Switch back to bag by default for list semantics
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Christian Beikov
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@ -84,22 +84,18 @@ include::{classificationTestsDir}/list/EntityWithList.java[tags=collections-list
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----
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====
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The ordering of a list is maintained as a column in the database to hold the element's index.
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This column can be configured via the `jakarta.persistence.OrderColumn` annotation.
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Contrary to natural expectations, the ordering of a list is by default not maintained.
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To maintain the order, it is necessary to explicitly use the `jakarta.persistence.OrderColumn` annotation.
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[[NOTE]]
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====
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Historically, Hibernate interpreted a `List` attribute without `@OrderColumn` as a BAG.
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Starting in 6.0, Hibernate allows to configure the default semantics of `List` without `@OrderColumn`
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via the `hibernate.mapping.default_list_semantics` setting.
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To switch to the more natural LIST semantics with an implicit order-column, set the setting to `LIST`.
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Starting in 6.0, however, Hibernate has moved to the more natural choice to map such
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Lists using LIST semantics with an implicit order-column. For applications needing backwards
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compatibility, Hibernate has added the `hibernate.mapping.default_list_semantics` setting. To
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achieve the legacy behavior, set `hibernate.mapping.default_list_semantics=bag`
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The default column name that stores the index is derived from the attribute name, by suffixing `_ORDER`.
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====
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The mapping above would store the index in a column named `names_ORDER`, per the default
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for `jakarta.persistence.OrderColumn#name`. We can also explicitly name the column to use; e.g.
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[[collection-list-ordercolumn-ex]]
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.@OrderColumn
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====
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@ -478,7 +478,7 @@ public class MetadataBuilderImpl implements MetadataBuilderImplementor, TypeCont
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}
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return classification;
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},
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CollectionClassification.LIST
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CollectionClassification.BAG
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);
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}
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@ -812,19 +812,13 @@ public interface AvailableSettings {
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* Hibernate detects a plural attribute typed as {@link java.util.List} with no explicit
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* list index configuration.
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* <p/>
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* Historically Hibernate interpreted this using
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* {@linkplain org.hibernate.metamodel.CollectionClassification#BAG BAG} semantics.
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* Starting in 6.0, Hibernate now interprets this situation using
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* {@linkplain org.hibernate.metamodel.CollectionClassification#LIST LIST} semantics.
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* <p/>
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* Accepts any of:
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* <ul>
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* <li>an instance of {@code CollectionClassification}
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* <li>the (case insensitive) name of a {@code CollectionClassification} (bag e.g.)
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* <li>the (case insensitive) name of a {@code CollectionClassification} (list e.g.)
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* <li>a {@link Class} representing either {@link java.util.List} or {@link java.util.Collection}
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* </ul>
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* <p/>
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* Backwards compatibility can be achieved by specifying `hibernate.mapping.default_list_semantics=bag` e.g.
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*
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* @since 6.0
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*/
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@ -21,6 +21,5 @@ hibernate.cache.region_prefix hibernate.test
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hibernate.cache.region.factory_class org.hibernate.testing.cache.CachingRegionFactory
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hibernate.service.allow_crawling=false
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## backwards compatibility wrt bag v. list for "implicit" List mappings
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hibernate.mapping.default_list_semantics=bag
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## make sure we use bag semantics for "implicit" List mappings
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hibernate.mapping.default_list_semantics=bag
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@ -260,42 +260,6 @@ plural attribute classification
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See https://docs.jboss.org/hibernate/orm/6.0/userguide/html_single/Hibernate_User_Guide.html#collection-type-reg-ann
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for details of using `@CollectionTypeRegistration`
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[[collection-list-as-bag]]
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==== List as BAG
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Historically, Hibernate treated `List` attributes with no explicit ordering details using its
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BAG semantics.
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```
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@ElementCollection
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List<String> names;
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```
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This is not the most natural decision and is rooted in the original annotation
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support being too closely related to the `hbm.xml` mapping format.
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Starting in 6.0, Hibernate now makes the more natural interpretation of such a mapping using its
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LIST semantics. It treats the above example with an implicit an `@OrderColumn`. The above mapping
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is now equivalent to
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```
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@ElementCollection
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@OrderColumn(...)
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List<String> names;
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```
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A new "compatibility flag" has been added to allow continuing with the legacy behavior:
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```
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hibernate.mapping.default_list_semantics=bag
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```
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The same can be achieved for specific attributes using the new `@Bag` annotation as well.
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=== Misc
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* The default type for `Duration` was changed to `NUMERIC` which could lead to schema validation errors
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