Method WhereHasDescendant<TTarget>(Expression<Func<TTarget, bool>>, int?)

Filter by descendants: find objects that have a descendant of specified type matching condition.
Uses SQL operator $hasDescendant.
Supports polymorphic trees - can search for descendants of different type.

IRedbQueryable<TProps> WhereHasDescendant<TTarget>(Expression<Func<TTarget, bool>> descendantCondition, int? maxDepth = null) where TTarget : class