public async Task SaveAsync(AggregateRoot aggregate)
{
Logger.Log($"Preparing to save aggregate {aggregate.Id} to DynamoDB");
var uncommittedChanges = aggregate.GetUncommittedChanges();
var version = aggregate.Version;
foreach (var @event in uncommittedChanges)
{
@event.Version = ++version;
@event.Timestamp = DateTime.UtcNow;
// Write event to DynamoDB
try
{
var eventTable = Table.LoadTable(_dynamoDbClient, _tableName);
var record = new Document();
var prop = @event.GetType().GetMembers().Where(m => m.MemberType == MemberTypes.Property).ToList();
foreach (var p in prop)
{
var name = p.Name;
// There should only be 4 fields in an Event - Id, Version, EventName, and Event
if (p.Name != nameof(Event.Id) && p.Name != nameof(Event.Version) && p.Name != nameof(Event.EventName))
{
name = nameof(Event);
record[name] = JsonConvert.SerializeObject(@event);
}
else
{
record[name] = JsonConvert.SerializeObject(@event.GetType().GetProperty(name).GetValue(@event, null));
}
}
Logger.Log($"Saving aggregate to DynamoDB");
await eventTable.PutItemAsync(record);
Logger.Log($"Successfully saved aggregate to DynamoDB");
}
catch (Exception ex)
{
// TODO Surface exception up
Logger.Log($"ERROR: {ex.Message}");
throw new Exception(ex.Message);
}
Logger.Log($"Checking if snapshots should be saved: {version > 2 && version % 3 == 0}");
// Save a snapshot every 3 events
if (version > 2 && version % 3 == 0)
{
var originator = (ISnapshot)aggregate;
var snapshot = originator.GetSnapshot();
snapshot.Timestamp = DateTime.UtcNow;
await SaveSnapshotAsync(snapshot);
}
}
}
private async Task <QueryResponse> GetByIdAsync(Guid id)
{
Logger.Log($"Scanning DynamoDB for aggregate: {id}");
// Read events from DynamoDB
var request = new QueryRequest
{
TableName = _tableName,
KeyConditionExpression = "Id = :v_Id and Version > :v_Version",
ExpressionAttributeValues = new Dictionary <string, AttributeValue> {
{ ":v_Id", new AttributeValue {
S = $"\"{id.ToString()}\""
} },
{ ":v_Version", new AttributeValue {
S = "0"
} }
}
};
var response = await _dynamoDbClient.QueryAsync(request);
Logger.Log($"Found items: {response.Items.Count}");
return(response);
}
public async Task SaveSnapshotAsync(Snapshot snapshot)
{
try
{
var eventTable = Table.LoadTable(_dynamoDbClient, _tableName);
var record = new Document
{
["Id"] = JsonConvert.SerializeObject(snapshot.Id),
["Version"] = "Snapshot-" + (snapshot.Version + 1),
["Event"] = JsonConvert.SerializeObject(snapshot),
["EventName"] = "Snapshot"
};
Logger.Log("Saving snapshot to DynamoDB");
await eventTable.PutItemAsync(record);
Logger.Log("Successfully saved snapshot to DynamoDB");
}
catch (Exception ex)
{
// TODO Surface exception up
Logger.Log($"ERROR: {ex.Message}");
throw new Exception(ex.Message);
}
}
// TODO Get up to most recent snapshot and any newer events only
private IEnumerable <Event> GetEventsFromDynamoDbResponse(IEnumerable <Dictionary <string, AttributeValue> > items)
{
var events = new List <Event>();
Logger.Log($"Getting events from {items.Count()} items");
foreach (var item in items)
{
var eventType = item.FirstOrDefault(i => i.Key == nameof(Event.EventName)).Value.S.Trim('"');
Logger.Log($"Item EventType: {eventType}");
var type = AppDomain.CurrentDomain.GetAssemblies().SelectMany(x => x.GetTypes()).First(x => x.Name == eventType);
Logger.Log($"Item Type: {type}");
if (type == typeof(Snapshot))
{
continue;
}
var @event = JsonConvert.DeserializeObject(item.FirstOrDefault(i => i.Key == nameof(Event)).Value.S, type);
Logger.Log($"Item Event: {@event}");
events.Add((Event)@event);
}
return(events);
}
private async Task CreateDynamoDbTableAsync(string tableName)
{
var response = new CreateTableResponse();
try
{
var request = new CreateTableRequest
{
TableName = tableName,
AttributeDefinitions = new List <AttributeDefinition>
{
new AttributeDefinition
{
AttributeName = "Id",
AttributeType = "S"
},
new AttributeDefinition
{
AttributeName = "Version",
AttributeType = "S"
}
},
KeySchema = new List <KeySchemaElement>
{
new KeySchemaElement {
AttributeName = "Id", KeyType = KeyType.HASH
},
new KeySchemaElement {
AttributeName = "Version", KeyType = KeyType.RANGE
}
},
ProvisionedThroughput = new ProvisionedThroughput
{
ReadCapacityUnits = 5,
WriteCapacityUnits = 5
},
StreamSpecification = new StreamSpecification
{
StreamViewType = StreamViewType.NEW_IMAGE,
StreamEnabled = true
}
};
var createTableResponse = _dynamoDbClient.CreateTableAsync(request);
response = await createTableResponse;
}
catch (Exception ex)
{
Logger.Log($"ERROR: Failed to create the new table, because: {ex.Message}");
}
await WaitTillTableCreatedAsync(tableName, response);
}
private async Task DeleteDynamoDbTableAsync(string tableName)
{
var response = new DeleteTableResponse();
try
{
var deleteResponse = _dynamoDbClient.DeleteTableAsync(tableName);
response = await deleteResponse;
}
catch (Exception ex)
{
Logger.Log($"ERROR: Failed to delete the table, because:\n {ex.Message}");
}
await WaitTillTableDeletedAsync(tableName, response);
}