From c9d69681ece1baeee088baf449a9273b921c941d Mon Sep 17 00:00:00 2001
From: gruebel <anton.gruebel@gmail.com>
Date: Sun, 6 Oct 2019 16:49:02 +0200
Subject: [PATCH] Add evaluation of ConditionExpression to DynamoDB2
 delete_item

---
 moto/dynamodb2/models.py              | 17 ++++++++++++++---
 moto/dynamodb2/responses.py           | 18 ++++++++++++++++--
 tests/test_dynamodb2/test_dynamodb.py | 17 +++++++++++++++++
 3 files changed, 47 insertions(+), 5 deletions(-)

diff --git a/moto/dynamodb2/models.py b/moto/dynamodb2/models.py
index c06014488..b2ff7ffc3 100644
--- a/moto/dynamodb2/models.py
+++ b/moto/dynamodb2/models.py
@@ -1092,12 +1092,23 @@ class DynamoDBBackend(BaseBackend):
             item.update_with_attribute_updates(attribute_updates)
         return item
 
-    def delete_item(self, table_name, keys):
+    def delete_item(self, table_name, key, expression_attribute_names=None, expression_attribute_values=None,
+                    condition_expression=None):
         table = self.get_table(table_name)
         if not table:
             return None
-        hash_key, range_key = self.get_keys_value(table, keys)
-        return table.delete_item(hash_key, range_key)
+
+        hash_value, range_value = self.get_keys_value(table, key)
+        item = table.get_item(hash_value, range_value)
+
+        condition_op = get_filter_expression(
+            condition_expression,
+            expression_attribute_names,
+            expression_attribute_values)
+        if not condition_op.expr(item):
+            raise ValueError('The conditional request failed')
+
+        return table.delete_item(hash_value, range_value)
 
     def update_ttl(self, table_name, ttl_spec):
         table = self.tables.get(table_name)
diff --git a/moto/dynamodb2/responses.py b/moto/dynamodb2/responses.py
index d07beefd6..9e66a3342 100644
--- a/moto/dynamodb2/responses.py
+++ b/moto/dynamodb2/responses.py
@@ -579,7 +579,7 @@ class DynamoHandler(BaseResponse):
 
     def delete_item(self):
         name = self.body['TableName']
-        keys = self.body['Key']
+        key = self.body['Key']
         return_values = self.body.get('ReturnValues', 'NONE')
         if return_values not in ('ALL_OLD', 'NONE'):
             er = 'com.amazonaws.dynamodb.v20111205#ValidationException'
@@ -590,7 +590,21 @@ class DynamoHandler(BaseResponse):
             er = 'com.amazonaws.dynamodb.v20120810#ConditionalCheckFailedException'
             return self.error(er, 'A condition specified in the operation could not be evaluated.')
 
-        item = self.dynamodb_backend.delete_item(name, keys)
+        # Attempt to parse simple ConditionExpressions into an Expected
+        # expression
+        condition_expression = self.body.get('ConditionExpression')
+        expression_attribute_names = self.body.get('ExpressionAttributeNames', {})
+        expression_attribute_values = self.body.get('ExpressionAttributeValues', {})
+
+        try:
+            item = self.dynamodb_backend.delete_item(
+                name, key, expression_attribute_names, expression_attribute_values,
+                condition_expression
+            )
+        except ValueError:
+            er = 'com.amazonaws.dynamodb.v20111205#ConditionalCheckFailedException'
+            return self.error(er, 'A condition specified in the operation could not be evaluated.')
+
         if item and return_values == 'ALL_OLD':
             item_dict = item.to_json()
         else:
diff --git a/tests/test_dynamodb2/test_dynamodb.py b/tests/test_dynamodb2/test_dynamodb.py
index b0952f101..c4cf05c59 100644
--- a/tests/test_dynamodb2/test_dynamodb.py
+++ b/tests/test_dynamodb2/test_dynamodb.py
@@ -1995,6 +1995,23 @@ def test_condition_expressions():
             },
         )
 
+    with assert_raises(client.exceptions.ConditionalCheckFailedException):
+        client.delete_item(
+            TableName = 'test1',
+            Key = {
+                'client': {'S': 'client1'},
+                'app': {'S': 'app1'},
+            },
+            ConditionExpression = 'attribute_not_exists(#existing)',
+            ExpressionAttributeValues = {
+                ':match': {'S': 'match'}
+            },
+            ExpressionAttributeNames = {
+                '#existing': 'existing',
+                '#match': 'match',
+            },
+        )
+
 
 @mock_dynamodb2
 def test_condition_expression__attr_doesnt_exist():