2.6.7. Interpreting AUTO

<div class="paragraph">

How a persistence provider interprets the AUTO generation type is left up to the provider.

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The default behavior is to look at the java type of the identifier attribute.

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If the identifier type is UUID, Hibernate is going to use an [UUID identifier](#identifiers-generators-uuid).

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If the identifier type is numerical (e.g. `Long`, `Integer`), then Hibernate is going to use the `IdGeneratorStrategyInterpreter` to resolve the identifier generator strategy.
The `IdGeneratorStrategyInterpreter` has two implementations:

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<div class="dlist">
<dl>
<dt class="hdlist1">`FallbackInterpreter`</dt>
<dd>

This is the default strategy since Hibernate 5.0. For older versions, this strategy is enabled through the [`hibernate.id.new_generator_mappings`](#configurations-mapping) configuration property .
When using this strategy, `AUTO` always resolves to `SequenceStyleGenerator`.
If the underlying database supports sequences, then a SEQUENCE generator is used. Otherwise, a TABLE generator is going to be used instead.

</dd>
<dt class="hdlist1">`LegacyFallbackInterpreter`</dt>
<dd>

This is a legacy mechanism that was used by Hibernate prior to version 5.0 or when the [`hibernate.id.new_generator_mappings`](#configurations-mapping) configuration property is false.
The legacy strategy maps `AUTO` to the `native` generator strategy which uses the [Dialect#getNativeIdentifierGeneratorStrategy](https://docs.jboss.org/hibernate/orm/5.2/javadocs/org/hibernate/dialect/Dialect.html#getNativeIdentifierGeneratorStrategy--) to resolve the actual identifier generator (e.g. `identity` or `sequence`).

</dd>
</dl>
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<div class="sect3">