How to generate the JPA entity Metamodel

Question

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 find 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

User · Answer

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     This should work on any JPA provider as the generated classes are standard   Also see here

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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       lt dependency gt         lt groupId gt org hibernate orm lt  groupId gt         lt artifactId gt hibernate-jpamodelgen lt  artifactId gt         lt version gt   version hibernate-jpamodelgen  lt  version gt         lt scope gt provided lt  scope gt       lt  dependency gt    Hibernate as a processor         lt plugin gt           lt groupId gt org bsc maven lt  groupId gt           lt artifactId gt maven-processor-plugin lt  artifactId gt           lt executions gt             lt execution gt               lt goals gt                 lt goal gt process lt  goal gt               lt  goals gt               lt phase gt generate-sources lt  phase gt               lt configuration gt                 lt compilerArguments gt -AaddGeneratedAnnotation false lt  compilerArguments gt   lt  -- suppress java annotation -- gt                 lt processors gt                   lt processor gt org hibernate jpamodelgen JPAMetaModelEntityProcessor lt  processor gt                 lt  processors gt               lt  configuration gt             lt  execution gt           lt  executions gt           lt dependencies gt             lt dependency gt               lt groupId gt org hibernate orm lt  groupId gt               lt artifactId gt hibernate-jpamodelgen lt  artifactId gt               lt version gt   version hibernate-jpamodelgen  lt  version gt             lt  dependency gt           lt  dependencies gt         lt  plugin gt    OpenJPA   We need org apache openjpa openjpa  The processor class is org apache openjpa persistence meta AnnotationProcessor6  OpenJPA seems require additional element  lt openjpa metamodel gt true lt openjpa metamodel gt     OpenJPA as a dependency     lt dependencies gt       lt dependency gt         lt groupId gt org apache openjpa lt  groupId gt         lt artifactId gt openjpa lt  artifactId gt         lt scope gt provided lt  scope gt       lt  dependency gt     lt  dependencies gt     lt build gt       lt plugins gt         lt plugin gt           lt groupId gt org apache maven plugins lt  groupId gt           lt artifactId gt maven-compiler-plugin lt  artifactId gt           lt configuration gt             lt compilerArgs gt               lt arg gt -Aopenjpa metamodel true lt  arg gt             lt  compilerArgs gt           lt  configuration gt         lt  plugin gt       lt  plugins gt     lt  build gt    OpenJPA as a processor         lt plugin gt           lt groupId gt org bsc maven lt  groupId gt           lt artifactId gt maven-processor-plugin lt  artifactId gt           lt executions gt             lt execution gt               lt id gt process lt  id gt               lt goals gt                 lt goal gt process lt  goal gt               lt  goals gt               lt phase gt generate-sources lt  phase gt               lt configuration gt                 lt processors gt                   lt processor gt org apache openjpa persistence meta AnnotationProcessor6 lt  processor gt                 lt  processors gt                 lt optionMap gt                   lt openjpa metamodel gt true lt  openjpa metamodel gt                 lt  optionMap gt               lt  configuration gt             lt  execution gt           lt  executions gt           lt dependencies gt             lt dependency gt               lt groupId gt org apache openjpa lt  groupId gt               lt artifactId gt openjpa lt  artifactId gt               lt version gt   version openjpa  lt  version gt             lt  dependency gt           lt  dependencies gt         lt  plugin gt    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     lt dependencies gt       lt dependency gt         lt groupId gt org eclipse persistence lt  groupId gt         lt artifactId gt org eclipse persistence jpa modelgen processor lt  artifactId gt         lt scope gt provided lt  scope gt       lt  dependency gt    EclipseLink as a processor       lt plugins gt         lt plugin gt           lt groupId gt org bsc maven lt  groupId gt           lt artifactId gt maven-processor-plugin lt  artifactId gt           lt executions gt             lt execution gt               lt goals gt                 lt goal gt process lt  goal gt               lt  goals gt               lt phase gt generate-sources lt  phase gt               lt configuration gt                 lt processors gt                   lt processor gt org eclipse persistence internal jpa modelgen CanonicalModelProcessor lt  processor gt                 lt  processors gt                 lt compilerArguments gt -Aeclipselink persistencexml src main resources-  environment id  META-INF persistence xml lt  compilerArguments gt               lt  configuration gt             lt  execution gt           lt  executions gt           lt dependencies gt             lt dependency gt               lt groupId gt org eclipse persistence lt  groupId gt               lt artifactId gt org eclipse persistence jpa modelgen processor lt  artifactId gt               lt version gt   version eclipselink  lt  version gt             lt  dependency gt           lt  dependencies gt         lt  plugin gt    DataNucleus   We need org datanucleus datanucleus-jpa-query  The processor class is org datanucleus jpa query JPACriteriaProcessor    DataNucleus as a dependency     lt dependencies gt       lt dependency gt         lt groupId gt org datanucleus lt  groupId gt         lt artifactId gt datanucleus-jpa-query lt  artifactId gt         lt scope gt provided lt  scope gt       lt  dependency gt     lt  dependencies gt    DataNucleus as a processor         lt plugin gt           lt groupId gt org bsc maven lt  groupId gt           lt artifactId gt maven-processor-plugin lt  artifactId gt           lt executions gt             lt execution gt               lt id gt process lt  id gt               lt goals gt                 lt goal gt process lt  goal gt               lt  goals gt               lt phase gt generate-sources lt  phase gt               lt configuration gt                 lt processors gt                   lt processor gt org datanucleus jpa query JPACriteriaProcessor lt  processor gt                 lt  processors gt               lt  configuration gt             lt  execution gt           lt  executions gt           lt dependencies gt             lt dependency gt               lt groupId gt org datanucleus lt  groupId gt               lt artifactId gt datanucleus-jpa-query lt  artifactId gt               lt version gt   version datanucleus  lt  version gt             lt  dependency gt           lt  dependencies gt         lt  plugin gt

User · Answer

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

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For eclipselink  only the following dependency is sufficient to generate metamodel  Nothing else is needed         lt dependency gt           lt groupId gt org eclipse persistence lt  groupId gt           lt artifactId gt org eclipse persistence jpa modelgen processor lt  artifactId gt           lt version gt 2 5 1 lt  version gt           lt scope gt provided lt  scope gt       lt  dependency gt

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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 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   lt plugin gt       lt groupId gt org apache maven plugins lt  groupId gt       lt artifactId gt maven-compiler-plugin lt  artifactId gt       lt version gt   maven-compiler-plugin version  lt  version gt       lt configuration gt           lt annotationProcessorPaths gt               lt annotationProcessorPath gt                   lt groupId gt org hibernate lt  groupId gt                   lt artifactId gt hibernate-jpamodelgen lt  artifactId gt                   lt version gt   hibernate version  lt  version gt               lt  annotationProcessorPath gt           lt  annotationProcessorPaths gt       lt  configuration gt   lt  plugin gt   Now  when the project is compiled  you can see that in the target folder  the following Java classes are generated   gt  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    quot tag quot   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    quot org hibernate jpamodelgen JPAMetaModelEntityProcessor quot    StaticMetamodel Tag class  public abstract class Tag         public static volatile SingularAttribute lt Tag  String gt  name      public static volatile SingularAttribute lt Tag  Long gt  id       public static final String NAME    quot name quot       public static final String ID    quot id quot      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    quot post quot   public class Post         Id     private Long id       private String title        OneToMany          mappedBy    quot post quot           cascade   CascadeType ALL          orphanRemoval   true           private List lt PostComment gt  comments   new ArrayList lt  gt           OneToOne          mappedBy    quot post quot           cascade   CascadeType ALL          fetch   FetchType LAZY            LazyToOne LazyToOneOption NO PROXY      private PostDetails details        ManyToMany      JoinTable          name    quot post tag quot           joinColumns    JoinColumn name    quot post id quot            inverseJoinColumns    JoinColumn name    quot tag id quot             private List lt Tag gt  tags   new ArrayList lt  gt                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    quot org hibernate jpamodelgen JPAMetaModelEntityProcessor quot    StaticMetamodel Post class  public abstract class Post         public static volatile ListAttribute lt Post  PostComment gt  comments      public static volatile SingularAttribute lt Post  PostDetails gt  details      public static volatile SingularAttribute lt Post  Long gt  id      public static volatile SingularAttribute lt Post  String gt  title      public static volatile ListAttribute lt Post  Tag gt  tags       public static final String COMMENTS    quot comments quot       public static final String DETAILS    quot details quot       public static final String ID    quot id quot       public static final String TITLE    quot title quot       public static final String TAGS    quot tags quot      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    quot post details quot   public class PostDetails         Id      GeneratedValue     private Long id        Column name    quot created on quot       private Date createdOn        Column name    quot created by quot       private String createdBy        OneToOne fetch   FetchType LAZY       MapsId      JoinColumn name    quot id quot       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    quot org hibernate jpamodelgen JPAMetaModelEntityProcessor quot    StaticMetamodel PostDetails class  public abstract class PostDetails         public static volatile SingularAttribute lt PostDetails  Post gt  post      public static volatile SingularAttribute lt PostDetails  String gt  createdBy      public static volatile SingularAttribute lt PostDetails  Long gt  id      public static volatile SingularAttribute lt PostDetails  Date gt  createdOn       public static final String POST    quot post quot       public static final String CREATED BY    quot createdBy quot       public static final String ID    quot id quot       public static final String CREATED ON    quot createdOn quot      PostComment entity Metamodel The PostComment is mapped as follows   Entity  Table name    quot post comment quot   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    quot org hibernate jpamodelgen JPAMetaModelEntityProcessor quot    StaticMetamodel PostComment class  public abstract class PostComment         public static volatile SingularAttribute lt PostComment  Post gt  post      public static volatile SingularAttribute lt PostComment  String gt  review      public static volatile SingularAttribute lt PostComment  Long gt  id       public static final String POST    quot post quot       public static final String REVIEW    quot review quot       public static final String ID    quot id quot      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 lt PostComment gt  query   builder createQuery PostComment class   Root lt PostComment gt  postComment   query from PostComment class    Join lt PostComment  Post gt  post   postComment join  quot post quot     query where      builder equal          post get  quot title quot             quot High-Performance Java Persistence quot            List lt PostComment gt  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 lt PostComment gt  query   builder createQuery PostComment class   Root lt PostComment gt  postComment   query from PostComment class    Join lt PostComment  Post gt  post   postComment join PostComment  post    query where      builder equal          post get Post  title            quot High-Performance Java Persistence quot            List lt PostComment gt  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 lt Object   gt  query   builder createQuery Object   class    Root lt PostComment gt  postComment   query from PostComment class   Join lt PostComment  Post gt  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                quot  Java Persistence  quot                     builder equal              post get Post  details  get PostDetails  CREATED BY                quot Vlad Mihalcea quot                      List lt PostCommentSummary gt  comments   entityManager      createQuery query       unwrap Query class       setResultTransformer Transformers aliasToBean PostCommentSummary class        getResultList     Cool  right

User · Answer

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        lt plugin gt           lt artifactId gt maven-compiler-plugin lt  artifactId gt           lt configuration gt               lt annotationProcessorPaths gt                   lt annotationProcessorPath gt                       lt groupId gt org eclipse persistence lt  groupId gt                       lt artifactId gt org eclipse persistence jpa modelgen processor lt  artifactId gt                       lt version gt 2 7 7 lt  version gt                   lt  annotationProcessorPath gt               lt  annotationProcessorPaths gt               lt compilerArgs gt                   lt arg gt -Aeclipselink persistencexml src main resources META-INF persistence xml lt  arg gt               lt  compilerArgs gt           lt  configuration gt       lt  plugin gt

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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

[java] How to generate the JPA entity Metamodel?

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