OleDbParameterCollection has no constructor defined

Question

In my project, I have a DBAdapter class that deals with database queries.

public class DBAdapter
{
    private OleDbConnection _connection;

    private void _Connect()
    {
        this._connection = new OleDbConnection();
        _connection.ConnectionString = ConfigurationManager.AppSettings["Accessconnection"];
        _connection.Open();
    }

    private void _Disconnect()
    {
        _connection.Close();
    }


    public DataTable Select(string query, OleDbParameterCollection parameters = null)
    {

        OleDbCommand cmd = new OleDbCommand();
        OleDbDataAdapter dataAdapter = new OleDbDataAdapter();
        DataSet dataSet = new DataSet();
        DataTable dataTable = new DataTable();
        query = "SELECT " + query;

        if (parameters != null)
        {
            foreach (OleDbParameter parameter in parameters)
            {
                cmd.Parameters.Add(parameter);
            }
        }

        this._Connect();
        cmd.Connection = _connection;
        cmd.CommandText = query;

        if (parameters != null)  {
            cmd.Prepare();
        }
        dataAdapter.SelectCommand = cmd;
        dataAdapter.Fill(dataSet, "results");
        this._Disconnect();

        dataTable = dataSet.Tables["results"];
        return dataTable;
    }

}

In order to perform prepared queries, the Select method has an optionnal OleDBParameterCollection parameter. Then, I have multiple Mappers for each domain object in my project, for example UserMapper, that use DataAdapter class to run queries (for example find user by id).

    public class UserMapper : DataMapperAbstract
        {

            public User findByID(int id)
            {
                User user = new User()
                string query = "* FROM USER WHERE idUser = ?";
                OleDbParameterCollection parameters = new OleDbParameterCollection();
                parameters.Add(new OleDbParameter("idUser", OleDbType.Integer).Value = id);

                // Prepared query
                DataTable results = adapter.Select(query, parameters);
                this._populateData(user, results.Rows[0]);
                return user;
            }
    }

Unfortunately, I have an error at this line

   OleDbParameterCollection parameters = new OleDbParameterCollection();

VS says that the type OleDbParameterCollection has no constructor defined, and I don't really understand what is the problem here. Maybe I don't have rights to instantiate OleDbParameterCollection, but in that case, how should I pass a collection of parameters to my DBAdapter's method ?

Answer 1

OleDbParameterCollection doesn't expose public constructor we can access. It doesn't meant to be used that way so, simply change your method parameter to accept list of OleDbParameter instead of OleDbParameterCollection :

public DataTable Select(string query, List<OleDbParameter> parameters = null)
{
}

Then use it accordingly :

List<OleDbParameter> parameters = new List<OleDbParameter>();
parameters.Add(new OleDbParameter("idUser", OleDbType.Integer){ Value = id });

// Prepared query
DataTable results = adapter.Select(query, parameters);

Answer 2

OleDbParameterCollection has no public constructors.

When the OleDbDataAdapter object is instantiated it automatically creates an OleDbParameterCollection object for you within the SelectCommand object.

Here is some code from MSDN that I found:

OleDbDataAdapter adapter =
new OleDbDataAdapter(queryString, connection);
// Set the parameters.
adapter.SelectCommand.Parameters.Add(
        "@CategoryName", OleDbType.VarChar, 80).Value = "toasters";

Here is the link: http://msdn.microsoft.com/en-us/library/system.data.oledb.oledbparametercollection(v=vs.110).aspx

You may need to modify the way you run the query a little bit. But, it looks like you've already got an adapter object in there, so it shouldn't be too hard.