DynamoDB Mapper中含连字符键名引发语法错误的解决咨询

Got it, let's break down why you're still hitting that syntax error even after setting up Expression Attribute Names (EANs). The root issue almost always comes down to not actually using your EAN placeholder in the KeyConditionExpression itself.

DynamoDB's expression syntax doesn't allow attribute names with hyphens (or other special characters like spaces) to be used directly. You have to replace them with a placeholder (like #k in your code) everywhere you reference the attribute—including in the KeyConditionExpression.

Here's the Correct Implementation #

Let's walk through a complete, working example using DynamoDB Mapper:

// 1. Map your hyphenated attribute name to a placeholder
Map<String, String> expressionAttributeNames = new HashMap<>();
expressionAttributeNames.put("#fb", "foo-bar"); 

// 2. Define your attribute value
Map<String, AttributeValue> expressionAttributeValues = new HashMap<>();
expressionAttributeValues.put(":val", AttributeValue.builder().s("your-target-value").build());

// 3. Build the Key Condition Expression using ONLY the placeholder
String keyConditionExpression = "#fb = :val";

// 4. Assemble the query expression with all required components
DynamoDBQueryExpression<YourModelClass> queryExpr = new DynamoDBQueryExpression<>();
queryExpr.setKeyConditionExpression(keyConditionExpression);
queryExpr.setExpressionAttributeNames(expressionAttributeNames);
queryExpr.setExpressionAttributeValues(expressionAttributeValues);
// Add any other required parameters (e.g., hash key filters) here

// 5. Run the query with your DynamoDB Mapper
List<YourModelClass> results = dynamoDBMapper.query(YourModelClass.class, queryExpr);

Common Mistakes to Avoid #

• Forgetting to replace the original attribute name: If your KeyConditionExpression still uses foo-bar = :v instead of #fb = :val, you'll get the same syntax error. Double-check that every reference to the hyphenated attribute uses the placeholder.
• Typos in placeholder names: Make sure the placeholder in your expression matches exactly what you defined in ExpressionAttributeNames (e.g., don't map #fb but use #k in the expression).
• Missing EANs in the request: Ensure you're actually passing the expressionAttributeNames map to your DynamoDBQueryExpression—it's easy to overlook this critical step.

Why This Works #

By using the EAN placeholder, you're telling DynamoDB to substitute #fb with the actual attribute name foo-bar when evaluating the expression. This bypasses the syntax restriction on special characters in attribute names entirely.

内容的提问来源于stack exchange，提问作者Sandeep Rao