When would you cache an API response shape instead of a domain object?

Cache API responses versus domain objects

Compares caching response-shaped read models with caching domain entities or raw database objects.

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TL;DR

I would cache an API response or read model when the expensive part is building that exact response and the same shape is reused often. That can avoid repeated joins, projection, and serialization work. I would be more careful caching domain objects because they may contain fields the API does not need, private data, navigation graphs, or behavior that does not survive serialization cleanly.

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DTO caching, domain model safety, serialization, versioning, permissions, over-fetching, and read-model ownership.

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Why this question matters
What is cached matters as much as where it is cached. Caching the wrong shape creates coupling and hard-to-debug stale behavior.
I would cache an API response or read model when the expensive part is building that exact response and the same shape is reused often. That can avoid repeated joins, projection, and serialization work. I would be more careful caching domain objects because they may contain fields the API does not need, private data, navigation graphs, or behavior that does not survive serialization cleanly.
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A response-shaped cache works well for read-heavy endpoints with stable contracts, clear keys, and acceptable freshness. The key needs to include filters, tenant, locale, permissions, and response version. Domain-object caching can be useful for small reference data inside a bounded service, but it should not leak persistence details into API contracts or bypass domain rules. I prefer caching the thing I can invalidate and reason about.

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Details

Caching EF entities with navigation graphs directly.
Reusing a cached response across users with different permissions.
Forgetting serialized shape changes during deployment.
Caching too broad a shape and increasing memory pressure.

When would you cache an API response shape instead of a domain object?

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