2.4 Join Fetch

By default, Jimmer uses batch-optimized additional queries to fetch associated objects.

However, for reference association properties (i.e., non-collection associations, @ManyToOne or OneToOne), associated objects can be fetched alongside the current objects using SQL's left join.

Querying Dynamic Entities

Java

BookTable table = Tables.BOOK_TABLE;

List<Book> books = sqlClient
    .createQuery(table)
    .where(table.name().eq("GraphQL in Action"))
    .select(
        table.fetch(
            Fetchers.BOOK_FETCHER
                .allScalarFields()
                .store(
                    ReferenceFetchType.JOIN_ALWAYS,
                    Fetchers.BOOK_STORE_FETCHER
                            .allScalarFields()
                )
        )
    )
    .execute();

Kotlin

val books = sqlClient.createQuery(Book::class) {
    where(table.name eq "GraphQL in Action")
    select(
        table.fetchBy { 
            allScalarFields()
            store(
                ReferenceFetchType.JOIN_ALWAYS
            ) {
                allScalarFields()
            }
        }
    )
}

This generates the following SQL:

select
    tb_1_.ID,
    tb_1_.NAME,
    tb_1_.EDITION,
    tb_1_.PRICE,
    tb_2_.ID,
    tb_2_.NAME,
    tb_2_.WEBSITE
from BOOK tb_1_
left join BOOK_STORE tb_2_
    on tb_1_.STORE_ID = tb_2_.ID
where
    tb_1_.NAME = ? /* GraphQL in Action */

This feature only affects the underlying mechanism for fetching associated objects and has no impact on the upper-level functionality. The returned data is omitted here.

Querying Static DTOs

Create a file with a .dto extension in the src/main/dto folder and edit the code as follows:

Book.dto

export com.yourcompany.yourproject.model.BookStore
    -> package com.yourcompany.yourproject.model.dto

BookView {
    #allScalars(this)

    !fetchType(JOIN_ALWAYS)
    store {
        #allScalars
    }
}

Compile the project to generate the Java/Kotlin type BookView.

Java

BookTable table = Tables.BOOK_TABLE;

List<BookView> books = sqlClient
    .createQuery(table)
    .where(table.name().eq("GraphQL in Action"))
    .select(
        table.fetch(BookView.class)
    )
    .execute();

Kotlin

val books = sqlClient.createQuery(Book::class) {
    where(table.name eq "GraphQL in Action")
    select(
        table.fetch(BookView::class)
    )
}

The generated SQL has already been introduced earlier and will not be repeated here.

This feature only affects the underlying mechanism for fetching associated objects and has no impact on the upper-level functionality. The returned data is omitted here.