.GetOrdinal("nullable_field")))
{
    nullableValue = (int) reader["nullable_field"];
}
 

なのでこんな風にできるようにしたい。

int intValue = reader.Field<int>("int_field");
string strValue = reader.Field<string>("str_field");
Nullable<int> nullableValue = reader.Field<Nullable<int>>("nullable_field");
int ifNullValue = reader.Field<int>("if_null_field", ifNull:-1);
 

3.5以上なら拡張メソッド作ればいいんですが... 残念ながら 2.0 な環境だったのでこんなヘルパクラスを作って実装しました。

	public class DataReaderHelper : IDataReader
	{
	public DataReaderHelper(IDataReader reader)
	{
	if (reader == null) throw new ArgumentNullException("reader");
	_reader = reader;
	}
	private readonly IDataReader _reader;
	public T Field<T>(string fieldName)
	{
	return Field<T>(_reader, fieldName, default(T), false);
	}
	public T Field<T>(string fieldName, T ifNull)
	{
	return Field<T>(_reader, fieldName, ifNull, true);
	}
	public bool IsDBNull(string fieldName)
	{
	return _reader.IsDBNull(_reader.GetOrdinal(fieldName));
	}
	private static T Field<T>(IDataReader reader, string fieldName, T ifNull, bool useIfNull)
	{
	Type type = typeof (T);
	Type valueType = Nullable.GetUnderlyingType(type);
	bool typeIsNullable = (valueType != null);
	if (!typeIsNullable)
	valueType = type;
	if (Convert.IsDBNull(reader[fieldName]))
	{
	if (typeIsNullable || !valueType.IsValueType || useIfNull)
	return ifNull;
	throw new InvalidCastException();
	}
	return (T)reader[fieldName];
	}
	public void Close()
	{
	_reader.Close();
	}
	public int Depth
	{
	get { return _reader.Depth; }
	}
	public DataTable GetSchemaTable()
	{
	return _reader.GetSchemaTable();
	}
	public bool IsClosed
	{
	get { return _reader.IsClosed; }
	}
	public bool NextResult()
	{
	return _reader.NextResult();
	}
	public bool Read()
	{
	return _reader.Read();
	}
	public int RecordsAffected
	{
	get { return _reader.RecordsAffected; }
	}
	public void Dispose()
	{
	_reader.Dispose();
	}
	public int FieldCount
	{
	get { return _reader.FieldCount; }
	}
	public bool GetBoolean(int i)
	{
	return _reader.GetBoolean(i);
	}
	public byte GetByte(int i)
	{
	return _reader.GetByte(i);
	}
	public long GetBytes(int i, long fieldOffset, byte[] buffer, int bufferoffset, int length)
	{
	return _reader.GetBytes(i, fieldOffset, buffer, bufferoffset, length);
	}
	public char GetChar(int i)
	{
	return _reader.GetChar(i);
	}
	public long GetChars(int i, long fieldoffset, char[] buffer, int bufferoffset, int length)
	{
	return _reader.GetChars(i, fieldoffset, buffer, bufferoffset, length);
	}
	public IDataReader GetData(int i)
	{
	return _reader.GetData(i);
	}
	public string GetDataTypeName(int i)
	{
	return _reader.GetDataTypeName(i);
	}
	public DateTime GetDateTime(int i)
	{
	return _reader.GetDateTime(i);
	}
	public decimal GetDecimal(int i)
	{
	return _reader.GetDecimal(i);
	}
	public double GetDouble(int i)
	{
	return _reader.GetDouble(i);
	}
	public Type GetFieldType(int i)
	{
	return _reader.GetFieldType(i);
	}
	public float GetFloat(int i)
	{
	return _reader.GetFloat(i);
	}
	public Guid GetGuid(int i)
	{
	return _reader.GetGuid(i);
	}
	public short GetInt16(int i)
	{
	return _reader.GetInt16(i);
	}
	public int GetInt32(int i)
	{
	return _reader.GetInt32(i);
	}
	public long GetInt64(int i)
	{
	return _reader.GetInt64(i);
	}
	public string GetName(int i)
	{
	return _reader.GetName(i);
	}
	public int GetOrdinal(string name)
	{
	return _reader.GetOrdinal(name);
	}
	public string GetString(int i)
	{
	return _reader.GetString(i);
	}
	public object GetValue(int i)
	{
	return _reader.GetValue(i);
	}
	public int GetValues(object[] values)
	{
	return _reader.GetValues(values);
	}
	public bool IsDBNull(int i)
	{
	return _reader.IsDBNull(i);
	}
	public object this[string name]
	{
	get { return _reader[name]; }
	}
	public object this[int i]
	{
	get { return _reader[i]; }
	}
	}

view raw DataReaderHelper.cs hosted with ❤ by GitHub

	DataReaderHelper reader = new DataReaderHelper(command.ExecuteReader());
	while (reader.Read())
	{
	int intValue = reader.Field<int>("int_field");
	string strValue = reader.Field<string>("str_field");
	Nullable<int> nullableValue = reader.Field<Nullable<int>>("nullable_field");
	int ifNullValue = reader.Field<int>("if_null_field", ifNull:-1);
	}

view raw UseCase.cs hosted with ❤ by GitHub

まあ実際は VB.NET なんですが... これで IDataReader が少し使いやすくなりました。