How to generate the JPA entity Metamodel?

2023-01-03 14:38 问答作者：

In the spirit of type safety associated with the CriteriaQuery JPA 2.0 also has an API to support Metamodel representation of entities.

Is anyone aware of a fully functional implementation of this API (to generate the Metamodel as opposed to creating the metamodel classes manually)? It would be awesome if someone also knows the steps for setting this up in Eclipse (I assume it's as simple as setting up an annotation processor, but you never know).

EDIT: Just stumbled across Hibernate JPA 2 Metamodel Generator . But the issue remains since I can't fin开发者_Go百科d any download links for the jar.

EDIT 2: Awhile has passed since I asked this question, but I thought I'd come back and add a link to the Hibernate JPA Model Generator project on SourceForge

It would be awesome if someone also knows the steps for setting this up in Eclipse (I assume it's as simple as setting up an annotation processor, but you never know)

Yes it is. Here are the implementations and instructions for the various JPA 2.0 implementations:

EclipseLink

org.eclipse.persistence.internal.jpa.modelgen.CanonicalModelProcessor

Hibernate

org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor
http://in.relation.to/2009/11/09/hibernate-static-metamodel-generator-annotation-processor

OpenJPA

org.apache.openjpa.persistence.meta.AnnotationProcessor6
http://openjpa.apache.org/builds/2.4.1/apache-openjpa/docs/ch13s04.html

DataNucleus

org.datanucleus.jpa.JPACriteriaProcessor
http://www.datanucleus.org/products/accessplatform_2_1/jpa/jpql_criteria_metamodel.html

The latest Hibernate implementation is available at:

https://mvnrepository.com/artifact/org.hibernate/hibernate-jpamodelgen/

An older Hibernate implementation is at:

http://repository.jboss.com/maven2/org/hibernate/hibernate-jpamodelgen/1.0.0.Final/hibernate-jpamodelgen-1.0.0.Final.jar

Please take a look at jpa-metamodels-with-maven-example.

Hibernate

We need org.hibernate.org:hibernate-jpamodelgen.
The processor class is org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor.

Hibernate as a dependency

    <dependency>
      <groupId>org.hibernate.orm</groupId>
      <artifactId>hibernate-jpamodelgen</artifactId>
      <version>${version.hibernate-jpamodelgen}</version>
      <scope>provided</scope>
    </dependency>

Hibernate as a processor

      <plugin>
        <groupId>org.bsc.maven</groupId>
        <artifactId>maven-processor-plugin</artifactId>
        <executions>
          <execution>
            <goals>
              <goal>process</goal>
            </goals>
            <phase>generate-sources</phase>
            <configuration>
              <compilerArguments>-AaddGeneratedAnnotation=false</compilerArguments> <!-- suppress java.annotation -->
              <processors>
                <processor>org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor</processor>
              </processors>
            </configuration>
          </execution>
        </executions>
        <dependencies>
          <dependency>
            <groupId>org.hibernate.orm</groupId>
            <artifactId>hibernate-jpamodelgen</artifactId>
            <version>${version.hibernate-jpamodelgen}</version>
          </dependency>
        </dependencies>
      </plugin>

OpenJPA

We need org.apache.openjpa:openjpa.
The processor class is org.apache.openjpa.persistence.meta.AnnotationProcessor6.
OpenJPA seems require additional element <openjpa.metamodel>true<openjpa.metamodel>.

OpenJPA as a dependency

  <dependencies>
    <dependency>
      <groupId>org.apache.openjpa</groupId>
      <artifactId>openjpa</artifactId>
      <scope>provided</scope>
    </dependency>
  </dependencies>
  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <configuration>
          <compilerArgs>
            <arg>-Aopenjpa.metamodel=true</arg>
          </compilerArgs>
        </configuration>
      </plugin>
    </plugins>
  </build>

OpenJPA as a processor

      <plugin>
        <groupId>org.bsc.maven</groupId>
        <artifactId>maven-processor-plugin</artifactId>
        <executions>
          <execution>
            <id>process</id>
            <goals>
              <goal>process</goal>
            </goals>
            <phase>generate-sources</phase>
            <configuration>
              <processors>
                <processor>org.apache.openjpa.persistence.meta.AnnotationProcessor6</processor>
              </processors>
              <optionMap>
                <openjpa.metamodel>true</openjpa.metamodel>
              </optionMap>
            </configuration>
          </execution>
        </executions>
        <dependencies>
          <dependency>
            <groupId>org.apache.openjpa</groupId>
            <artifactId>openjpa</artifactId>
            <version>${version.openjpa}</version>
          </dependency>
        </dependencies>
      </plugin>

EclipseLink

We need org.eclipse.persistence:org.eclipse.persistence.jpa.modelgen.processor.
The processor class is org.eclipse.persistence.internal.jpa.modelgen.CanonicalModelProcessor.
EclipseLink requires persistence.xml.

EclipseLink as a dependency

  <dependencies>
    <dependency>
      <groupId>org.eclipse.persistence</groupId>
      <artifactId>org.eclipse.persistence.jpa.modelgen.processor</artifactId>
      <scope>provided</scope>
    </dependency>

EclipseLink as a processor

    <plugins>
      <plugin>
        <groupId>org.bsc.maven</groupId>
        <artifactId>maven-processor-plugin</artifactId>
        <executions>
          <execution>
            <goals>
              <goal>process</goal>
            </goals>
            <phase>generate-sources</phase>
            <configuration>
              <processors>
                <processor>org.eclipse.persistence.internal.jpa.modelgen.CanonicalModelProcessor</processor>
              </processors>
              <compilerArguments>-Aeclipselink.persistencexml=src/main/resources-${environment.id}/META-INF/persistence.xml</compilerArguments>
            </configuration>
          </execution>
        </executions>
        <dependencies>
          <dependency>
            <groupId>org.eclipse.persistence</groupId>
            <artifactId>org.eclipse.persistence.jpa.modelgen.processor</artifactId>
            <version>${version.eclipselink}</version>
          </dependency>
        </dependencies>
      </plugin>

DataNucleus

We need org.datanucleus:datanucleus-jpa-query.
The processor class is org.datanucleus.jpa.query.JPACriteriaProcessor.

DataNucleus as a dependency

  <dependencies>
    <dependency>
      <groupId>org.datanucleus</groupId>
      <artifactId>datanucleus-jpa-query</artifactId>
      <scope>provided</scope>
    </dependency>
  </dependencies>

DataNucleus as a processor

      <plugin>
        <groupId>org.bsc.maven</groupId>
        <artifactId>maven-processor-plugin</artifactId>
        <executions>
          <execution>
            <id>process</id>
            <goals>
              <goal>process</goal>
            </goals>
            <phase>generate-sources</phase>
            <configuration>
              <processors>
                <processor>org.datanucleus.jpa.query.JPACriteriaProcessor</processor>
              </processors>
            </configuration>
          </execution>
        </executions>
        <dependencies>
          <dependency>
            <groupId>org.datanucleus</groupId>
            <artifactId>datanucleus-jpa-query</artifactId>
            <version>${version.datanucleus}</version>
          </dependency>
        </dependencies>
      </plugin>

Eclipse's JPA 2.0 support through Dali (which is included in "Eclipse IDE for JEE Developers") has its own metamodel generator integrated with Eclipse.

Select your project in the Package Explorer
Go to Properties -> JPA dialog
Select source folder from Canonical metamodel (JPA 2.0) group
Click Apply button to generate metamodel classes in the selected source folder

How to generate the JPA entity Metamodel?

This should work on any JPA provider as the generated classes are standard.

Also see here.

Let's assume our application uses the following Post, PostComment, PostDetails, and Tag entities, which form a one-to-many, one-to-one, and many-to-many table relationships:

How to generate the JPA entity Metamodel?

How to generate the JPA Criteria Metamodel

The hibernate-jpamodelgen tool provided by Hibernate ORM can be used to scan the project entities and generate the JPA Criteria Metamodel. All you need to do is add the following annotationProcessorPath to the maven-compiler-plugin in the Maven pom.xml configuration file:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>${maven-compiler-plugin.version}</version>
    <configuration>
        <annotationProcessorPaths>
            <annotationProcessorPath>
                <groupId>org.hibernate</groupId>
                <artifactId>hibernate-jpamodelgen</artifactId>
                <version>${hibernate.version}</version>
            </annotationProcessorPath>
        </annotationProcessorPaths>
    </configuration>
</plugin>

Now, when the project is compiled, you can see that in the target folder, the following Java classes are generated:

> tree target/generated-sources/
target/generated-sources/
└── annotations
    └── com
        └── vladmihalcea
            └── book
                └── hpjp
                    └── hibernate
                        ├── forum
                        │   ├── PostComment_.java
                        │   ├── PostDetails_.java
                        │   ├── Post_.java
                        │   └── Tag_.java

Tag entity Metamodel

If the Tag entity is mapped as follows:

@Entity
@Table(name = "tag")
public class Tag {

    @Id
    private Long id;

    private String name;

    //Getters and setters omitted for brevity
}

The Tag_ Metamodel class is generated like this:

@Generated(value = "org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor")
@StaticMetamodel(Tag.class)
public abstract class Tag_ {

    public static volatile SingularAttribute<Tag, String> name;
    public static volatile SingularAttribute<Tag, Long> id;

    public static final String NAME = "name";
    public static final String ID = "id";
}

The SingularAttribute is used for the basic id and name Tag JPA entity attributes.

Post entity Metamodel

The Post entity is mapped like this:

@Entity
@Table(name = "post")
public class Post {

    @Id
    private Long id;

    private String title;

    @OneToMany(
        mappedBy = "post",
        cascade = CascadeType.ALL,
        orphanRemoval = true
    )
    private List<PostComment> comments = new ArrayList<>();

    @OneToOne(
        mappedBy = "post",
        cascade = CascadeType.ALL,
        fetch = FetchType.LAZY
    )
    @LazyToOne(LazyToOneOption.NO_PROXY)
    private PostDetails details;

    @ManyToMany
    @JoinTable(
        name = "post_tag",
        joinColumns = @JoinColumn(name = "post_id"),
        inverseJoinColumns = @JoinColumn(name = "tag_id")
    )
    private List<Tag> tags = new ArrayList<>();
    
    //Getters and setters omitted for brevity
}

The Post entity has two basic attributes, id and title, a one-to-many comments collection, a one-to-one details association, and a many-to-many tags collection.

The Post_ Metamodel class is generated as follows:

@Generated(value = "org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor")
@StaticMetamodel(Post.class)
public abstract class Post_ {

    public static volatile ListAttribute<Post, PostComment> comments;
    public static volatile SingularAttribute<Post, PostDetails> details;
    public static volatile SingularAttribute<Post, Long> id;
    public static volatile SingularAttribute<Post, String> title;
    public static volatile ListAttribute<Post, Tag> tags;

    public static final String COMMENTS = "comments";
    public static final String DETAILS = "details";
    public static final String ID = "id";
    public static final String TITLE = "title";
    public static final String TAGS = "tags";
}

The basic id and title attributes, as well as the one-to-one details association, are represented by a SingularAttribute while the comments and tags collections are represented by the JPA ListAttribute.

PostDetails entity Metamodel

The PostDetails entity is mapped like this:

@Entity
@Table(name = "post_details")
public class PostDetails {

    @Id
    @GeneratedValue
    private Long id;

    @Column(name = "created_on")
    private Date createdOn;

    @Column(name = "created_by")
    private String createdBy;

    @OneToOne(fetch = FetchType.LAZY)
    @MapsId
    @JoinColumn(name = "id")
    private Post post;
    
    //Getters and setters omitted for brevity
}

All entity attributes are going to be represented by the JPA SingularAttribute in the associated PostDetails_ Metamodel class:

@Generated(value = "org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor")
@StaticMetamodel(PostDetails.class)
public abstract class PostDetails_ {

    public static volatile SingularAttribute<PostDetails, Post> post;
    public static volatile SingularAttribute<PostDetails, String> createdBy;
    public static volatile SingularAttribute<PostDetails, Long> id;
    public static volatile SingularAttribute<PostDetails, Date> createdOn;

    public static final String POST = "post";
    public static final String CREATED_BY = "createdBy";
    public static final String ID = "id";
    public static final String CREATED_ON = "createdOn";
}

PostComment entity Metamodel

The PostComment is mapped as follows:

@Entity
@Table(name = "post_comment")
public class PostComment {

    @Id
    private Long id;

    @ManyToOne(fetch = FetchType.LAZY)
    private Post post;

    private String review;
    
    //Getters and setters omitted for brevity
}

And, all entity attributes are represented by the JPA SingularAttribute in the associated PostComments_ Metamodel class:

@Generated(value = "org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor")
@StaticMetamodel(PostComment.class)
public abstract class PostComment_ {

    public static volatile SingularAttribute<PostComment, Post> post;
    public static volatile SingularAttribute<PostComment, String> review;
    public static volatile SingularAttribute<PostComment, Long> id;

    public static final String POST = "post";
    public static final String REVIEW = "review";
    public static final String ID = "id";
}

Using the JPA Criteria Metamodel

Without the JPA Metamodel, a Criteria API query that needs to fetch the PostComment entities filtered by their associated Post title would look like this:

CriteriaBuilder builder = entityManager.getCriteriaBuilder();

CriteriaQuery<PostComment> query = builder.createQuery(PostComment.class);
Root<PostComment> postComment = query.from(PostComment.class);

Join<PostComment, Post> post = postComment.join("post");

query.where(
    builder.equal(
        post.get("title"),
        "High-Performance Java Persistence"
    )
);

List<PostComment> comments = entityManager
    .createQuery(query)
    .getResultList();

Notice that we used the post String literal when creating the Join instance, and we used the title String literal when referencing the Post title.

The JPA Metamodel allows us to avoid hard-coding entity attributes, as illustrated by the following example:

CriteriaBuilder builder = entityManager.getCriteriaBuilder();

CriteriaQuery<PostComment> query = builder.createQuery(PostComment.class);
Root<PostComment> postComment = query.from(PostComment.class);

Join<PostComment, Post> post = postComment.join(PostComment_.post);

query.where(
    builder.equal(
        post.get(Post_.title),
        "High-Performance Java Persistence"
    )
);

List<PostComment> comments = entityManager
    .createQuery(query)
    .getResultList();

Or, let's say we want to fetch a DTO projection while filtering the Post title and the PostDetails createdOn attributes.

We can use the Metamodel when creating the join attributes, as well as when building the DTO projection column aliases or when referencing the entity attributes we need to filter:

CriteriaBuilder builder = entityManager.getCriteriaBuilder();

CriteriaQuery<Object[]> query = builder.createQuery(Object[].class);

Root<PostComment> postComment = query.from(PostComment.class);
Join<PostComment, Post> post = postComment.join(PostComment_.post);

query.multiselect(
    postComment.get(PostComment_.id).alias(PostComment_.ID),
    postComment.get(PostComment_.review).alias(PostComment_.REVIEW),
    post.get(Post_.title).alias(Post_.TITLE)
);

query.where(
    builder.and(
        builder.like(
            post.get(Post_.title),
            "%Java Persistence%"
        ),
        builder.equal(
            post.get(Post_.details).get(PostDetails_.CREATED_BY),
            "Vlad Mihalcea"
        )
    )
);

List<PostCommentSummary> comments = entityManager
    .createQuery(query)
    .unwrap(Query.class)
    .setResultTransformer(Transformers.aliasToBean(PostCommentSummary.class))
    .getResultList();

Cool, right?

For eclipselink, only the following dependency is sufficient to generate metamodel. Nothing else is needed.

    <dependency>
        <groupId>org.eclipse.persistence</groupId>
        <artifactId>org.eclipse.persistence.jpa.modelgen.processor</artifactId>
        <version>2.5.1</version>
        <scope>provided</scope>
    </dependency>

For Hibernate as provider which is most common IMHO:

In case of build tools like Gradle, Maven you need to have Hibernate JPA 2 Metamodel Generator jar in the classpath and compiler level>=1.6 that is all you need build the project and metamodel will be generated automatically.

In case of IDE Eclipse 1. goto Project->Properties->Java Compiler->Annotation Processing and enable it. 2. Expand Annotation Processing->Factory Path-> Add External Jar add Hibernate JPA 2 Metamodel Generator jar check the newly added jar and say OK. Clean and Build done!

Link Hibernate JPA 2 Metamodel Generator jar link from maven repo https://mvnrepository.com/artifact/org.hibernate/hibernate-jpamodelgen

Ok, based on what I have read here, I did it with EclipseLink this way and I did not need to put the processor dependency to the project, only as an annotationProcessorPath element of the compiler plugin.

    <plugin>
        <artifactId>maven-compiler-plugin</artifactId>
        <configuration>
            <annotationProcessorPaths>
                <annotationProcessorPath>
                    <groupId>org.eclipse.persistence</groupId>
                    <artifactId>org.eclipse.persistence.jpa.modelgen.processor</artifactId>
                    <version>2.7.7</version>
                </annotationProcessorPath>
            </annotationProcessorPaths>
            <compilerArgs>
                <arg>-Aeclipselink.persistencexml=src/main/resources/META-INF/persistence.xml</arg>
            </compilerArgs>
        </configuration>
    </plugin>

See this post for a minimal configuration with maven and how to deal with generated JPA metamodel source code in IDEs.

继续阅读：annotation-processing jpa metamodel

How to generate the JPA entity Metamodel?

EclipseLink

Hibernate

OpenJPA

DataNucleus

Hibernate

Hibernate as a dependency

Hibernate as a processor

OpenJPA

OpenJPA as a dependency

OpenJPA as a processor

EclipseLink

EclipseLink as a dependency

EclipseLink as a processor

DataNucleus

DataNucleus as a dependency

DataNucleus as a processor

How to generate the JPA Criteria Metamodel

Tag entity Metamodel

Post entity Metamodel

PostDetails entity Metamodel

PostComment entity Metamodel

Using the JPA Criteria Metamodel

更多精彩内容

精彩评论

最新问答

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imessage会显示已读吗？

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EclipseLink

Hibernate

OpenJPA

DataNucleus

Hibernate

Hibernate as a dependency

Hibernate as a processor

OpenJPA

OpenJPA as a dependency

OpenJPA as a processor

EclipseLink

EclipseLink as a dependency

EclipseLink as a processor

DataNucleus

DataNucleus as a dependency

DataNucleus as a processor

How to generate the JPA Criteria Metamodel

Tag entity Metamodel

Post entity Metamodel

PostDetails entity Metamodel

PostComment entity Metamodel

Using the JPA Criteria Metamodel

更多精彩内容

精彩评论

最新问答

央视是哪个频道？

请问买过的朋友，舒提啦旅行箱实际使用体验如何？？

检查不孕不育需要的费用？

海信ULED电视画质有什么不同的地方?？

钉子可以挂的住画框幕布吗？

问答排行榜

王昌瑞《潜梦追凶》剧组庆生 新锐演员未来可期？

Is it allowed to ask users to enter credit card details for own payment method?

Escaping "<" in Perl-generated XML

imessage会显示已读吗？

微信重新建群怎么建？

王昌瑞《潜梦追凶》剧组庆生新锐演员未来可期？