fix: ensures parser can take json strings as input

Author: heitorlessa

aws_lambda_powertools/utilities/parser/parser.py

@@ -149,6 +149,9 @@ def handler(event: Order, context: LambdaContext):
 
     try:
         logger.debug("Parsing and validating event model; no envelope used")
+        if isinstance(event, str):
+            return model.parse_raw(event)
+
         return model.parse_obj(event)
     except (ValidationError, TypeError) as e:
         raise ModelValidationError("Input event does not conform with model") from e

docs/content/utilities/parser.mdx

@@ -59,7 +59,7 @@ These are simply Python classes that inherit from BaseModel. **Parser** enforces
 
 ## Parsing events
 
-You can parse inbound events using **event_parser** decorator, or the standalone `parse` function.
+You can parse inbound events using **event_parser** decorator, or the standalone `parse` function. Both are also able to parse either dictionary or JSON string as an input.
 
 ### event_parser decorator
 
@@ -70,6 +70,20 @@ Use the decorator for fail fast scenarios where you want your Lambda function to
 ```python=:title=event_parser_decorator.py
 from aws_lambda_powertools.utilities.parser import parse, ModelValidationError
 from aws_lambda_powertools.utilities.typing import LambdaContext
+import json
+
+# Raw event for the Order model we've defined earlier
+payload = {
+    "id": 10876546789,
+    "description": "My order",
+    "items": [
+        {
+            "id": 1015938732,
+            "quantity": 1,
+            "description": "item xpto"
+        }
+    ]
+}
 
 @event_parser(model=Order) # highlight-line
 def handler(event: Order, context: LambdaContext):
@@ -79,6 +93,9 @@ def handler(event: Order, context: LambdaContext):
 
     order_items = [items for item in event.items]
     ...
+
+handler(event=payload, context=LambdaContext())
+handler(event=json.dumps(payload), context=LambdaContext()) # also works if event is a JSON string
 ```
 
 ### parse function
@@ -113,6 +130,10 @@ def my_function():
         }
 ```
 
+### Error handling
+
+**TBW**
+
 ## Built-in envelopes
 
 **TBW**

tests/functional/parser/test_parser.py

@@ -1,4 +1,5 @@
-from typing import Dict
+import json
+from typing import Dict, Union
 
 import pytest
 
@@ -55,3 +56,13 @@ def handle_no_envelope(event: Dict, _: LambdaContext):
 
     with pytest.raises(exceptions.InvalidModelTypeError):
         handle_no_envelope(event=dummy_event, context=LambdaContext())
+
+
+def test_parser_event_as_json_string(dummy_event, dummy_schema):
+    dummy_event = json.dumps(dummy_event["payload"])
+
+    @event_parser(model=dummy_schema)
+    def handle_no_envelope(event: Union[Dict, str], _: LambdaContext):
+        return event
+
+    handle_no_envelope(dummy_event, LambdaContext())