/// <summary>
/// Returns the item uniquely identified by <paramref name="id"/> from storage.
/// The class will remember its values, so we know how to deal with a later call to <see cref="SaveAsync(TId,TModel,System.Threading.CancellationToken)"/>.
/// </summary>
/// <returns>The found item or null.</returns>
public async Task <TModel> ReadAsync(TId id, CancellationToken cancellationToken = default)
{
var item = await _readService.ReadAsync(id, cancellationToken);
if (item == null)
{
return(null);
}
AddOrUpdateWithCopy(id, item, true);
return(item);
}
/// <summary>
/// Read and cache the item, but only if we have an aggressive caching strategy.
/// </summary>
/// <param name="id">The id of the item.</param>
/// <param name="service">A service to use for reading the item.</param>
/// <param name="token">Propagates notification that operations should be canceled</param>
protected async Task CacheMaybeSetAsync(TId id, IRead <TModel, TId> service, CancellationToken token = default(CancellationToken))
{
async Task <bool> IsAlreadyCachedAndGetIsOkToUpdate()
{
return(Options.DoGetToUpdate && await CacheItemExistsAsync(id, token));
}
var getAndSave = Options.SaveAll || await IsAlreadyCachedAndGetIsOkToUpdate();
if (!getAndSave)
{
return;
}
var item = await service.ReadAsync(id, token);
await CacheSetByIdAsync(id, item, token);
}
/// <summary>
/// If <paramref name="item"/> implements <see cref="IOptimisticConcurrencyControlByETag"/>
/// then the old value is read using <paramref name="service"/> and the values are verified to be equal.
/// The Etag of the item is then set to a new value.
/// </summary>
/// <param name="id"></param>
/// <param name="item"></param>
/// <param name="service"></param>
/// <param name="token">Propagates notification that operations should be canceled</param>
/// <returns></returns>
protected virtual async Task <TModel> MaybeVerifyEtagForUpdateAsync(TId id, TModel item, IRead <TModel, TId> service, CancellationToken token = default(CancellationToken))
{
var oldItem = await service.ReadAsync(id, token);
if (!(item is IOptimisticConcurrencyControlByETag etaggable))
{
return(oldItem);
}
if (Equals(oldItem, default(TModel)))
{
return(oldItem);
}
var oldEtag = (oldItem as IOptimisticConcurrencyControlByETag)?.Etag;
if (oldEtag?.ToLowerInvariant() != etaggable.Etag?.ToLowerInvariant())
{
throw new FulcrumConflictException($"The updated item ({item}) had an old ETag value.");
}
return(oldItem);
}
