Feat: conversation variable & variable assigner node (#7222)

Signed-off-by: -LAN- <laipz8200@outlook.com>
Co-authored-by: Joel <iamjoel007@gmail.com>
Co-authored-by: -LAN- <laipz8200@outlook.com>

api/models/types.py

@@ -0,0 +1,26 @@
+from sqlalchemy import CHAR, TypeDecorator
+from sqlalchemy.dialects.postgresql import UUID
+
+
+class StringUUID(TypeDecorator):
+    impl = CHAR
+    cache_ok = True
+
+    def process_bind_param(self, value, dialect):
+        if value is None:
+            return value
+        elif dialect.name == 'postgresql':
+            return str(value)
+        else:
+            return value.hex
+
+    def load_dialect_impl(self, dialect):
+        if dialect.name == 'postgresql':
+            return dialect.type_descriptor(UUID())
+        else:
+            return dialect.type_descriptor(CHAR(36))
+
+    def process_result_value(self, value, dialect):
+        if value is None:
+            return value
+        return str(value)