Fix partial update on simstring

embedding.go

@@ -382,16 +382,35 @@ func injectShadowVectors(ctx context.Context,
 			}
 
 			jsonTag := field.Tag.Get("json")
-			predicate := strings.Split(jsonTag, ",")[0]
+			jsonParts := strings.Split(jsonTag, ",")
+			predicate := jsonParts[0]
 			if predicate == "" {
 				predicate = field.Name
 			}
+			hasOmitempty := false
+			for _, opt := range jsonParts[1:] {
+				if opt == "omitempty" {
+					hasOmitempty = true
+					break
+				}
+			}
 			vecPred := vecShadowPredicate(predicate)
 
 			textVal := string(sv.Field(i).Interface().(SimString))
 			_, _, threshold := parseEmbeddingTag(dgraphTag)
 
-			// Below threshold (or empty): delete the shadow vector to avoid stale data.
+			// Empty + omitempty means the caller didn't set this field on a partial
+			// update. The primary predicate is omitted from the JSON mutation (so
+			// Dgraph never sees `fn_doc` and the existing string is preserved); the
+			// shadow vector must follow the same lifecycle, otherwise partial Updates
+			// (e.g. setting just an edge predicate) silently wipe vectors written by
+			// a prior Insert/Upsert. To explicitly clear a SimString, drop omitempty
+			// so the empty value reaches Dgraph and we delete the shadow vec below.
+			if textVal == "" && hasOmitempty {
+				continue
+			}
+
+			// Below threshold (or explicitly cleared): delete the shadow vector to avoid stale data.
 			if textVal == "" || (threshold > 0 && len([]rune(textVal)) < threshold) {
 				delNquads = append(delNquads, &api.NQuad{
 					Subject:     uid,

embedding_test.go

@@ -202,6 +202,64 @@ func TestUpdateWithEmbedding(t *testing.T) {
 	require.Equal(t, "updated text", provider.callLog[1])
 }
 
+// TestPartialUpdatePreservesShadowVector is a regression test for the
+// omitempty-aware skip in injectShadowVectors. A partial Update of a struct
+// that contains a SimString field (e.g. setting only UID + a non-SimString
+// field) must not delete the existing shadow vector. The primary predicate
+// is preserved by omitempty — Dgraph never sees the SimString in the mutation
+// NQuads — so the shadow path must follow the same lifecycle.
+//
+// Real-world failure that motivated this test: codebase-graph's indexer
+// upserts a Function with its doc comment in pass A, then issues a partial
+// `cli.Update(&Function{UID, Calls})` in pass B to add CALLS edges. Without
+// the omitempty skip, every pass-B Update silently wiped the doc-comment
+// vector written in pass A, leaving the shadow predicate sparse and breaking
+// similarity ranking once `similar_to`'s k saturated the candidate count.
+func TestPartialUpdatePreservesShadowVector(t *testing.T) {
+	const dims = 4
+	provider := newMockProvider(dims)
+	origVec := []float32{1.0, 0.0, 0.0, 0.0}
+	provider.register("the original description", origVec)
+
+	client, cleanup := createEmbeddingClient(t, provider)
+	defer cleanup()
+	ctx := context.Background()
+
+	p := &embeddableProduct{Name: "Thing", Description: "the original description"}
+	require.NoError(t, client.Insert(ctx, p))
+	require.NotEmpty(t, p.UID)
+	require.Len(t, provider.callLog, 1, "Insert should embed once")
+
+	findByOrigVec := func(t *testing.T) string {
+		t.Helper()
+		dgoClient, cleanupDgo, err := client.DgraphClient()
+		require.NoError(t, err)
+		defer cleanupDgo()
+		var result embeddableProduct
+		tx := dg.NewReadOnlyTxn(dgoClient)
+		err = mg.SimilarTo(tx, &result, "description", origVec, 1).Scan()
+		require.NoError(t, err)
+		return result.UID
+	}
+
+	// Sanity: shadow vec is reachable after Insert.
+	require.Equal(t, p.UID, findByOrigVec(t),
+		"shadow vec should be present after Insert")
+
+	// Partial Update: only UID + a non-SimString field. Description is the
+	// zero value and is omitted from the mutation by omitempty — the primary
+	// predicate is preserved, and the shadow vec must be too.
+	require.NoError(t, client.Update(ctx, &embeddableProduct{UID: p.UID, Name: "Thing v2"}))
+
+	// Provider must NOT be re-invoked — there's nothing to embed.
+	require.Len(t, provider.callLog, 1,
+		"partial Update must not re-embed when SimString is unset")
+
+	// Shadow vec must survive the partial update — this is the regression assertion.
+	require.Equal(t, p.UID, findByOrigVec(t),
+		"shadow vec must survive partial Update of unrelated fields")
+}
+
 func TestSimilarToQuery(t *testing.T) {
 	const dims = 5
 	provider := newMockProvider(dims)