Lazy Загрузка в QueryDSL

Question

Я использую структуру DAO с именем «QueryDSL». Когда я запускаю запрос, QueryDSL извлекает все результаты вместе, что не требуется. Я ищу душу, которая позволяет мне загружать результаты в ленивой форме.

Answer 1

В конечном итоге я ввел ленивый список. Это хорошо работает. :)

public class LazyList<T> implements List<T> { 

private SQLQuery query; 
private long size = 0; 
private int limit = 100; 

private Expression<T> exprsn; 
private int offset = 0; 
private List<T> cache = new ArrayList<>(); 

public LazyList(SQLQuery query, Expression<T> exprsn) { 
    this.query = query; 
    this.exprsn = exprsn; 
    size = query.count(); 
    cache = query.limit(limit).offset(offset).list(exprsn); 
} 

@Override 
public int size() { 
    return (int) size; 
} 

@Override 
public boolean isEmpty() { 
    return size == 0; 
} 

@Override 
public T get(int index) { 
    if (index < offset || index > offset + limit) { 
     cache = query.limit(limit).offset(offset).list(exprsn); 
    } 
    return cache.get(index - offset); 
} 

@Override 
public Iterator<T> iterator() { 
    return new Iterator<T>() { 

     private int index = 0; 
     private int offset = 0; 
     private List<T> cache = new ArrayList<>(); 

     { 
      cache = query.limit(limit).offset(offset).list(exprsn); 
     } 

     @Override 
     public boolean hasNext() { 
      return index < size; 
     } 

     @Override 
     public T next() { 
      if (index < offset || index > offset + limit) { 
       cache = query.limit(limit).offset(offset).list(exprsn); 
      } 
      return cache.get(index - offset); 
     } 
    }; 
} 

@Override 
public boolean contains(Object o) { 
    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates. 
} 

@Override 
public Object[] toArray() { 
    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates. 
} 

@Override 
public <T> T[] toArray(T[] a) { 
    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates. 
} 

@Override 
public boolean add(T e) { 
    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates. 
} 

@Override 
public boolean remove(Object o) { 
    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates. 
} 

@Override 
public boolean containsAll(Collection<?> c) { 
    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates. 
} 

@Override 
public boolean addAll(Collection<? extends T> c) { 
    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates. 
} 

@Override 
public boolean addAll(int index, Collection<? extends T> c) { 
    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates. 
} 

@Override 
public boolean removeAll(Collection<?> c) { 
    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates. 
} 

@Override 
public boolean retainAll(Collection<?> c) { 
    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates. 
} 

@Override 
public void clear() { 
    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates. 
} 

@Override 
public T set(int index, T element) { 
    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates. 
} 

@Override 
public void add(int index, T element) { 
    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates. 
} 

@Override 
public T remove(int index) { 
    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates. 
} 

@Override 
public int indexOf(Object o) { 
    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates. 
} 

@Override 
public int lastIndexOf(Object o) { 
    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates. 
} 

@Override 
public ListIterator<T> listIterator() { 
    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates. 
} 

@Override 
public ListIterator<T> listIterator(int index) { 
    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates. 
} 

@Override 
public List<T> subList(int fromIndex, int toIndex) { 
    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates. 
} 

} 

Answer 2

Думаю, вам нужна нумерация страниц.

Прочитать here как его организовать. Вам нужно что-то подобное, чтобы загрузить часть ваших данных.

Page<T> findAll(com.mysema.query.types.Predicate predicate, 
       Pageable pageable) 

Answer 3

Querydsl SQL не поддерживает отложенную загрузку, в Querydsl JPA отложенной загрузки обрабатывается поставщиком JPA.