[CAY-1508] Support for DataChannel filters

• Type: Task
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.1M1
• Fix Version/s: 3.1M2
• Component/s: Core Library
• Assignee: Andrus Adamchik
• Reporter: Andrus Adamchik
• Created: 14/Nov/10 03:29
• Updated: 14/Nov/10 09:54
• Resolved: 14/Nov/10 09:54

Description

Support for DataChannel filters with API similar to ServletFilters, only adapted for Cayenne (i.e. it will be mirroring DataChannel onQuery and onSync methods) :

public interface DataChannelFilter {

void init(DataChannel channel);

QueryResponse onQuery(
ObjectContext originatingContext,
Query query,
DataChannelFilterChain filterChain);

GraphDiff onSync(
ObjectContext originatingContext,
GraphDiff changes,
int syncType,
DataChannelFilterChain filterChain);
}

One difference with ServletFilter is the absence of "destroy" method in DataChannelFilter. Destroy is achieved via @BeforeScopeEnd annotation per filter.

DataChannelFilters may be good for tying multiple object lifecycle events together in one context, monitoring performance at the ObjectContext-level, and other good things.

TODO: One possible consequence of this feature is that channel decorators will provide no advantage as a design pattern, and relationships between ObjectContext and its parent DataChannel may not require such a high-level of abstraction (a leaky abstraction for that matter). E.g. we may get rid of DataDomainQuery, returning parent domain the old way via API calls.