Where does repository abstraction stop?

Goal & mental model verified

Spring Data builds repository abstractions around store-specific behavior. JPA has persistence-context and relationship semantics; Data JDBC uses a simpler aggregate model. Derived queries reduce boilerplate without replacing query design.

Worked example · design exercise synthesis

A broker dashboard pages quotes by tenant and status. Use a response projection and a deliberate fetch plan instead of traversing every policy relationship during JSON serialization.

Engineering decision synthesis

Choose JPA when its entity model helps; choose JDBC-style access when explicit aggregate operations fit. R2DBC is a non-blocking access model, not reactive JPA.

Pitfall & diagnosis synthesis

A compact repository method can still produce expensive SQL. N+1 access and loading oversized graphs should be diagnosed through executed queries and row counts, not annotation counts.

Improve & validate synthesis

Capture SQL and query plans for representative tenant sizes. Validate pagination and fetch plans together; compare query count and end-to-end latency after changes.