/// <summary>
/// Asynchronously loads first record from query.
/// Returns <c>default(TSource)</c>, if query doesn't return any records.
/// </summary>
/// <typeparam name="TSource">Query element type.</typeparam>
/// <param name="source">Source query.</param>
/// <param name="token">Optional asynchronous operation cancellation token.</param>
/// <returns>First record from query results or <c>default(TSource)</c> for empty resultset.</returns>
public static Task <TSource> FirstOrDefaultAsyncLinqToDB <TSource>(
this IQueryable <TSource> source,
CancellationToken token = default)
=> AsyncExtensions.FirstOrDefaultAsync(source.ToLinqToDB(), token);
/// <summary>
/// Asynchronously loads first record from query, filtered using provided predicate.
/// Returns <c>default(TSource)</c>, if query doesn't return any records.
/// </summary>
/// <typeparam name="TSource">Query element type.</typeparam>
/// <param name="source">Source query.</param>
/// <param name="predicate">Query filter predicate.</param>
/// <param name="token">Optional asynchronous operation cancellation token.</param>
/// <returns>First record from query results or <c>default(TSource)</c> for empty resultset.</returns>
public static Task <TSource> FirstOrDefaultAsyncLinqToDB <TSource>(
this IQueryable <TSource> source,
Expression <Func <TSource, bool> > predicate,
CancellationToken token = default)
=> AsyncExtensions.FirstOrDefaultAsync(source.ToLinqToDB(), predicate, token);
/// <summary>
/// Returns the first element of a sequence, or a default value if the sequence contains no elements
/// </summary>
/// <typeparam name="TSource">The type of the elements of source</typeparam>
/// <param name="source">Source</param>
/// <param name="predicate">Predicate</param>
/// <returns>default(TSource) if source is empty; otherwise, the first element in source</returns>
public static Task <TSource> FirstOrDefaultAsync <TSource>(this IQueryable <TSource> source,
Expression <Func <TSource, bool> > predicate = null)
{
return(predicate == null?AsyncExtensions.FirstOrDefaultAsync(source) : AsyncExtensions.FirstOrDefaultAsync(source, predicate));
}