/// <summary>Decrements the count of an (index, value) pair in the multimap, and optionally removes it if the count reaches zero.</summary>
/// <param name="trans">Transaction used for the operation</param>
/// <param name="key">Key of the entry</param>
/// <param name="value">Value for the <paramref name="key"/> to decrement</param>
/// <remarks>If the updated count reaches zero or less, and AllowNegativeValues is not set, the key will be cleared from the map.</remarks>
public async Task SubtractAsync([NotNull] IFdbTransaction trans, TKey key, TValue value)
{
if (trans == null)
{
throw new ArgumentNullException(nameof(trans));
}
Slice k = this.Subspace.Keys[key, value];
if (this.AllowNegativeValues)
{
trans.AtomicDecrement64(k);
// note: it's faster, but we will end up with counts less than or equal to 0
// If 'k' does not already exist, its count will be set to -1
}
else
{
Slice v = await trans.GetAsync(k).ConfigureAwait(false);
if (this.AllowNegativeValues || v.ToInt64() > 1) //note: Slice.Nil.ToInt64() will return 0
{
trans.AtomicDecrement64(k);
//note: since we already read 'k', the AtomicAdd will be optimized into the equivalent of Set(k, v - 1) by the client, unless RYW has been disabled on the transaction
//TODO: if AtomicMax ever gets implemented, we could use it to truncate the values to 0
}
else
{
trans.Clear(k);
}
}
}
/// <summary>Decrements the count of an (index, value) pair in the multimap, and optionally removes it if the count reaches zero.</summary>
/// <param name="trans">Transaction used for the operation</param>
/// <param name="key">Key of the entry</param>
/// <param name="value">Value for the <paramref name="key"/> to decrement</param>
/// <remarks>If the updated count reaches zero or less, and AllowNegativeValues is not set, the key will be cleared from the map.</remarks>
public void Subtract(IFdbTransaction trans, TKey key, TValue value)
{
if (trans == null)
{
throw new ArgumentNullException(nameof(trans));
}
// decrement, and optionally clear the key if it reaches zero
trans.AtomicDecrement64(this.Subspace[key, value], clearIfZero: !this.AllowNegativeValues);
}