From 96c2506fd416db910002178cdcad00e113ef2d93 Mon Sep 17 00:00:00 2001
From: Ber Zoidberg <ber.zoidberg@gmail.com>
Date: Tue, 11 Jun 2019 22:38:15 -0700
Subject: [PATCH] Fix DynamoDB UpdateExpression support for REMOVE on nested
 maps

---
 moto/dynamodb2/models.py                      | 23 +++++++++++++++
 .../test_dynamodb_table_without_range_key.py  | 29 +++++++++++++++++++
 2 files changed, 52 insertions(+)

diff --git a/moto/dynamodb2/models.py b/moto/dynamodb2/models.py
index 6bcde41b2..2f6575354 100644
--- a/moto/dynamodb2/models.py
+++ b/moto/dynamodb2/models.py
@@ -149,6 +149,29 @@ class Item(BaseModel):
                     value = re.sub(r'{0}\b'.format(k), v, value)
 
                 if action == "REMOVE":
+                    key  = value
+                    if '.' not in key:
+                        self.attrs.pop(value, None)
+                    else:
+                        # Handle nested dict updates
+                        key_parts = key.split('.')
+                        attr = key_parts.pop(0)
+                        if attr not in self.attrs:
+                            raise ValueError
+
+                        last_val = self.attrs[attr].value
+                        for key_part in key_parts[:-1]:
+                            # Hack but it'll do, traverses into a dict
+                            last_val_type = list(last_val.keys())
+                            if last_val_type and last_val_type[0] == 'M':
+                                    last_val = last_val['M']
+
+                            if key_part not in last_val:
+                                last_val[key_part] = {'M': {}}
+
+                            last_val = last_val[key_part]
+
+                        last_val.pop(key_parts[-1], None)
                     self.attrs.pop(value, None)
                 elif action == 'SET':
                     key, value = value.split("=", 1)
diff --git a/tests/test_dynamodb2/test_dynamodb_table_without_range_key.py b/tests/test_dynamodb2/test_dynamodb_table_without_range_key.py
index 1880c7cab..d882b14a6 100644
--- a/tests/test_dynamodb2/test_dynamodb_table_without_range_key.py
+++ b/tests/test_dynamodb2/test_dynamodb_table_without_range_key.py
@@ -450,6 +450,35 @@ def test_update_item_remove():
     })
 
 
+@mock_dynamodb2_deprecated
+def test_update_item_nested_remove():
+    conn = boto.dynamodb2.connect_to_region("us-east-1")
+    table = Table.create('messages', schema=[
+        HashKey('username')
+    ])
+
+    data = {
+        'username': "steve",
+        'Meta': {
+            'FullName': 'Steve Urkel'    
+        }
+    }
+    table.put_item(data=data)
+    key_map = {
+        'username': {"S": "steve"}
+    }
+
+    # Then remove the SentBy field
+    conn.update_item("messages", key_map,
+                     update_expression="REMOVE Meta.FullName")
+
+    returned_item = table.get_item(username="steve")
+    dict(returned_item).should.equal({
+        'username': "steve",
+        'Meta': {}
+    })
+
+
 @mock_dynamodb2_deprecated
 def test_update_item_set():
     conn = boto.dynamodb2.connect_to_region("us-east-1")