/// <summary>
/// Executes query and projects each record into a new form.
/// </summary>
/// <typeparam name="T">Type of the output collection.</typeparam>
/// <param name="select">Source <see cref="Select"/> to read data.</param>
/// <param name="readMethod">Record transformation method.</param>
/// <returns>
/// An <see cref="IEnumerable{T}"/> whose elements are the result of invoking the transform
/// function on each line read.
/// </returns>
public static IEnumerable <T> ExecuteEnumerable <T>(this Select select,
ExecuteReaderTypedReadMethod <T> readMethod)
{
using (DBExecutor dbExecutor = EnsureSpecialDbExecutor(select.UserConnection, select.QueryKind)) {
using (IDataReader dataReader = select.ExecuteReader(dbExecutor)) {
while (dataReader.Read())
{
yield return(readMethod(dataReader));
}
}
}
}
/// <summary>
/// Reads single record and applies transformation on it.
/// </summary>
/// <typeparam name="T">Type of the output item.</typeparam>
/// <param name="select">Source <see cref="Select"/> to read data.</param>
/// <param name="readMethod">Record transformation method.</param>
/// <param name="item">Read and transformed item, or default <see cref="T"/> if nothing was read.</param>
/// <returns>Returns <c>true</c> if record was read, <c>false</c> otherwise.</returns>
/// <example>
/// This sample shows how to call the <see cref="ExecuteSingleRecord{T}"/> method.
/// <code>
/// select.ExecuteSingleRecord(reader => new {
/// Id = reader.GetColumnValue<Guid>("Id"),
/// Name = reader.GetColumnValue<string>("Name")
/// }, out var item);
/// </code>
/// </example>
public static bool ExecuteSingleRecord <T>(this Select select,
ExecuteReaderTypedReadMethod <T> readMethod, out T item)
{
using (DBExecutor dbExecutor = EnsureSpecialDbExecutor(select.UserConnection, select.QueryKind)) {
using (IDataReader dataReader = select.ExecuteReader(dbExecutor)) {
if (dataReader.Read())
{
item = readMethod(dataReader);
return(true);
}
item = default(T);
return(false);
}
}
}
