/// <summary>
/// Returns the only element of a sequence that satisfies a specified condition or
/// a default value if no such element exists; this method throws an exception if
/// more than one element satisfies the condition
/// </summary>
/// <typeparam name="TSource"></typeparam>
/// <param name="source">A sequence to return a single element from</param>
/// <param name="predicate">A function to test an element for a condition</param>
/// <returns>
/// The single element of the input sequence that satisfies the condition in predicate,
/// or default(TSource) if no such element is found
/// </returns>
public static Task <TSource> SingleOrDefaultAsync <TSource>(this IQueryable <TSource> source,
Expression <Func <TSource, bool> > predicate = null)
{
return(predicate == null?AsyncExtensions.SingleOrDefaultAsync(source) : AsyncExtensions.SingleOrDefaultAsync(source, predicate));
}
/// <summary>
/// Asynchronously loads first record from query.
/// Returns <c>default(TSource)</c>, if query doesn't return any records.
/// Throws exception, if query returns more than one record.
/// </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> SingleOrDefaultAsyncLinqToDB <TSource>(
this IQueryable <TSource> source,
CancellationToken token = default)
=> AsyncExtensions.SingleOrDefaultAsync(source.ToLinqToDB(), token);
/// <inheritdoc cref="AsyncExtensions.SingleOrDefaultAsync{TSource}(IQueryable{TSource}, Expression{Func{TSource, bool}}, CancellationToken)"/>
public static Task <TSource> SingleOrDefaultAsyncLinqToDB <TSource>(
this IQueryable <TSource> source,
Expression <Func <TSource, bool> > predicate,
CancellationToken token = default)
=> AsyncExtensions.SingleOrDefaultAsync(source.ToLinqToDB(), predicate, token);
