readmodels

Read models are representations of application data optimized for read operations. In architecture terms, they are the query side in a Command Query Responsibility Segregation (CQRS) pattern, separating the models used to modify data from those used to read it. Read models are typically projections built from domain events or from the write model, and they provide query-optimized structures rather than fully normalized domain entities.

Construction and maintenance: Read models are usually created by projections or materialized views that subscribe to changes on the write side. Each update to the write model produces one or more read-model updates. They may be stored in a variety of data stores, including relational databases, document stores, key-value stores, or search indexes, chosen to suit the queries they must support. Updates can be synchronous to achieve strong consistency or asynchronous to improve throughput and scalability; most implementations use eventual consistency.

Design characteristics: Read models are often denormalized and tailored for specific query patterns. They may contain computed fields, aggregated totals, or pre-joined data to avoid expensive joins at query time. They usually carry versioning or timestamps to help detect out-of-date data, and update logic is designed to be idempotent.

Advantages and trade-offs: Read models reduce query latency and simplify complex reads, but they add complexity, require synchronization between write and read sides, and increase data duplication. Monitoring, testing, and schema evolution are essential.

Alternatives: A single model serving both reads and writes, or caches and materialized views within a monolithic system, can be used when CQRS overhead is undesirable.