Fixed a bug when fn inside a query on empty relation returned non-emp…

…ty result

CHANGELOG.md

@@ -4,6 +4,7 @@
 - `(datascript/datom e a v & [tx added])` call for creating new datoms
 - Added missing aggregate funs: `avg`, `median`, `variance`, `stddev` and `count-distinct` (issue #42, thx [@montyxcantsin](https://github.com/montyxcantsin))
 - `min` and `max` aggregates use comparator instead of default js `<` comparison
+- Fixed a bug when fn inside a query on empty relation returned non-empty result
 
 # 0.6.0
 

src/datascript/query.cljs

@@ -181,19 +181,26 @@
 
 ;;
 
-(defn in->rel [form value]
-  (condp looks-like? form
-    '[_ ...] ;; collection binding [?x ...]
-      (reduce sum-rel
-        (map #(in->rel (first form) %) value))
-    '[[*]]   ;; relation binding [[?a ?b]]
-      (reduce sum-rel
-        (map #(in->rel (first form) %) value))
-    '[*]     ;; tuple binding [?a ?b]
-      (reduce prod-rel
-        (map #(in->rel %1 %2) form value))
-    '_       ;; regular binding ?x
-      (Relation. {form 0} [#js [value]])))
+(defn in->rel
+  ([form]
+    (let [attrs (as-> form form
+                  (flatten form)
+                  (filter #(and (symbol? %) (not= '... %) (not= '_ %)) form)
+                  (zipmap form (range)))]
+      (Relation. attrs ())))
+  ([form value]
+    (condp looks-like? form
+      '[_ ...] ;; collection binding [?x ...]
+        (reduce sum-rel
+          (map #(in->rel (first form) %) value))
+      '[[*]]   ;; relation binding [[?a ?b]]
+        (reduce sum-rel
+          (map #(in->rel (first form) %) value))
+      '[*]     ;; tuple binding [?a ?b]
+        (reduce prod-rel
+          (map #(in->rel %1 %2) form value))
+      '_       ;; regular binding ?x
+        (Relation. {form 0} [#js [value]]))))
 
 (defn parse-rules [rules]
   (let [rules (if (string? rules) (cljs.reader/read-string rules) rules)] ;; for datascript.js interop
@@ -347,15 +354,15 @@
                      (context-resolve-val context f))
         [context production] (rel-prod-by-attrs context (filter symbol? args))
         tuple-fn (-call-fn context production fun args)
-        new-rel  (->> (:tuples production)
-                   (map #(let [val (tuple-fn %)
-                               rel (in->rel out val)]
-                             (prod-rel (Relation. (:attrs production) [%]) rel)))
-                   (reduce sum-rel))]
+        new-rel (if-let [tuples (not-empty (:tuples production))]
+                  (->> tuples
+                       (map #(let [val (tuple-fn %)
+                                   rel (in->rel out val)]
+                               (prod-rel (Relation. (:attrs production) [%]) rel)))
+                       (reduce sum-rel))
+                  (prod-rel production (in->rel out)))]
     (update-in context [:rels] conj new-rel)))
 
-
-
 ;;; RULES
 
 (defn rule? [context clause]

test/test/datascript.cljs

@@ -569,7 +569,15 @@
                            [(+ ?a1 ?a2) ?a12]
                            [(= ?a12 ?a3)]]
                   db)
-             #{[1 2 3] [2 1 3]})))))
+             #{[1 2 3] [2 1 3]})))
+
+    (testing "Function on empty rel"
+      (is (= (d/q '[:find  ?e ?y
+                    :where [?e :salary ?x]
+                           [(+ ?x 100) ?y]]
+                  [[0 :age 15] [1 :age 35]])
+             #{})))
+    ))
 
 
 (deftest test-rules
@@ -960,3 +968,4 @@
       (is (= db (cljs.reader/read-string (pr-str db)))))))
 
 ;; (t/test-ns 'test.datascript)
+