11.10. FetchMode.SUBSELECT

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To demonstrate how `FetchMode.SUBSELECT` works, we are going to modify the [`FetchMode.SELECT` mapping example](#fetching-strategies-fetch-mode-select-mapping-example) to use
`FetchMode.SUBSELECT`:

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<div id="fetching-strategies-fetch-mode-subselect-mapping-example" class="exampleblock">
<div class="title">Example 294. `FetchMode.SUBSELECT` mapping example</div>
<div class="content">
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight">`@OneToMany(mappedBy = "department", fetch = FetchType.LAZY)
@Fetch(FetchMode.SUBSELECT)
private List&lt;Employee&gt; employees = new ArrayList&lt;&gt;();`</pre>
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<div class="paragraph">

Now, we are going to fetch all `Department` entities that match a given filtering criteria
and then navigate their `employees` collections.

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<div class="paragraph">

Hibernate is going to avoid the N+1 query issue by generating a single SQL statement to initialize all `employees` collections
for all `Department` entities that were previously fetched.
Instead of using passing all entity identifiers, Hibernate simply reruns the previous query that fetched the `Department` entities.

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<div id="fetching-strategies-fetch-mode-subselect-example" class="exampleblock">
<div class="title">Example 295. `FetchMode.SUBSELECT` mapping example</div>
<div class="content">
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight">`List&lt;Department&gt; departments = entityManager.createQuery(
    "select d " +
    "from Department d " +
    "where d.name like :token", Department.class )
.setParameter( "token", "Department%" )
.getResultList();

log.infof( "Fetched %d Departments", departments.size());

for (Department department : departments ) {
    assertEquals( 3, department.getEmployees().size() );
}`</pre>
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<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight">`SELECT
    d.id as id1_0_
FROM
    Department d
where
    d.name like 'Department%'

-- Fetched 2 Departments

SELECT
    e.department_id as departme3_1_1_,
    e.id as id1_1_1_,
    e.id as id1_1_0_,
    e.department_id as departme3_1_0_,
    e.username as username2_1_0_
FROM
    Employee e
WHERE
    e.department_id in (
        SELECT
            fetchmodes0_.id
        FROM
            Department fetchmodes0_
        WHERE
            d.name like 'Department%'
    )`</pre>
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<div class="sect2">