如何使用JPA条件查询api来连接列？
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我是JPA的新手，对此有疑问。
假设我们有两个相关的表
由ManytoOne协会提供，这意味着
表A在其中存储表B的主键。
当这两个表映射到JPA实体时
我在这种情况下需要搜索。
我已经使用了richfaces演示中的现有代码，通过使用来处理过滤和排序
JPA。此代码使用输入参数来创建条件查询。
这是代码：
private CriteriaQuery<T> createSelectCriteriaQuery() {
CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
CriteriaQuery<T> criteriaQuery = criteriaBuilder.createQuery(entityClass);
Root<T> root = criteriaQuery.from(entityClass);
if (arrangeableState != null) {
List<Order> orders = createOrders(criteriaBuilder, root);
if (!orders.isEmpty()) {
criteriaQuery.orderBy(orders);
}
Expression<Boolean> filterCriteria = createFilterCriteria(criteriaBuilder, root);
if (filterCriteria != null) {
criteriaQuery.where(filterCriteria);
}
}
return criteriaQuery;
}
protected Expression<Boolean> createFilterCriteriaForField(String propertyName, Object filterValue, Root<T> root, CriteriaBuilder criteriaBuilder) {
String stringFilterValue = (String) filterValue;
if (Strings.isNullOrEmpty(stringFilterValue)) {
return null;
}
stringFilterValue = stringFilterValue.toLowerCase(arrangeableState.getLocale());
Path<String> expression = root.get(propertyName);
Expression<Integer> locator = criteriaBuilder.locate(criteriaBuilder.lower(expression), stringFilterValue, 1);
return criteriaBuilder.gt(locator, 0);
}
private Expression<Boolean> createFilterCriteria(CriteriaBuilder criteriaBuilder, Root<T> root) {
Expression<Boolean> filterCriteria = null;
List<FilterField> filterFields = arrangeableState.getFilterFields();
if (filterFields != null && !filterFields.isEmpty()) {
FacesContext facesContext = FacesContext.getCurrentInstance();
for (FilterField filterField : filterFields) {
String propertyName = (String) filterField.getFilterExpression().getValue(facesContext.getELContext());
Object filterValue = filterField.getFilterValue();
Expression<Boolean> predicate = createFilterCriteriaForField(propertyName, filterValue, root, criteriaBuilder);
if (predicate == null) {
continue;
}
if (filterCriteria == null) {
filterCriteria = predicate.as(Boolean.class);
} else {
filterCriteria = criteriaBuilder.and(filterCriteria, predicate.as(Boolean.class));
}
}
}
return filterCriteria;
}
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