+ /**
+ * Scope a query to find items where the the child has the given childSlug
+ * where its parent has the bookSlug.
+ */
+ public function scopeWhereSlugs(Builder $query, string $bookSlug, string $childSlug)
+ {
+ return $query->with('book')
+ ->whereHas('book', function (Builder $query) use ($bookSlug) {
+ $query->where('slug', '=', $bookSlug);
+ })
+ ->where('slug', '=', $childSlug);
+ }
+