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Now live: A fully responsive profile. P6Spy is a driver that does just that. Despite its age the last release dates from , it is not obsolete and server our purpose just fine.
It consists of the proxy driver itself and a properties configuration file spy. In order to leverage P6Spy feature, the only thing you have to do is to tell Hibernate to use a specific driver:. Of course, the configuration can go further. If you need to use P6Spy in an application server, the configuration should be done on the application server itself, at the datasource level. In Tomcat, for example, put spy. The source code for this article can be found here.
Thanks for visiting DZone today,. For this reason, it is very common to use a single reference time zone e. However, as explained in this article , this is not always practical, especially for front-end nodes.
For this reason, Hibernate offers the hibernate. With this configuration property in place, Hibernate is going to call the PreparedStatement. Timestamp, Calendar cal or PreparedStatement. Time x, Calendar cal , where the java. Calendar references the time zone provided via the hibernate.
Although Hibernate has long been offering custom types , as a JPA 2. In the following example, the java. To make use of this custom converter, the Convert annotation must decorate the entity attribute. When persisting such entity, Hibernate will do the type conversion based on the AttributeConverter logic:. In cases when the Java type specified for the "database side" of the conversion the second AttributeConverter bind parameter is not known, Hibernate will fallback to a java.
Serializable type. Therefore, mutability is given by the JavaTypeDescriptor getMutabilityPlan of the associated entity attribute type. If the entity attribute is a String , a primitive wrapper e. Integer , Long an Enum type, or any other immutable Object type, then you can only change the entity attribute value by reassigning it to a new value. Considering we have the same Period entity attribute as illustrated in the JPA 2.
On the other hand, consider the following example where the Money type is a mutable. A mutable Object allows you to modify its internal structure, and Hibernate dirty checking mechanism is going to propagate the change to the database:. Although the AttributeConverter types can be mutable so that dirty checking, deep copying, and second-level caching work properly, treating these as immutable when they really are is more efficient.
You can force Hibernate to quote an identifier in the generated SQL by enclosing the table or column name in backticks in the mapping document. Once the reserved keywords are escaped, Hibernate will use the correct quotation style for the SQL Dialect. Because name and number are reserved words, the Product entity mapping uses backticks to quote these column names.
Hibernate can also quote all identifiers e. When persisting a Product entity, Hibernate is going to quote all identifiers as in the following example:. For more about quoting-related configuration properties, check out the Mapping configurations section as well.
Generated properties are properties that have their values generated by the database. Typically, Hibernate applications needed to refresh objects that contain any properties for which the database was generating values. Marking properties as generated, however, lets the application delegate this responsibility to Hibernate. Properties marked as generated must additionally be non-insertable and non-updateable.
Only Version and Basic types can be marked as generated. Properties like creationTimestamp fall into this category. The Generated annotation is used so that Hibernate can fetch the currently annotated property after the entity has been persisted or updated. For this reason, the Generated annotation accepts a GenerationTime enum value. When the Person entity is persisted, Hibernate is going to fetch the calculated fullName column from the database, which concatenates the first, middle, and last name.
The same goes when the Person entity is updated. Hibernate is going to fetch the calculated fullName column from the database after the entity is modified. The GeneratorType annotation is used so that you can provide a custom generator to set the value of the currently annotated property. For this reason, the GeneratorType annotation accepts a GenerationTime enum value and a custom ValueGenerator class type.
When the Person entity is persisted, Hibernate is going to populate the createdBy column with the currently logged user. Hibernate is going to populate the updatedBy column with the currently logged user. The CreationTimestamp annotation instructs Hibernate to set the annotated entity attribute with the current timestamp value of the JVM when the entity is being persisted.
When the Event entity is persisted, Hibernate is going to populate the underlying timestamp column with the current JVM timestamp value:. The UpdateTimestamp annotation instructs Hibernate to set the annotated entity attribute with the current timestamp value of the JVM when the entity is being persisted.
Hibernate 4. Generated has been retrofitted to use the ValueGenerationType meta-annotation. The actual generation logic must be added to the class that implements the AnnotationValueGeneration interface.
If the timestamp value needs to be generated in-memory, the following mapping must be used instead:. As you can see, the new Date object value was used for assigning the timestamp column value. Hibernate allows you to customize the SQL it uses to read and write the values of columns mapped to Basic types.
For example, if your database provides a set of data encryption functions, you can invoke them for individual columns like in the following example. If a property uses more than one column, you must use the forColumn attribute to specify which column the ColumnTransformer read and write expressions are targeting. Hibernate applies the custom expressions automatically whenever the property is referenced in a query. This functionality is similar to a derived-property Formula with two differences:.
The property is backed by one or more columns that are exported as part of automatic schema generation. The write expression, if specified, must contain exactly one '?
Sometimes, you want the Database to do some computation for you rather than in the JVM, you might also create some kind of virtual column. You can use a SQL fragment aka formula instead of mapping a property into a column. This kind of property is read-only its value is calculated by your formula fragment. You should be aware that the Formula annotation takes a native SQL clause which may affect database portability.
When loading the Account entity, Hibernate is going to calculate the interest property using the configured Formula :. The SQL fragment defined by the Formula annotation can be as complex as you want, and it can even include subselects. Historically Hibernate called these components. JPA calls them embeddables. Either way, the concept is the same: a composition of values. For example, we might have a Publisher class that is a composition of name and country , or a Location class that is a composition of country and city.
To avoid any confusion with the annotation that marks a given embeddable type, the annotation will be further referred to as Embeddable. Throughout this chapter and thereafter, for brevity sake, embeddable types may also be referred to as embeddable.
An embeddable type is another form of a value type, and its lifecycle is bound to a parent entity type, therefore inheriting the attribute access from its parent for details on attribute access, see Access strategies. Embeddable types can be made up of basic values as well as associations, with the caveat that, when used as collection elements, they cannot define collections themselves.
Most often, embeddable types are used to group multiple basic type mappings and reuse them across several entities. JPA defines two terms for working with an embeddable type: Embeddable and Embedded. Embeddable is used to describe the mapping type itself e. Embedded is for referencing a given embeddable type e. So, the embeddable type is represented by the Publisher class and the parent entity makes use of it through the book publisher object composition.
The composed values are mapped to the same table as the parent table. Composition is part of good object-oriented data modeling idiomatic Java. In fact, that table could also be mapped by the following entity type instead. The composition form is certainly more object-oriented, and that becomes more evident as we work with multiple embeddable types. When the same embeddable type is included multiple times in the same parent entity type, the JPA specification demands to set the associated column names explicitly.
This requirement is due to how object properties are mapped to database columns. By default, JPA expects a database column having the same name with its associated object property.
JPA defines the AttributeOverride annotation to handle this scenario. This way, the mapping conflict is resolved by setting up explicit name-based property-column type mappings. If an Embeddable type is used multiple times in some entity, you need to use the AttributeOverride and AssociationOverride annotations to override the default column names defined by the Embeddable.
Considering you have the following Publisher embeddable type which defines a ManyToOne association with the Country entity:. Now, if you have a Book entity which declares two Publisher embeddable types for the ebook and paperback versions, you cannot use the default Publisher embeddable mapping since there will be a conflict between the two embeddable column mappings. Therefore, the Book entity needs to override the embeddable type mappings for each Publisher attribute:.
Users concerned with JPA provider portability should instead prefer explicit column naming with AttributeOverride. Hibernate naming strategies are covered in detail in Naming. However, for the purposes of this discussion, Hibernate has the capability to interpret implicit column names in a way that is safe for use with multiple embeddable types. Collections of embeddable types are specifically valued collections as embeddable types are value types. Value collections are covered in detail in Collections of value types.
Embeddable types can also be used as Map keys. This topic is converted in detail in Map - key. Embeddable types can also be used as entity type identifiers. This usage is covered in detail in Composite identifiers. Embeddable types that are used as collection entries, map keys or entity type identifiers cannot include their own collection mappings.
The Target annotation is used to specify the implementation class of a given association that is mapped via an interface. The ElementCollection association has a targetClass attribute for the same purpose. However, for simple embeddable types, there is no such construct and so you need to use the Hibernate-specific Target annotation instead. The coordinates embeddable type is mapped as the Coordinates interface.
However, Hibernate needs to know the actual implementation tye, which is GPS in this case, hence the Target annotation is used to provide this information. When fetching the City entity, the coordinates property is mapped by the Target expression:. Therefore, the Target annotation is used to define a custom join association between the parent-child association.
The Hibernate-specific Parent annotation allows you to reference the owner entity from within an embeddable. When fetching the City entity, the city property of the embeddable type acts as a back reference to the owning parent entity:.
Therefore, the Parent annotation is used to define the association between an embeddable type and the owning entity.
The entity type describes the mapping between the actual persistable domain model object and a database table row. To avoid any confusion with the annotation that marks a given entity type, the annotation will be further referred to as Entity. Throughout this chapter and thereafter, entity types will be simply referred to as entity. Section 2. Applications that wish to remain portable across JPA providers should adhere to these requirements:. The entity class must be annotated with the javax.
Entity annotation or be denoted as such in XML mapping. The entity class must have a public or protected no-argument constructor. It may define additional constructors as well.
The entity class must not be final. No methods or persistent instance variables of the entity class may be final. If an entity instance is to be used remotely as a detached object, the entity class must implement the Serializable interface.
Both abstract and concrete classes can be entities. Entities may extend non-entity classes as well as entity classes, and non-entity classes may extend entity classes. The persistent state of an entity is represented by instance variables, which may correspond to JavaBean-style properties.
An instance variable must be directly accessed only from within the methods of the entity by the entity instance itself. Hibernate, however, is not as strict in its requirements. The differences from the list above include:. The entity class must have a no-argument constructor, which may be public, protected or package visibility. However, it is generally not a good idea as doing so will stop Hibernate from being able to generate proxies for lazy-loading the entity.
Hibernate does not restrict the application developer from exposing instance variables and referencing them from outside the entity class itself. The validity of such a paradigm, however, is debatable at best. A central feature of Hibernate is the ability to load lazily certain entity instance variables attributes via runtime proxies. You can still persist final classes that do not implement such an interface with Hibernate, but you will not be able to use proxies for fetching lazy associations, therefore limiting your options for performance tuning.
For the very same reason, you should also avoid declaring persistent attribute getters and setters as final. Starting with 5. Hibernate had some bytecode re-writing capabilities prior to 5. JPA requires that this constructor be defined as public or protected. Hibernate, for the most part, does not care about the constructor visibility, as long as the system SecurityManager allows overriding the visibility setting.
That said, the constructor should be defined with at least package visibility if you wish to leverage runtime proxy generation. The JPA specification requires this, otherwise, the model would prevent accessing the entity persistent state fields directly from outside the entity itself.
Although Hibernate does not require it, it is recommended to follow the JavaBean conventions and define getters and setters for entity persistent attributes. Nevertheless, you can still tell Hibernate to directly access the entity fields. Hibernate can deal with attributes declared with the public, protected, package or private visibility. However, not defining identifier attributes on the entity should be considered a deprecated feature that will be removed in an upcoming release.
The identifier attribute does not necessarily need to be mapped to the column s that physically define the primary key. However, it should map to column s that can uniquely identify each row. We recommend that you declare consistently-named identifier attributes on persistent classes and that you use a wrapper i. Long or Integer. The placement of the Id annotation marks the persistence state access strategy.
Hibernate offers multiple identifier generation strategies, see the Identifier Generators chapter for more about this topic. The main piece in mapping the entity is the javax. Entity annotation. The Entity annotation defines just the name attribute which is used to give a specific entity name for use in JPQL queries.
By default, if the name attribute of the Entity annotation is missing, the unqualified name of the entity class itself will be used as the entity name. Because the entity name is given by the unqualified name of the class, Hibernate does not allow registering multiple entities with the same name even if the entity classes reside in different packages. Without imposing this restriction, Hibernate would not know which entity class is referenced in a JPQL query if the unqualified entity name is associated with more then one entity classes.
In the following example, the entity name e. Book is given by the unqualified name of the entity class name. An entity models a database table.
The identifier uniquely identifies each row in that table. By default, the name of the table is assumed to be the same as the name of the entity. To explicitly give the name of the table or to specify other information about the table, we would use the javax.
Table annotation. Without specifying the catalog of the associated database table a given entity is mapped to, Hibernate will use the default catalog associated with the current database connection. However, if your database hosts multiple catalogs, you can specify the catalog where a given table is located using the catalog attribute of the JPA Table annotation. Now, to map the Book entity to the book table in the public catalog we can use the catalog attribute of the Table JPA annotation.
Without specifying the schema of the associated database table a given entity is mapped to, Hibernate will use the default schema associated with the current database connection. However, if your database supports schemas, you can specify the schema where a given table is located using the schema attribute of the JPA Table annotation.
Now, to map the Book entity to the book table in the library schema we can use the schema attribute of the Table JPA annotation. The schema attribute of the Table annotation works only if the underlying database supports schemas e. Much of the discussion in this section deals with the relation of an entity to a Hibernate Session, whether the entity is managed, transient or detached. If you are unfamiliar with these topics, they are explained in the Persistence Context chapter.
Whether to implement equals and hashCode methods in your domain model, let alone how to implement them, is a surprisingly tricky discussion when it comes to ORM. Generally, this is pertinent for user-defined classes used as composite identifiers. This is generally what you want in ordinary Java programming.
Conceptually, however, this starts to break down when you start to think about the possibility of multiple instances of a class representing the same data. This is, in fact, exactly the case when dealing with data coming from a database. Every time we load a specific Person from the database we would naturally get a unique instance. Hibernate, however, works hard to make sure that does not happen within a given Session. In fact, Hibernate guarantees equivalence of persistent identity database row and Java identity inside a particular session scope.
So if we ask a Hibernate Session to load that specific Person multiple times we will actually get back the same instance :. Consider we have a Library parent entity which contains a java. Set of Book entities:.
It turns out that this still breaks when adding transient instance of Book to a set as we saw in the last example:. Note that this is just a concern when using generated identifiers. If you are using assigned identifiers this will not be a problem, assuming the identifier value is assigned prior to adding to the Set. Another option is to force the identifier to be generated and set prior to adding to the Set :.
Although using a natural-id is best for equals and hashCode , sometimes you only have the entity identifier that provides a unique constraint. You can map an entity to a SQL query using the Subselect annotation.
In the example above, the Account entity does not retain any balance since every account operation is registered as an AccountTransaction. To find the Account balance, we need to query the AccountSummary which shares the same identifier with the Account entity. So, if we have the following AccountTransaction record, the AccountSummary balance will match the proper amount of money in this Account.
If we add a new AccountTransaction entity and refresh the AccountSummary entity, the balance is updated accordingly:. The goal of the Synchronize annotation in the AccountSummary entity mapping is to instruct Hibernate which database tables are needed by the underlying Subselect SQL query.
However, if the entity class is final, Javassist will not create a proxy and you will get a POJO even when you only need a proxy reference. In this case, you could proxy an interface that this particular entity implements, as illustrated by the following example.
The Proxy annotation is used to specify a custom proxy implementation for the current annotated entity. When loading the Book entity proxy, Hibernate is going to proxy the Identifiable interface instead as illustrated by the following example:.
It is possible to map your entities as dynamic proxies using the Tuplizer annotation. In the following entity mapping, both the embeddable and the entity are mapped as interfaces, not POJOs.
The Tuplizer instructs Hibernate to use the DynamicEntityTuplizer and DynamicEmbeddableTuplizer to handle the associated entity and embeddable object types. Both the Cuisine entity and the Country embeddable types are going to be instantiated as Java dynamic proxies, as you can see in the following DynamicInstantiator example:. The Persister annotation is used to specify a custom entity or collection persister. For entities, the custom persister must implement the EntityPersister interface. For collections, the custom persister must implement the CollectionPersister interface.
By providing your own EntityPersister and CollectionPersister implementations, you can control how entities and collections are persisted into the database. As a JPA provider, Hibernate can introspect both the entity attributes instance fields or the accessors instance properties. By default, the placement of the Id annotation gives the default access strategy.
When placed on a field, Hibernate will assume field-based access. When placed on the identifier getter, Hibernate will use property-based access.
To avoid issues such as HCANN - Property name beginning with at least two uppercase characters has odd functionality in HQL , you should pay attention to Java Bean specification in regard to naming properties. To exclude a field from being part of the entity persistent state, the field must be marked with the Transient annotation.
Another advantage of using field-based access is that some entity attributes can be hidden from outside the entity. An example of such attribute is the entity Version field, which, usually, does not need to be manipulated by the data access layer.
With field-based access, we can simply omit the getter and the setter for this version field, and Hibernate can still leverage the optimistic concurrency control mechanism. When using property-based access, Hibernate uses the accessors for both reading and writing the entity state. Every other method that will be added to the entity e. The default access strategy mechanism can be overridden with the JPA Access annotation.
In the following example, the Version attribute is accessed by its field and not by its getter, like the rest of entity attributes. Because embeddables are managed by their owning entities, the access strategy is therefore inherited from the entity too. This applies to both simple embeddable types as well as for collection of embeddables.
The embeddable types can overrule the default implicit access strategy inherited from the owning entity. In the following example, the embeddable uses property-based access, no matter what access strategy the owning entity is choosing:. The owning entity can use field-based access while the embeddable uses property-based access as it has chosen explicitly:.
Identifiers model the primary key of an entity. They are used to uniquely identify each specific entity. Hibernate and JPA both make the following assumptions about the corresponding database column s :. The values, once inserted, can never be changed. This is more a general guide, than a hard-fast rule as opinions vary.
JPA defines the behavior of changing the value of the identifier attribute to be undefined; Hibernate simply does not support that.
In cases where the values for the PK you have chosen will be updated, Hibernate recommends mapping the mutable value as a natural id, and use a surrogate id for the PK.
See Natural Ids. Technically the identifier does not have to map to the column s physically defined as the table primary key. They just need to map to column s that uniquely identify each row.
However, this documentation will continue to use the terms identifier and primary key interchangeably. Every entity must define an identifier. For entity inheritance hierarchies, the identifier must be defined just on the entity that is the root of the hierarchy. Simple identifiers map to a single basic attribute, and are denoted using the javax.
Id annotation. Values for simple identifiers can be assigned, as we have seen in the examples above. Values for simple identifiers can be generated. To denote that an identifier attribute is generated, it is annotated with javax.
Additionally, to the type restriction list above, JPA says that if using generated identifier values see below only integer types short, int, long will be portably supported. Identifier value generations strategies are discussed in detail in the Generated identifier values section. Composite identifiers correspond to one or more persistent attributes. Here are the rules governing composite identifiers, as defined by the JPA specification:. The composite identifier must be represented by a "primary key class".
The primary key class may be defined using the javax. EmbeddedId annotation see Composite identifiers with EmbeddedId , or defined using the javax. IdClass annotation see Composite identifiers with IdClass. The primary key class must define equals and hashCode methods, consistent with equality for the underlying database types to which the primary key is mapped.
The restriction that a composite identifier has to be represented by a "primary key class" e. Hibernate does allow composite identifiers to be defined without a "primary key class" via multiple Id attributes. The attributes making up the composition can be either basic, composite, ManyToOne. Note especially that collection and one-to-one are never appropriate. Modeling a composite identifier using an EmbeddedId simply means defining an embeddable to be a composition for the one or more attributes making up the identifier, and then exposing an attribute of that embeddable type on the entity.
However, that is not portably supported by the JPA specification. In JPA terms, one would use "derived identifiers". For more details, see Derived Identifiers. Modeling a composite identifier using an IdClass differs from using an EmbeddedId in that the entity defines each individual attribute making up the composition.
The IdClass simply acts as a "shadow". Non-aggregated composite identifiers can also contain ManyToOne attributes as we saw with aggregated ones still non-portably.
With non-aggregated composite identifiers, Hibernate also supports "partial" generation of the composite values.
This feature which allows auto-generated values in composite identifiers exists because of a highly questionable interpretation of the JPA specification made by the SpecJ committee.
Hibernate does not feel that JPA defines support for this, but added the feature simply to be usable in SpecJ benchmarks. Use of this feature may or may not be portable from a JPA perspective. Hibernate allows defining a composite identifier out of entity associations. In the following example, the PersonAddress entity identifier is formed of two ManyToOne associations. To query this entity, an instance of the entity itself must be supplied to the persistence context.
When using composite identifiers, the underlying identifier properties must be manually assigned by the user. Automatically generated properties are not supported to be used to generate the value of an underlying property that makes the composite identifier. Therefore, you cannot use any of the automatic property generator described by the generated properties section like Generated , CreationTimestamp or ValueGenerationType or database-generated values.
Nevertheless, you can still generate the identifier properties prior to constructing the composite identifier, as illustrated by the following examples. Assuming we have the following EventId composite identifier and an Event entity which uses the aforementioned composite identifier. If you want to generate the composite identifier properties in-memory, you need to do that as follows:.
Notice that the createdOn property of the EventId composite identifier was generated by the data access code and assigned to the identifier prior to persisting the Event entity. If you want to generate the composite identifier properties using a database function or stored procedure, you could to do it as illustrated by the following example.
You can also auto-generate values for non-identifier attributes. For more details, see the Generated properties section. Hibernate supports identifier value generation across a number of different types. Remember that JPA portably defines identifier value generation just for integer types. Identifier value generation is indicated using the javax. GeneratedValue annotation. The most important piece of information here is the specified javax.
GenerationType which indicates how values will be generated. Starting with Hibernate 5, this is set to true by default. In applications where the hibernate. The rest of the discussion here assumes this setting is enabled true. In Hibernate 5. We wanted to restore the behavior prior to 5. Entity mappings can sometimes be complex and it is possible a corner case was overlooked. Hibernate offers a way to completely disable the 5. To enable the legacy behavior, set hibernate. This configuration option is meant to act as a temporary fix and bridge the gap between the changes in this behavior across Hibernate 5.
If this configuration setting is necessary for a mapping, please open a JIRA and report the mapping so that the algorithm can be reviewed. Indicates that the persistence provider Hibernate should choose an appropriate generation strategy. Indicates that database sequence should be used for obtaining primary key values.
See Using sequences. Indicates that a database table should be used for obtaining primary key values. See Using the table identifier generator. If the identifier type is numerical e. Long , Integer , then Hibernate is going to use the IdGeneratorStrategyInterpreter to resolve the identifier generator strategy. The IdGeneratorStrategyInterpreter has two implementations:. This is the default strategy since Hibernate 5.
For older versions, this strategy is enabled through the hibernate. This is a legacy mechanism that was used by Hibernate prior to version 5. The legacy strategy maps AUTO to the native generator strategy which uses the Dialect getNativeIdentifierGeneratorStrategy to resolve the actual identifier generator e.
For implementing database sequence-based identifier value generation Hibernate makes use of its org. SequenceStyleGenerator id generator. It is important to note that SequenceStyleGenerator is capable of working against databases that do not support sequences by switching to a table as the underlying backing. This backing storage is completely transparent to the user. The preferred and portable way to configure this generator is using the JPA-defined javax.
SequenceGenerator annotation. Using javax. SequenceGenerator , you can specify a specific database sequence name. The javax.
SequenceGenerator annotation allows you to specify additional configurations as well. It is important to realize that using IDENTITY columns imposes a runtime behavior where the entity row must be physically inserted prior to the identifier value being known.
This can mess up extended persistence contexts long conversations. The importance of this depends on the application-specific use cases. If the application is not usually creating many new instances of a given entity type using the IDENTITY generator, then this limitation will be less important since batching would not have been very helpful anyway.
Hibernate achieves table-based identifier generation based on its org. TableGenerator which defines a table capable of holding multiple named value segments for any number of entities. Additionally, because no javax. However, you can configure the table identifier generator using the TableGenerator annotation.
Now, when inserting 3 Product entities, Hibernate generates the following statements:. This is supported through its org. UUIDGenerator id generator. These strategies are defined by the org. Hibernate does ship with an alternative strategy which is a RFC version 1 time-based strategy using IP address rather than mac address.
Here we choose the RFC version 1 compliant strategy named org. Most of the Hibernate generators that separately obtain identifier values from database structures support the use of pluggable optimizers. Optimizers help manage the number of times Hibernate has to talk to the database in order to generate identifier values. For example, with no optimizer applied to a sequence-generator, every time the application asked Hibernate to generate an identifier it would need to grab the next sequence value from the database.
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