Don't treat isNull as a constant (#708)

server/src/instant/db/datalog.clj

@@ -95,8 +95,6 @@
 (def variable? (fn [x]
                  (and (symbol? x) (not= x '_))))
 
-(def constant? (comp not symbol?))
-
 (def named-variable? (partial uspec/tagged-as? :variable))
 (def named-constant? (partial uspec/tagged-as? :constant))
 

server/src/instant/db/instaql.clj

@@ -183,14 +183,15 @@
                             (grow-paths path)))})
 
         (and (map? v) (contains? v :$isNull) (= true (:$isNull v)))
-        ;; If the where cond has `$isNull=true`, then we
-        ;; need it should match if any of the intermediate
-        ;; paths are null
-        (let [path (string/split (name k) #"\.")]
-          {:or (concat [[[path v]]]
-                       (map (fn [p]
-                              [[p {:$isNull true}]])
-                            (grow-paths path)))})
+        ;; If the where cond has `$isNull=true`, then we need it to
+        ;; match if any of the intermediate paths are null
+        (let [path (string/split (name k) #"\.")
+              conds (map (fn [p]
+                           [[p {:$isNull true}]])
+                         (grow-paths path))]
+          (if (= 1 (count conds))
+            {:and conds}
+            {:or conds}))
 
         :else [(string/split (name k) #"\.") v]))
 
@@ -568,7 +569,7 @@
    [?e attr-id 5] => 5
    [5 attr-id ?v] => 5"
   [[e _ v :as _attr-pat]]
-  (some d/constant? [e v]))
+  (some attr-pat/constant-component? [e v]))
 
 (defn- optimize-attr-pats
   "Given a list of attr pats, this tries to return a list that will be more

server/src/instant/db/model/attr_pat.clj

@@ -48,6 +48,10 @@
                 )]
     (if v-actualized? v-idx e-idx)))
 
+(defn constant-component? [component]
+  (and (not (symbol? component))
+       (not (:$isNull component))))
+
 (defn component-actualized?
   "A component is actualized if:
    a. It is a constant
@@ -57,7 +61,7 @@
     [?bookshelves books-attr ?books]] ;; ?bookshelves is actualized (it's been bound)
   "
   [seen component]
-  (or (d/constant? component)
+  (or (constant-component? component)
       (seen component)))
 
 (defn attr-by-id