Будьте в спящем режиме JPA и Spring javax.persistence. TransactionRequiredException: никакая транзакция не происходит

Демонстрация красоты LINQ путем написания метода расширения.

/// <summary>
/// Gets the duration of the set union of the specified intervals.
/// </summary>
/// <param name="timeLapses">Sequence of <see cref="TimeLapse"/> ordered by <see cref="TimeLapse.StartTime"/>.</param>
public static TimeSpan UnionDurations(this IEnumerable<TimeLapse> timeLapses)
{
    using (var e = timeLapses.GetEnumerator())
    {
        if (!e.MoveNext()) // no items, no duration
            return TimeSpan.Zero;

        var prev = e.Current;
        var total = prev.EndTime - prev.StartTime; // set running total to duration of 1st interval

        while (e.MoveNext())
        {
            var curr = e.Current;
            if (curr.StartTime < prev.StartTime) throw new Exception($"{nameof(timeLapses)} are not in ascending {nameof(TimeLapse.StartTime)} order.");

            var increase = curr.EndTime - (curr.StartTime > prev.EndTime ? curr.StartTime : prev.EndTime);
            if (increase <= TimeSpan.Zero) continue;
            total += increase;
            prev = curr;
        }

        return total;
    }
}

Тестовый код:

var input = new Dictionary<string, IList<TimeLapse>>
{
    {
        "A",
        new[]
        {
            new TimeLapse{ StartTime = new DateTime(2019, 1, 17, 0, 0, 0), EndTime = new DateTime(2019, 1, 17, 3, 0, 0)},
            new TimeLapse{ StartTime = new DateTime(2019, 1, 17, 1, 0, 0), EndTime = new DateTime(2019, 1, 17, 2, 0, 0)},
            new TimeLapse{ StartTime = new DateTime(2019, 1, 17, 1, 0, 0), EndTime = new DateTime(2019, 1, 17, 4, 0, 0)},
            new TimeLapse{ StartTime = new DateTime(2019, 1, 17, 5, 0, 0), EndTime = new DateTime(2019, 1, 17, 7, 0, 0)}
        }
    },
    {
        "B",
        new TimeLapse [0]
    }
};
var result = input
    .Select(kv => new
    {
        Device = kv.Key,
        FaultyDuration = kv.Value
            // .OrderBy(tl => tl.StartTime) // this line can be removed if already ordered by StartTime
            .UnionDurations()
    })
    .ToList();
// { Device = A, FaultyDuration = 06:00:00 }
// { Device = B, FaultyDuration = 00:00:00 }