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POHow to use second level cache for lazy loaded collections in Hibernate?
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  1. POHow to use second level cache for lazy loaded collections in Hibernate?
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    copied!<p>Let's say I have two entities, <code>Employee</code> and <code>Skill</code>. Every employee has a set of skills. Now when I load the skills lazily through the <code>Employee</code> instances the cache is not used for skills in different instances of <code>Employee</code>.</p> <p>Let's Consider the following data set.</p> <pre><code>Employee - 1 : Java, PHP Employee - 2 : Java, PHP </code></pre> <p>When I load Employee - 2 after Employee - 1, I do not want hibernate to hit the database to get the skills and instead use the <code>Skill</code> instances already available in cache. Is this possible? If so how?</p> <p><strong>Hibernate Configuration</strong></p> <pre><code>&lt;session-factory&gt; &lt;property name="hibernate.connection.driver_class"&gt;com.mysql.jdbc.Driver&lt;/property&gt; &lt;property name="hibernate.connection.password"&gt;pass&lt;/property&gt; &lt;property name="hibernate.connection.url"&gt;jdbc:mysql://localhost/cache&lt;/property&gt; &lt;property name="hibernate.connection.username"&gt;root&lt;/property&gt; &lt;property name="hibernate.dialect"&gt;org.hibernate.dialect.MySQLInnoDBDialect&lt;/property&gt; &lt;property name="hibernate.cache.use_second_level_cache"&gt;true&lt;/property&gt; &lt;property name="hibernate.cache.use_query_cache"&gt;true&lt;/property&gt; &lt;property name="hibernate.cache.provider_class"&gt;net.sf.ehcache.hibernate.EhCacheProvider&lt;/property&gt; &lt;property name="hibernate.hbm2ddl.auto"&gt;update&lt;/property&gt; &lt;property name="hibernate.show_sql"&gt;true&lt;/property&gt; &lt;mapping class="org.cache.models.Employee" /&gt; &lt;mapping class="org.cache.models.Skill" /&gt; &lt;/session-factory&gt; </code></pre> <p><strong>The Entities with imports, getters and setters Removed</strong></p> <pre><code>@Entity @Table(name = "employee") @Cache(usage = CacheConcurrencyStrategy.READ_WRITE) public class Employee { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private int id; private String name; public Employee() { } @ManyToMany @JoinTable(name = "employee_skills", joinColumns = @JoinColumn(name = "employee_id"), inverseJoinColumns = @JoinColumn(name = "skill_id")) @Cache(usage = CacheConcurrencyStrategy.READ_WRITE) private List&lt;Skill&gt; skills; } @Entity @Table(name = "skill") @Cache(usage = CacheConcurrencyStrategy.READ_WRITE) public class Skill { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private int id; private String name; } </code></pre> <p><strong>SQL for Loading the Second Employee and his Skills</strong></p> <pre><code>Hibernate: select employee0_.id as id0_0_, employee0_.name as name0_0_ from employee employee0_ where employee0_.id=? Hibernate: select skills0_.employee_id as employee1_1_, skills0_.skill_id as skill2_1_, skill1_.id as id1_0_, skill1_.name as name1_0_ from employee_skills skills0_ left outer join skill skill1_ on skills0_.skill_id=skill1_.id where skills0_.employee_id=? </code></pre> <p>In that I specifically want to avoid the second query as the first one is unavoidable anyway.</p>
 

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