I find it difficult to understand the filtering with LLBLGen. In the attachment you will find the database structure of ReportRibbonItems - ReportsReportRibbonItems - Reports

I like to have all reports based on particular ReportRibbonItem where ReportsReportRibbonItemsEntity.IsActive = true

Now I have the following code without the extra filter: prefetchPath.Add(ReportRibbonItemsEntity.PrefetchPathReportsCollectionViaReportsReportRibbonItem, 0, null, null, sorter_local6)

Filtering is something and PrefetchPaths is completely a different thing.

Prefetchpaths are used to fetch related entities (a graph of connected entities) in one shot (precisely, one query for each entity type).

For filtering on related entities, as with plain SQL, you need to JOIN(use relations) then use predicates.

I need to extend the ReportRibbonItem with Reports collection via the N:N table ReportsReportRibbonItems. The prefetchpath does that for me.

The restriction: ReportsReportRibbonItemsEntity.IsActive = true I like to add to the prefetchpath: prefetchPath.Add(ReportRibbonItemsEntity.PrefetchPathReportsCollectionViaReportsReportRibbonItem, 0, null, null, sorter_local6)

The 3th and 4th parameter (additional filter / additional filter relation) should do this, but how ??

You have figured it out.

var additionalFilter = new PredicateExpression(ReportsReportRibbonItemsFields.IsActive == true);

var additionalFilterRelations = new RalationCollection();
additionalFilterRelations.Add(ReportsEntity.Relations.ReportsReportRibbonItemsEntity);

prefetchPath.Add(ReportRibbonItemsEntity.PrefetchPathReportsCollectionViaReportsReportRibbonItem, 0, additionalFilter, additionalFilterRelations, sorter_local6) 

Thanks