function to add an element to an array and get all unique elements only

postgres/jsonb_array_add_distinct.sql

@@ -0,0 +1,23 @@
+CREATE OR REPLACE FUNCTION public.jsonb_array_add_distinct(_arr jsonb, _add text) RETURNS jsonb AS
+$$
+DECLARE
+    _ret jsonb;
+
+BEGIN
+
+SELECT 
+    jsonb_agg(DISTINCT x.ae)
+INTO
+    _ret
+FROM
+    (
+        SELECT jsonb_array_elements_text(_arr) ae
+        UNION ALL 
+        SELECT _add ae
+    ) x;
+
+RETURN _ret;
+
+END;
+$$
+language plpgsql