13.5. Collection cache

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Hibernate can also cache collections, and the `@Cache` annotation must be on added to the collection property.

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If the collection is made of value types (basic or embeddables mapped with `@ElementCollection`),
the collection is stored as such.
If the collection contains other entities (`@OneToMany` or `@ManyToMany`),
the collection cache entry will store the entity identifiers only.

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<div class="title">Example 316. Collection cache mapping</div>
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<pre class="prettyprint highlight">`@OneToMany(mappedBy = "person", cascade = CascadeType.ALL)
@org.hibernate.annotations.Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
private List&lt;Phone&gt; phones = new ArrayList&lt;&gt;(  );`</pre>
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Collections are read-through, meaning they are cached upon being accessed for the first time:

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<div id="caching-collection-example" class="exampleblock">
<div class="title">Example 317. Collection cache usage</div>
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<pre class="prettyprint highlight">`Person person = entityManager.find( Person.class, 1L );
person.getPhones().size();`</pre>
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Subsequent collection retrievals will use the cache instead of going to the database.

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The collection cache is not write-through so any modification will trigger a collection cache entry invalidation.
On a subsequent access, the collection will be loaded from the database and re-cached.

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