/// <summary>
/// Asynchronously loads first record from query.
/// Throws exception, 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.</returns>
public static Task <TSource> FirstAsyncLinqToDB <TSource>(
this IQueryable <TSource> source,
CancellationToken token = default)
=> AsyncExtensions.FirstAsync(source.ToLinqToDB(), token);
/// <summary>
/// Asynchronously loads first record from query, filtered using provided predicate.
/// Throws exception, 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.</returns>
public static Task <TSource> FirstAsyncLinqToDB <TSource>(
this IQueryable <TSource> source,
Expression <Func <TSource, bool> > predicate,
CancellationToken token = default)
=> AsyncExtensions.FirstAsync(source.ToLinqToDB(), predicate, token);
/// <summary>
/// Returns the first element of a sequence that satisfies a specified condition
/// </summary>
/// <typeparam name="TSource"></typeparam>
/// <param name="source">An sequence to return an element from</param>
/// <param name="predicate">A function to test each element for a condition</param>
/// <returns>The first element in source that passes the test in predicate</returns>
public static Task <TSource> FirstAsync <TSource>(this IQueryable <TSource> source,
Expression <Func <TSource, bool> > predicate = null)
{
return(predicate == null?AsyncExtensions.FirstAsync(source) : AsyncExtensions.FirstAsync(source, predicate));
}