Fixed find-datom on empty DB (closes #477)

Author: tonsky

CHANGELOG.md

@@ -1,3 +1,7 @@
+# WIP
+
+- Fixed `find-datom` on empty DB #477 thx @RCmerci
+
 # 1.7.2 - Jul 4, 2024
 
 - Regression: transacting many ref value as a set of inline maps #476 

src/datascript/db.cljc

@@ -1149,7 +1149,7 @@
         cmp     #?(:clj (.comparator ^clojure.lang.Sorted set) :cljs (.-comparator set))
         from    (components->pattern db index c0 c1 c2 c3 e0 tx0)
         to      (components->pattern db index c0 c1 c2 c3 emax txmax)
-        datom   (when-let [set* (seq set)] (first (set/seek set* from)))]
+        datom   (some-> set seq (set/seek from) first)]
     (when (and (some? datom) (<= 0 (cmp to datom)))
       datom)))
 

test/datascript/test/index.cljc

@@ -102,7 +102,11 @@
     (is (= [2 :name "Ivan"] (dvec (d/find-datom db :eavt 2 :name))))
 
     (is (= nil (dvec (d/find-datom db :eavt 1 :name "Ivan"))))
-    (is (= nil (dvec (d/find-datom db :eavt 4))))))
+    (is (= nil (dvec (d/find-datom db :eavt 4))))
+    
+    ;; issue-477
+    (is (= nil (d/find-datom (d/empty-db) :eavt)))
+    (is (= nil (d/find-datom (d/empty-db {:age {:db/index true}}) :eavt)))))
 
 (deftest test-seek-datoms
   (let [dvec #(vector (:e %) (:a %) (:v %))