Question

我使用JPA条件API从日期库中获取记录。我有实体记录，字段 dateTime ，可以为null。我会编码：

public List<Record> find(RecordFilter recordFilter, int page, int pageSize) {
    CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
    CriteriaQuery<Record> criteriaQuery = criteriaBuilder.createQuery(Record.class);
    Root<Record> recordRoot = criteriaQuery.from(Record.class);

    /*
     * JOINS. Left Joins are used for optional fields, or fields inside of the optional fields.
     */
    Join<Record, Agency> recordAgencyJoin = recordRoot.join(RecordTable.FIELD_AGENCY);
    //Some other joins

    //This is where I had the problem. 
    applyOrderBy(criteriaQuery, criteriaBuilder, recordRoot);

    /*
     * Specify which columns to select and their order.
     * criteriaQuery.multiselect(....);
     */              
    applyMultiSelect(recordRoot, recordAgencyJoin, /*other joins*/ criteriaQuery);

    /*
     * criteriaQuery.where(somePredicate);
     */
    applyFilter(recordFilter, criteriaQuery, criteriaBuilder,
            recordRoot, recordAgencyJoin /*, other joins*/);
    TypedQuery<Record> query = entityManager.<Record>createQuery(criteriaQuery);
    RepositoryUtils.applyPagination(query, page, pageSize);
    return query.getResultList();
}


private void applyOrderBy(CriteriaBuilder criteriaBuilder, Root<Record> recordRoot, CriteriaQuery<Record> criteriaQuery) {
    //Other fields to be added to the final sort.

    Order dateTimeDescOrder = criteriaBuilder.desc(recordRoot.get(RecordTable.FIELD_DATE_TIME));
    criteriaQuery.orderBy(dateTimeDescOrder /*, other orders by*/);
}

事实证明，首先显示带有NULL dateTimeField的记录。我使用Postrgres数据库。我会回答这个问题，因为我找到了解决方案。这是一篇类似的帖子。 JPA Criteria Query API and order by null last

Answer 1

我在这里回答了这个任务。

首先，Postgres默认首先返回空值。

SELECT * FROM record ORDER BY date_time_field DESC;

https://stackoverflow.com/a/7621232/4587961

SELECT * FROM record ORDER BY date_time_field DESC NULLS LAST;

其次，我必须更改 applyOrderBy 方法

private void applyOrderBy(CriteriaBuilder criteriaBuilder, Root<Record> recordRoot, CriteriaQuery<Record> criteriaQuery) {
    //In the class code
    //private static final Date MIN_DATE = new Date(0L);
    final Date MIN_DATE = new Date(0L);

    //We treat records will NULL dateTimeField as if it was MIN_DATE.
    Order dateTimeDescOrder = criteriaBuilder.desc(
            //NULL values - last - WORKAROUND.
            criteriaBuilder.coalesce(recordRoot.get(RecordTable.FIELD_DATE_TIME), MIN_DATE));
    criteriaQuery.orderBy(dateTimeDescOrder);
}

注意，来自hibernate-jpa-2.1的 CriteriaBuilder 。

/**
 * Create an expression that returns null if all its arguments
 * evaluate to null, and the value of the first non-null argument
 * otherwise.
 *
 * @param x expression
 * @param y value
 *
 * @return coalesce expression
 */
<Y> Expression<Y> coalesce(Expression<? extends Y> x, Y y);

Answer 2

JPA规范中没有任何内容可以控制NULLS的处理方式（并且所有RDBMS都优先使用默认值）。这在JPQL（基于字符串的查询）或Criteria API中都不可用。使用JPQL，所有主要的JPA提供程序都允许使用

NULLS [FIRST|LAST]

在订购条款中。对于Criteria，您受到Criteria API的约束，因此无法做到。我知道DataNucleus JPA提供了JPA Criteria API的自定义版本，允许指定

Order order = criteriaBuilder.asc(myExpression).nullsFirst();

但很明显，这是特定于该JPA提供者。

Answer 3

在JPA或Eclipselink中没有任何东西可以在CriteriaBuilder中使用案例。

示例：

Order order1 = cBuilder.desc(cBuilder.selectCase().when(cBuilder.isNotNull(from.get('ColumnName1')), from.get('ColumnName1')).otherwise(from.get('ColumnName1')));
CQuery.orderBy(order1);

它将为您提供最佳答案

Answer 4

我将JPA与eclipselink和Postgres一起使用，并且这里的namedquery可以正常工作。这是摘录：

,@NamedQuery(name = "ServerPasswords.forTheServer",
            query = "SELECT ss FROM ServerPasswords ss WHERE ss.fkIds = :IDServer AND ss.private = FALSE "
            + "ORDER BY ss.servce, ss.active DESC, ss.datefrom DESC NULLS LAST, ss.dateto NULLS LAST")

JPA条件API最后按NULL顺序排序

4 个答案: