How to use JPA Criteria API when joining many tables

Question

This is the further question to this:

How to use JPA Criteria API in JOIN

CriteriaBuilder criteriaBuilder = em.getCriteriaBuilder();

CriteriaQuery<Company> criteria = criteriaBuilder.createQuery( Company.class );
Root<Company> companyRoot = criteria.from( Company.class );
Join<Company,Product> products = companyRoot.join("dentist");
Join<Company, City> cityJoin = companyRoot.join("address.city");//Company->Address->City-city
criteria.where(criteriaBuilder.equal(products.get("category"), "dentist"),      criteriaBuilder.equal(cityJoin.get("city"),"Leeds"));

A company has an address, inside the address there is City-pojo and Country-Pojo. How can I use it in JOIN? I tried to reference it with address.city but I got the error message:

The attribute [address.city] from the managed type [EntityTypeImpl@1692700229:Company [ javaType: class com.test.domain.Company descriptor: RelationalDescriptor(com.test.domain.Company --> [DatabaseTable(COMPANY)]), mappings: 16]] is not present.

Answer 1

If you use canonical Metamodel, you'll avoid this kind of errors. In your code you have misused the "dentist" keyword, that's probably the cause of your error, because "dentist" is not a field in Company entity.

However, looking at how you defined your class in the other question, the way to define that join using Metamodel is this:

SetJoin<Company,Product> products = companyRoot.join(Company_.products); 

As you can see, Metamodel avoids the use of strings, and so avoids a lot of runtime errors. If anyway you don't use Metamodel, try this:

SetJoin<Company,Product> products = companyRoot.join("products"); 

If you now want to add a predicate, i.e. something after the where, you'll write something like:

Predicate predicate = criteriaBuilder.equal(products.get(Product_.category), "dentist");
criteria.where(predicate);

If you want to add a join for the City entity:

Join<Company, City> city = companyRoot.join(Company_.city);
predicate = criteriaBuilder.and(predicate, criteriaBuilder.equal(city.get(City_.cityName), "Leeds");
criteria.where(predicate);

(supposing that the field cityName is the correct field name for your city).

Answer 2

Agree with @perissf.

I can't comment but the symbol "Company_" is the metadata class file which contains all the attribute name of the model class.

I strongly suggest to use metadata classes, you can autogenerate metadata classes using the maven processor plugin using org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor as processor in your configuration.

This example pom plugin xml should work it out :

  <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.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>