add extra test for ProjectionExpression using scan with ExpressionAttributes

moto/dynamodb2/models.py

@@ -985,6 +985,9 @@ class DynamoDBBackend(BaseBackend):
         else:
             filter_expression = Op(None, None)  # Will always eval to true
 
+        projection_expression = ','.join([expr_names[attr] if attr in expr_names else attr
+                                          for attr in projection_expression.replace(' ', '').split(',')])
+
         return table.scan(scan_filters, limit, exclusive_start_key, filter_expression, index_name, projection_expression)
 
     def update_item(self, table_name, key, update_expression, attribute_updates, expression_attribute_names,

moto/dynamodb2/responses.py

@@ -558,7 +558,7 @@ class DynamoHandler(BaseResponse):
         filter_expression = self.body.get('FilterExpression')
         expression_attribute_values = self.body.get('ExpressionAttributeValues', {})
         expression_attribute_names = self.body.get('ExpressionAttributeNames', {})
-        projection_expression = self.body.get('ProjectionExpression')
+        projection_expression = self.body.get('ProjectionExpression', '')
         exclusive_start_key = self.body.get('ExclusiveStartKey')
         limit = self.body.get("Limit")
         index_name = self.body.get('IndexName')

tests/test_dynamodb2/test_dynamodb.py

@@ -497,7 +497,7 @@ def test_basic_projection_expressions_using_scan():
         'subject': '123',
         'body': 'some other test message'
     })
-    # Test a query returning all items
+    # Test a scan returning all items
     results = table.scan(
         FilterExpression=Key('forum_name').eq(
             'the-key'),
@@ -603,6 +603,84 @@ def test_basic_projection_expressions_with_attr_expression_names():
     assert 'attachment' in results['Items'][0]
     assert results['Items'][0]['attachment'] == 'something'
 
+@mock_dynamodb2
+def test_basic_projection_expressions_using_scan_with_attr_expression_names():
+    dynamodb = boto3.resource('dynamodb', region_name='us-east-1')
+
+    # Create the DynamoDB table.
+    table = dynamodb.create_table(
+        TableName='users',
+        KeySchema=[
+            {
+                'AttributeName': 'forum_name',
+                'KeyType': 'HASH'
+            },
+            {
+                'AttributeName': 'subject',
+                'KeyType': 'RANGE'
+            },
+        ],
+        AttributeDefinitions=[
+            {
+                'AttributeName': 'forum_name',
+                'AttributeType': 'S'
+            },
+            {
+                'AttributeName': 'subject',
+                'AttributeType': 'S'
+            },
+        ],
+        ProvisionedThroughput={
+            'ReadCapacityUnits': 5,
+            'WriteCapacityUnits': 5
+        }
+    )
+    table = dynamodb.Table('users')
+
+    table.put_item(Item={
+        'forum_name': 'the-key',
+        'subject': '123',
+        'body': 'some test message',
+        'attachment': 'something'
+    })
+
+    table.put_item(Item={
+        'forum_name': 'not-the-key',
+        'subject': '123',
+        'body': 'some other test message',
+        'attachment': 'something'
+    })
+    # Test a scan returning all items
+
+    results = table.scan(
+        FilterExpression=Key('forum_name').eq(
+            'the-key'),
+        ProjectionExpression='#rl, #rt, subject',
+        ExpressionAttributeNames={
+            '#rl': 'body',
+            '#rt': 'attachment'
+            },
+    )
+
+    assert 'body' in results['Items'][0]
+    assert 'attachment' in results['Items'][0]
+    assert 'subject' in results['Items'][0]
+    assert 'form_name' not in results['Items'][0]
+
+    # Test without a FilterExpression
+    results = table.scan(
+        ProjectionExpression='#rl, #rt, subject',
+        ExpressionAttributeNames={
+            '#rl': 'body',
+            '#rt': 'attachment'
+            },
+    )
+
+    assert 'body' in results['Items'][0]
+    assert 'attachment' in results['Items'][0]
+    assert 'subject' in results['Items'][0]
+    assert 'form_name' not in results['Items'][0]
+
 
 @mock_dynamodb2
 def test_put_item_returns_consumed_capacity():