/// <summary>
/// Executes the query, and returns the first column of the first row in the result set returned by the query.
/// Additional columns or rows are ignored.
/// </summary>
/// <typeparam name="T">Type of model.</typeparam>
/// <param name="query">The query.</param>
/// <returns>
/// The first column of the first row in the result set, or <see langword="null"/> if the result set is empty.
/// Returns a maximum of 2033 characters.
/// </returns>
/// <exception cref="ArgumentNullException">If query is null.</exception>
public object ExecuteScalar <T>(IQuery <T> query)
{
Check.NotNull(query, nameof(query));
using (var cnHelper = OpenConnection())
using (DbCommandInfo commandInfo = CreateCommand(query.Expression))
{
_logger.LogCommand(commandInfo.Command);
if (commandInfo.Reader == null)
{
return(commandInfo.Command.ExecuteScalar());
}
else
{
using (IDataReaderEnvelope reader = commandInfo.Reader)
{
reader.SetInnerReader(commandInfo.Command.ExecuteReader());
if (reader.Read())
{
return(reader.GetValue(0));
}
}
}
return(null);
}
}
public QueryDataReader(IDbCommand command, IDataReaderEnvelope readerEnvelope, bool closeConnectionWhenFinished)
{
Check.NotNull(command, nameof(command));
_command = command;
if (readerEnvelope == null)
{
_reader = _command.ExecuteReader();
}
else
{
readerEnvelope.SetInnerReader(_command.ExecuteReader());
_reader = readerEnvelope;
}
_closeConnectionWhenFinished = closeConnectionWhenFinished;
}
public DbCommandInfo(DbCommand command, IDataReaderEnvelope reader)
{
Command = command;
Reader = reader;
}
/// <summary>
/// Creates an instance with specified <paramref name="query"/> and <paramref name="reader"/>.
/// </summary>
/// <param name="query">SQL query.</param>
/// <param name="reader">Reader used for query, if database engine itself cannot handle query itself.</param>
public QueryInfo(string query, IDataReaderEnvelope reader)
{
Query = query;
Reader = reader;
}
