The correct answer is Document database.

Document database systems are schemaless and store entities as JSON or JSON like documents so all of an entity's fields and any nested data remain together in a single document. This model allows you to read or write an entire entity with one operation which matches the description in the question.

Wide column store systems organize data into rows with dynamic columns and they are optimized for sparse data and wide tables rather than storing each entity as a single JSON document. They use column families and a different storage model.

Graph database systems model data as nodes and edges and they are optimized for relationship queries and traversals. They do not primarily store whole entities as JSON documents in a single document.

Time series database systems are specialized for timestamped metrics and events and they focus on efficient storage and querying of sequences over time rather than schemaless JSON documents for full entities.

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