16.8. Roots

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Roots define the basis from which all joins, paths and attributes are available in the query.
A root is always an entity type. Roots are defined and added to the criteria by the overloaded from methods on `javax.persistence.criteria.CriteriaQuery`:

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<div class="title">Example 415. Root methods</div>
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<pre class="prettyprint highlight">`&lt;X&gt; Root&lt;X&gt; from( Class&lt;X&gt; );

&lt;X&gt; Root&lt;X&gt; from( EntityType&lt;X&gt; );`</pre>
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<div class="title">Example 416. Adding a root example</div>
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<pre class="prettyprint highlight">`CriteriaBuilder builder = entityManager.getCriteriaBuilder();

CriteriaQuery&lt;Person&gt; criteria = builder.createQuery( Person.class );
Root&lt;Person&gt; root = criteria.from( Person.class );`</pre>
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Criteria queries may define multiple roots, the effect of which is to create a Cartesian Product between the newly added root and the others.
Here is an example defining a Cartesian Product between `Person` and `Partner` entities:

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<div class="title">Example 417. Adding multiple roots example</div>
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<pre class="prettyprint highlight">`CriteriaBuilder builder = entityManager.getCriteriaBuilder();

CriteriaQuery&lt;Tuple&gt; criteria = builder.createQuery( Tuple.class );

Root&lt;Person&gt; personRoot = criteria.from( Person.class );
Root&lt;Partner&gt; partnerRoot = criteria.from( Partner.class );
criteria.multiselect( personRoot, partnerRoot );

Predicate personRestriction = builder.and(
    builder.equal( personRoot.get( Person_.address ), address ),
    builder.isNotEmpty( personRoot.get( Person_.phones ) )
);
Predicate partnerRestriction = builder.and(
    builder.like( partnerRoot.get( Partner_.name ), prefix ),
    builder.equal( partnerRoot.get( Partner_.version ), 0 )
);
criteria.where( builder.and( personRestriction, partnerRestriction ) );

List&lt;Tuple&gt; tuples = entityManager.createQuery( criteria ).getResultList();`</pre>
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