Now we can implement Querydsl-queries in the FruitFragmentImpl. The class requires a JPA EntityManager to interact with the persistent entities, which is passed to the JPAQuery constructor when instantiating a query.
In order to define the Fruit-entity as the source of the query, we need to create its Q-type first by accessing its static fruit field. Then, we can call query.from(fruit).
To retrieve a fruit with a given name, we can use a where-clause with the eq (equals) operator to get fruits with the name equal to the one passed to the function parameter. Additionally, we can sort the results by name in descending alphabetical order by calling query.orderBy(fruit.name.desc()) before fetching the result.
public class FruitFragmentImpl implements FruitFragment {
@Inject EntityManager em;
@Override
public List<Fruit> findAllQueryDslName(String name) {
JPAQuery<Fruit> query = new JPAQuery<Fruit>(this.em);
QFruit fruit = QFruit.fruit;
query.from(fruit);
if (name != null && !name.isEmpty()) {
query.where(fruit.name.eq(name));
}
return query.orderBy(fruit.name.desc()).fetch();
}
We can also get fruits in a given price range by calling fruit.price.between(min, max) in the where-clause. To see usage of further comparators, see the findAllQueryDslMaxPriceDesc`and `findAllQueryDslMinPriceAsc functions.
@Override
public List<Fruit> findAllQueryDslPriceRange(Float min, Float max) {
...
if (min != null && min != 0 && max != null && max != 0) {
query.where(fruit.price.between(min, max));
}
return query.orderBy(fruit.price.desc()).fetch();
}