问题
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.
回答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).
来源：https://stackoverflow.com/questions/9025196/how-to-use-jpa-criteria-api-when-joining-many-tables