Introduction to Amazon DynamoDB Query

Amazon DynamoDB is a fully managed NoSQL database service provided by Amazon Web Services (AWS) that offers fast and predictable performance with seamless scalability. DynamoDB is particularly effective for applications that require consistent latency and massive throughput. In this guide, we'll focus on querying items whose key contains a specific substring using DynamoDB.

Understanding DynamoDB Query Operations

DynamoDB supports two primary operations to access data:

• Scan: Examines every item in the table and returns all data attributes by default. This operation can be resource-intensive and is not usually recommended for large datasets when efficiency is a priority.
• Query: More efficient than scanning because it can retrieve items based on a primary key or global secondary index. The query operation allows you to filter results, but this filtering happens after the query processes all its data.

For DynamoDB tables with a large number of items, the `Query` operation is usually preferred due to its performance advantages.

Using Query with Key Substring

DynamoDB's query operation on string data types is limited to using either the partition key or sort key with full match conditions or sort key with specific conditions such as begins with. Unfortunately, DynamoDB does not support full-fledged `contains` operations on keys directly during a query operation. To handle substring match scenarios, an additional approach dealing with attribute values rather than keys can be taken. Here we'll consider best practices and strategies associated with this approach.

Approaches to Solve Key Substring Queries

1. Design Adjustment: Often, problems arise from requiring features that differ from DynamoDB's typical access patterns. Re-evaluate your data model to see if you can modify design, possibly through denormalization or indexing attributes differently, to facilitate expected queries.
2. Use of Filter Expressions: While direct substring queries aren’t possible with the keys themselves, you can query against attributes (non-key values) using filter expressions.