/// <summary>
/// Append the event to the end of the event stream
/// </summary>
/// <param name="eventInstance">
/// The event to append to the end of the event stream
/// </param>
/// <param name="expectedTopSequenceNumber">
/// if this is set to > 0 and the event stream is further on then a consistency issue has arisen and the
/// event should not be written but rather throw an error
/// </param>
/// <param name="eventVersionNumber">
/// The version number to add to the event wrapper
/// </param>
/// <param name="streamConstraint">
/// An additional constrain that must be satisfied by the event stream in order to persist the event
/// </param>
/// <returns></returns>
public async Task <IAppendResult> AppendEvent(IEvent eventInstance,
int expectedTopSequenceNumber = 0,
int eventVersionNumber = 1,
EventStreamExistenceConstraint streamConstraint = EventStreamExistenceConstraint.Loose)
{
if (base.EventStreamBlob != null)
{
// acquire a lease for the blob..
string writeStreamLeaseId = null;
if (await Exists())
{
writeStreamLeaseId = await base.EventStreamBlob.AcquireLeaseAsync(TimeSpan.FromSeconds(15));
}
int nextSequence = await base.GetSequenceNumber() + 1;
if (expectedTopSequenceNumber > 0)
{
// check against actual top sequence number
if ((expectedTopSequenceNumber + 1) < nextSequence)
{
throw new EventStreamWriteException(this,
(nextSequence - 1),
message: $"Out of sequence write - expected seqeunce number {expectedTopSequenceNumber }",
source: "Blob Event Stream Writer");
}
}
string eventName = "";
if (null != eventInstance)
{
eventName = EventNameAttribute.GetEventName(eventInstance.GetType());
}
// create an access condition
AccessCondition condition = AccessCondition.GenerateEmptyCondition();
if (streamConstraint == EventStreamExistenceConstraint.MustBeNew)
{
condition = AccessCondition.GenerateIfNotExistsCondition();
}
if (streamConstraint == EventStreamExistenceConstraint.MustExist)
{
condition = AccessCondition.GenerateIfExistsCondition();
}
if (!string.IsNullOrWhiteSpace(writeStreamLeaseId))
{
condition.LeaseId = writeStreamLeaseId;
}
// default the writer context if it is not already set
if (null == _writerContext)
{
_writerContext = WriteContext.DefaultWriterContext();
}
BlobBlockJsonWrappedEvent evtToWrite = BlobBlockJsonWrappedEvent.Create(eventName,
nextSequence,
eventVersionNumber,
null,
eventInstance,
_writerContext);
try
{
// Create it if it doesn't exist and initialsie the metadata
await base.Refresh();
Microsoft.Azure.Storage.OperationContext context = new Microsoft.Azure.Storage.OperationContext()
{
};
await EventStreamBlob.AppendBlockAsync(new System.IO.MemoryStream(Encoding.UTF8.GetBytes(evtToWrite.ToJSonText())),
"",
condition,
null, // use the default blob request options
context
);
}
catch (Microsoft.Azure.Storage.StorageException exBlob)
{
throw new EventStreamWriteException(this,
(nextSequence - 1),
message: "Failed to save an event to the event stream",
source: "Blob Event Stream Writer",
innerException: exBlob);
}
await IncrementSequence(writeStreamLeaseId);
if (!string.IsNullOrWhiteSpace(writeStreamLeaseId))
{
// and release the lease
await base.EventStreamBlob.ReleaseLeaseAsync(condition);
}
int sequence = await base.GetSequenceNumber();
return(new AppendResult((sequence == 0), sequence));
}
else
{
return(null);
}
}