server: post category filter

server/szurubooru/search/configs/post_search_config.py

@@ -122,6 +122,34 @@ def _pool_filter(
     )(query, criterion, negated)
 
 
+def _category_filter(
+    query: SaQuery, criterion: Optional[criteria.BaseCriterion], negated: bool
+) -> SaQuery:
+    assert criterion
+
+    # Step 1. find the id for the category
+    q1 = db.session.query(model.TagCategory.tag_category_id).filter(
+        model.TagCategory.name == criterion.value
+    )
+
+    # Step 2. find the tags with that category
+    q2 = db.session.query(model.Tag.tag_id).filter(
+        model.Tag.category_id.in_(q1)
+    )
+
+    # Step 3. find all posts that have at least one of those tags
+    q3 = db.session.query(model.PostTag.post_id).filter(
+        model.PostTag.tag_id.in_(q2)
+    )
+
+    # Step 4. profit
+    expr = model.Post.post_id.in_(q3)
+    if negated:
+        expr = ~expr
+
+    return query.filter(expr)
+
+
 class PostSearchConfig(BaseSearchConfig):
     def __init__(self) -> None:
         self.user = None  # type: Optional[model.User]
@@ -349,6 +377,7 @@ def named_filters(self) -> Dict[str, Filter]:
                     ),
                 ),
                 (["pool"], _pool_filter),
+                (["category"], _category_filter),
             ]
         )