NHibernate Change Auditing and Components - nhibernate

Question

An integral part of our architecture as our system must provide a dashboard for users to explicitly publish data changes from environment to another. We looked at NH Evers, but we needed to many domain specific things to be baked into the architecture. We've been successfully using NHibernate's eventing model to track and log state changes (to another table) in our system, but recently stumbled across a snag with Components. When IPostInsertEventListener and IPostUpdateEventListener is fired it publishes a value arrays that denote the current state of the entity. In the case of updates, it publishes an array denoting previous state as well. We are using these arrays to save off "before" and "after" state into our table. When the property is a Component, the actual value (item in the area) is the component instance itself - i.e. an untyped complex object. Short of cross referencing the metamodel mapper and reflecting on that to pull out the individual values, how can I get at the actual values that make up the component? I'm able to get at the column names that map to the Component's members, but not the before and after values.
I've been digging through the NH source, and I'm not finding how to pull out these values, but obviously NH knows how to do this internally as it's able to publish the sql properly. Here's a modified/verbose version of the code I currently have that highlights the issue:
public static RowChangedReport Load(IChangeTrackable trackable, object entityId, AbstractEntityPersister persister, object[] state, object[] oldState)
{
var report = new RowChangedReport
{
Entity = trackable,
EntityTypeFullName = persister.EntityName,
TableName = new TableName(persister.GetTableName()),
EntityId = entityId,
};
var authContext = AuthenticationContext.Current;
if (authContext != null)
report.SecurityContextUserId = authContext.UserId;
if (persister.PropertyNames != null && state != null)
{
report.ChangedType = oldState == null ? RowChangedTypes.New : RowChangedTypes.Modified;
for (var index = 0; index < persister.PropertyNames.Length; index++)
{
var propertyName = persister.PropertyNames[index];
IType propertyType = persister.PropertyTypes[index];
if (!propertyType.IsCollectionType)
{
AddColumnChangeReport(persister, state, oldState, index, propertyName, report);
}
}
}
report.FinalizeState();
return report;
}
private static void AddColumnChangeReport(AbstractEntityPersister persister, object[] state, object[] oldState, int index, string propertyName, RowChangedReport report)
{
var currentValue = state[index];
// for simple properties, this is always a single element array
// for components, this is an array with an element for each member on the component - i.e. how the component is mapped
string[] columns = persister.GetPropertyColumnNames(propertyName);
var previousValue = oldState == null ? null : oldState[index];
if (!Equals(currentValue, previousValue))
{
if (report.ChangedType == RowChangedTypes.Modified && propertyName == IsActivePropertyName)
report.FlagAsDeleted();
foreach (var column in columns)
{
// if this is a component, both the currentValue and the previousValue are complex objects
// need to have a way to get the actual member value per column!
report.AddChange(new ColumnChangedReport(report, propertyName, column, previousValue, currentValue));
}
}
}

Answer 1

OK, after a few hours reading the NH code, I stumbled across Tuplizers and tracked them back to the property Type. So the solution is pretty simple - for components, you need to detect them as such, cast to the ComponentType Type and then ask ComponentType for the property values. Here some code that's working for me:
public static RowChangedReport Load(IChangeTrackable trackable, object entityId, AbstractEntityPersister persister, object[] state, object[] oldState)
{
var report = new RowChangedReport
{
Entity = trackable,
EntityTypeFullName = persister.EntityName,
TableName = new TableName(persister.GetTableName()),
EntityId = entityId,
};
var authContext = AuthenticationContext.Current;
if (authContext != null)
report.SecurityContextUserId = authContext.UserId;
if (persister.PropertyNames != null && state != null)
{
report.ChangedType = oldState == null ? RowChangedTypes.New : RowChangedTypes.Modified;
for (var index = 0; index < persister.PropertyNames.Length; index++)
{
var propertyName = persister.PropertyNames[index];
IType propertyType = persister.PropertyTypes[index];
if (!propertyType.IsCollectionType)
{
AddColumnChangeReport(persister, state, oldState, index, propertyName, propertyType, report);
}
}
}
report.FinalizeState();
return report;
}
private static void AddColumnChangeReport(AbstractEntityPersister persister, object[] state, object[] oldState, int index, string propertyName, IType propertyType, RowChangedReport report)
{
var currentValue = state[index];
string[] columns = persister.GetPropertyColumnNames(propertyName);
var previousValue = oldState == null ? null : oldState[index];
if (!Equals(currentValue, previousValue))
{
if (report.ChangedType == RowChangedTypes.Modified && propertyName == IsActivePropertyName)
report.FlagAsDeleted();
if (propertyType.IsComponentType)
{
ComponentType component = (ComponentType)propertyType;
object[] componentCurrentValues = null;
if (currentValue != null)
componentCurrentValues = component.GetPropertyValues(currentValue, EntityMode.Poco);
object[] componentPreviousValues = null;
if (currentValue != null)
componentPreviousValues = component.GetPropertyValues(previousValue, EntityMode.Poco);
if ((componentCurrentValues != null && componentCurrentValues.Length != columns.Length) ||
(componentPreviousValues != null && componentPreviousValues.Length != columns.Length))
throw new ConventionViolationException(GetComponentArraysExceptionMessage(persister, propertyName, columns, componentPreviousValues, componentCurrentValues));
for (int i = 0; i < columns.Length; i++)
{
var column = columns[i];
var componentPreviousValue = componentPreviousValues == null ? null : componentPreviousValues[i];
var componentCurrnetValue = componentCurrentValues == null ? null : componentCurrentValues[i];
report.AddChange(new ColumnChangedReport(report, propertyName, column, componentPreviousValue, componentCurrnetValue));
}
}
else
{
if (columns.Length > 1)
throw new ConventionViolationException("Expected only component properties to have multiple columns. Property '{0}' on entity {1} is violating that assumption.".FormatWith(propertyName, persister.EntityName));
report.AddChange(new ColumnChangedReport(report, propertyName, columns[0], previousValue, currentValue));
}
}
}