# How to Typesafely Map a Nested SQL Collection into a Nested Java Map with jOOQ

DevFeed: [How to Typesafely Map a Nested SQL Collection into a Nested Java Map with jOOQ](<https://devfeed.tech/articles/how-to-typesafely-map-a-nested-sql-collection-into-a-nested-java-map-with-jooq-28946.md>)

Original publisher: [Read original article](<https://blog.jooq.org/how-to-typesafely-map-a-nested-sql-collection-into-a-nested-java-map-with-jooq/>)

Author: lukaseder

Published: 2022-05-09T10:06:51Z

Content type: tutorial

Language: en

Sources: [jOOQ](<https://devfeed.tech/sources/jooq.md>)

Topics: [Java](<https://devfeed.tech/topics/java.md>), [SQL](<https://devfeed.tech/topics/sql.md>), [Databases](<https://devfeed.tech/topics/databases.md>), [data](<https://devfeed.tech/topics/data.md>), [Structured-data](<https://devfeed.tech/topics/structured-data.md>)

Tags: [collections](<https://devfeed.tech/tags/collections.md>), [data](<https://devfeed.tech/tags/data.md>), [data-structures](<https://devfeed.tech/tags/data-structures.md>), [how-to](<https://devfeed.tech/tags/how-to.md>), [java](<https://devfeed.tech/tags/java.md>), [jooq](<https://devfeed.tech/tags/jooq.md>), [jooq-in-use](<https://devfeed.tech/tags/jooq-in-use.md>), [map](<https://devfeed.tech/tags/map.md>), [mapping](<https://devfeed.tech/tags/mapping.md>), [multiset](<https://devfeed.tech/tags/multiset.md>), [nested-collections](<https://devfeed.tech/tags/nested-collections.md>), [nested-maps](<https://devfeed.tech/tags/nested-maps.md>), [nested-records](<https://devfeed.tech/tags/nested-records.md>), [sql](<https://devfeed.tech/tags/sql.md>), [stack-overflow](<https://devfeed.tech/tags/stack-overflow.md>), [typesafety](<https://devfeed.tech/tags/typesafety.md>)

## AI overview

This tutorial shows how to use jOOQ 3.15's ad-hoc conversion API and nested collection features to map a nested SQL collection into a type-safe nested Java Map. It uses the Sakila database example and explains how collectors preserve insertion order.

## Source excerpt

A really cool, recent question on Stack Overflow was about how to map a nested collection into a Java Map with jOOQ. In the past, I've blogged about the powerful MULTISET operator many times, which allows for nesting collections in jOOQ. This time, instead of nesting data into a List<UserType>, why not nest it in ... Continue reading How to Typesafely Map a Nested SQL Collection into a Nested Java Map with jOOQ ->