quarkus-panache-smells

Quarkus Panache Repository Code Smells Detection

Identify and fix common ORM anti-patterns in Quarkus Panache applications using the Repository pattern.

Code Smell Categories

1. Eager Fetching at Class Level

Problem: FetchType.EAGER on relationships always loads related entities.

Detection:

// BAD: Always loads Person even when not needed
@ManyToOne(fetch = FetchType.EAGER)
public Person owner;

// BAD: @ManyToOne/@OneToOne default to EAGER
@ManyToOne  // implicitly EAGER
public Person owner;

Refactoring:

// GOOD: Explicitly LAZY
@ManyToOne(fetch = FetchType.LAZY)
public Person owner;

---

2. Using listAll() Without Pagination

Problem: listAll() or streamAll() on large tables causes memory issues.

Detection:

// BAD: Loads entire table into memory
List<Person> all = personRepository.listAll();

// BAD: Even with stream, still fetches all
Stream<Person> stream = personRepository.streamAll();

Refactoring:

// GOOD: Use PanacheQuery with pagination
PanacheQuery<Person> query = personRepository.findAll();
query.page(Page.ofSize(25));
List<Person> page = query.list();

// Or with range
List<Person> range = personRepository.findAll().range(0, 24).list();

---

3. Missing Projections for Read-Only Queries

Problem: Fetching entire entities when only specific fields are needed.

Detection:

// BAD: Loads all columns including BLOBs
List<Person> persons = personRepository.list("status", Status.Alive);
// Then only uses person.name

Refactoring:

// GOOD: Use DTO projection
@RegisterForReflection
public class PersonName {
    public final String name;
    public PersonName(String name) {
        this.name = name;
    }
}

// Only 'name' column loaded from database
List<PersonName> names = personRepository.find("status", Status.Alive)
    .project(PersonName.class)
    .list();

With related entity fields:

@RegisterForReflection
public class DogDto {
    public String name;
    public String ownerName;

    public DogDto(String name,
                  @ProjectedFieldName("owner.name") String ownerName) {
        this.name = name;
        this.ownerName = ownerName;
    }
}

List<DogDto> dogs = dogRepository.findAll().project(DogDto.class).list();

---

4. N+1 Problem: Lazy Access in Loop

Problem: Accessing LAZY relationships inside loops triggers N queries.

Detection:

// BAD: Each iteration triggers a query
List<Person> persons = personRepository.listAll();
for (Person p : persons) {
    p.address.city;  // N+1 queries!
}

Refactoring:

// Option 1: Use @BatchSize on relationship
@OneToMany(fetch = FetchType.LAZY)
@BatchSize(size = 25)
public List<Order> orders;

// Option 2: JOIN FETCH in query through Repository
List<Person> persons = personRepository.find(
    "FROM Person p LEFT JOIN FETCH p.address"
).list();

// Option 3: Use EntityGraph in Repository method
public List<Person> findAllWithAddress() {
    return find("FROM Person p").withHint("javax.persistence.fetchgraph", "person-with-address").list();
}

---

5. N+1 Problem: Missing JOIN FETCH for Eager Relations

Problem: Queries on entities with EAGER relationships generate N additional queries.

Detection:

// Entity has @ManyToOne(fetch = FetchType.EAGER)
// Query doesn't use JOIN FETCH
List<Dog> dogs = dogRepository.list("breed", "Labrador");  // N+1!

Refactoring:

// GOOD: Explicit JOIN FETCH
List<Dog> dogs = dogRepository.find(
    "FROM Dog d JOIN FETCH d.owner WHERE d.breed = ?1",
    "Labrador"
).list();

---

6. Unidirectional @OneToMany with List

Problem: Adding/removing elements causes DELETE ALL + N INSERTs.

Detection:

// BAD: Unidirectional with List
@Entity
public class Person { // Standard Entity (no PanacheEntity)
    @Id @GeneratedValue public Long id;

    @OneToMany(cascade = CascadeType.ALL)
    public List<Order> orders = new ArrayList<>();
}

Refactoring:

// Option 1: Make bidirectional
@Entity
public class Person {
    @Id @GeneratedValue public Long id;

    @OneToMany(mappedBy = "person", cascade = CascadeType.ALL)
    public List<Order> orders = new ArrayList<>();
}

@Entity
public class Order {
    @Id @GeneratedValue public Long id;

    @ManyToOne(fetch = FetchType.LAZY)
    public Person person;
}

// Option 2: Use Set (single INSERT per operation)
@OneToMany(cascade = CascadeType.ALL)
public Set<Order> orders = new HashSet<>();

---

7. Not Closing Streams

Problem: Unclosed streams hold database connections.

Detection:

// BAD: Stream not closed, leaks connection
Stream<Person> persons = personRepository.streamAll();
persons.map(p -> p.name).collect(toList());

Refactoring:

// GOOD: Use try-with-resources
try (Stream<Person> persons = personRepository.streamAll()) {
    return persons.map(p -> p.name).collect(toList());
}

---

8. Ignoring Panache Query Methods

Problem: Writing verbose HQL when Panache shortcuts exist.

Detection:

// BAD: Verbose HQL for simple queries
personRepository.find("SELECT p FROM Person p WHERE p.status = ?1", Status.Alive);

Refactoring:

// GOOD: Panache simplified query
personRepository.find("status", Status.Alive);

// GOOD: Multiple parameters
personRepository.find("status = ?1 and name = ?2", Status.Alive, "John");

// GOOD: Named parameters
personRepository.find("status = :status",
    Parameters.with("status", Status.Alive));

Quick Reference Table

Smell	Detection	Fix
Eager class-level	FetchType.EAGER or missing LAZY on @*ToOne	Add FetchType.LAZY
No pagination	listAll() / streamAll() on large tables	Use repo.findAll().page()
No projection	Full entity for read-only	Use .project(Dto.class)
N+1 in loop	LAZY access in for loop	@BatchSize or JOIN FETCH
N+1 Eager	Query without FETCH for EAGER relations	Add JOIN FETCH in repo
Unidirectional List	@OneToMany without mappedBy + List	Use Set or bidirectional
Unclosed stream	stream() without try-with-resources	Wrap in try()
Verbose HQL	Full SELECT for simple queries	Use Panache shortcuts
Missing reflection	DTO without @RegisterForReflection	Add annotation

Panache-Specific Best Practices

1. Use Repository Pattern (PanacheRepository) to separate data access logic from the entity model.
2. Use @ApplicationScoped for your repositories.
3. Use find() over list() when you need pagination/projection.
4. Configure fetch batch size globally: quarkus.hibernate-orm.fetch.batch-size=25
5. Use @Transactional on write operations in your service or repository layer.