Planned lessonJNR-026-L03

Mapping rows

Lesson 3 of 5
Junior

On This Lesson 4 topics

In this lesson
Planned topics
Draft outline details
Practice

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In this lesson

turn result rows into records.

Planned topics

A RowMapper<T> converts one row to one object; Spring loops over the rows.
You never call rs.next() yourself.
query(Product.class) maps columns to record components or properties automatically (names must match; created_at matches createdAt).
Write a mapper when types need conversion, for example timestamptz to Instant.
Keep mapping inside the repository; services never see ResultSet.

Draft outline details

Demonstration

java

private static final RowMapper<Product> MAPPER = (rs, i) -> new Product(
        rs.getLong("id"),
        rs.getString("name"),
        rs.getBigDecimal("price"));

Check your understanding

Who calls rs.next() when you use a RowMapper?

Show answer

Spring.

Practice

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