我的问题是空值必须是最后一个按语句排序。我的代码在下面拍了一下。我使用javax持久标准构建器。我的查询很复杂。
import javax.persistence.criteria.CriteriaBuilder;
public Predicate getSomePredicate() {
Predicate predicate = cb.conjunction();....
...predicate.getExpressions().add(cb.and(cb.or(cb.and(v1, v2), cb.and(s1, s2))));
EOrderByType orderType = EOrderByType.values()[orderBy]
;
switch (orderType) {
case PRICE: cq.where(predicate).orderBy(cb.asc(root.get("price")));
break;
case PRICE_HIGH_TO_LOW: cq.where(predicate).orderBy(cb.desc(root.get("price")));
break;
case CONSUPTION: cq.where(predicate).orderBy(cb.desc(root.get("consume")));
break;
default:
break;
}
return cq.getRestriction();
}
如何使用条件构建器以最后的价格实现订单生成?
答案 0 :(得分:3)
您好我几乎搜索所有互联网页面然后找到解决方案,您可以按部分编写开关案例顺序。如下所示:如果价格为空,则按desc订购,价格值为1000000,如果价格为空则按asc订购,价格值为0.如果你想要这些,你可以写下面的表达式。
EOrderByType orderType = EOrderByType.values()[orderBy];
Expression<Object> queryCase = cb.selectCase().when(cb.isNull(root.get("price")), 100000000).otherwise(root.get("price"));
Direction dir = Direction.ASC;
switch (orderType) {
case UCUZDAN_PAHALIYA:
queryCase = cb.selectCase().when(cb.isNull(root.get("price")), 100000000).otherwise(root.get("price"));
break;
case PAHALIDAN_UCUZA:
queryCase = cb.selectCase().when(cb.isNull(root.get("price")), 0).otherwise(root.get("price"));
dir = Direction.DESC;
break;
}
cq.where(predicate).orderBy(direction( cb, queryCase, dir));
答案 1 :(得分:3)
这是对katsu回答他自己的问题的一个扩展。我试图找到一种解决方案,能够对表的大多数列进行排序,其中某些列可以具有空值。我希望在按升序排序时排序最低非空值前面的空值,并在按降序排序时排序最低非空值之后。换句话说,几乎与(Oracle的)默认行为相反。
我发现其他方法可能会这样做,但是这个方法并不需要我超出Hibernate和JPA 2持久性,但仍然得到我想要的结果。这是从我的实际代码中获取的代码片段,但在一个位置合并并更改了一些名称。您看到的任何语法,编译类型错误都可能是由于这一点。
// sortByColumn is a String containing the Hibernate version of the column name, which had
// been assigned as the ID of the table header column of the column by which we are sorting.
// sortAscending is a Boolean object containing Boolean.TRUE if we are to sort in ascending
// order or Boolean.FALSE or null if we are to sort in descending order. This may seem a
// bit odd, but in the case we need this for, the default sort column is a release date and
// reverse chronological order is the most useful in that case.
// Also defined are: CriteriaQuery<SoftwareVersion> criteriaQuery and
// CriteriaBuilder criteriaBuilder by the typical means.
final Root<SoftwareVersion> softwareVersionRoot =
criteriaQuery.from(SoftwareVersion.class);
private static final String EMPTY_STRING = "";
if (sortByColumn != null && sortByColumn.trim().length() > 0) {
Order sortOrder;
Expression<String> sortColumnExpression;
if (sortByColumn.equalsIgnoreCase(SoftwareVersion_.installationFileLength.getName()) ||
sortByColumn.equalsIgnoreCase(SoftwareVersion_.releaseTimestamp.getName())) {
// The two non-String fields (exposed to the user) that we don't need to have the
// lower() function operate upon.
sortColumnExpression = oemSoftwareVersionRoot.get(sortByColumn);
} else {
// We use the lower() function to enforce case insensitive sorting on the columns we
// show to the user, which are all Strings except as noted above.
Expression<String> rootExpression = oemSoftwareVersionRoot.get(sortByColumn);
sortColumnExpression = criteriaBuilder.lower(rootExpression);
}
// The columns for installation file name, installation file length and release timestamp
// are just three of the columns that we allow the user to sort by. However, these three
// may have null values in the database, and require some special handling.
if (sortByColumn.equalsIgnoreCase(SoftwareVersion_.installationFileLength.getName()) ||
sortByColumn.equalsIgnoreCase(SoftwareVersion_.installationFileName.getName()) ||
sortByColumn.equalsIgnoreCase(SoftwareVersion_.releaseTimestamp.getName())
) {
Expression<Object> queryCase;
if (sortByColumn.equalsIgnoreCase(SoftwareVersion_.installationFileName.getName())) {
// Installation file name is a (case insensitive) String
queryCase = criteriaBuilder.selectCase().when(
criteriaBuilder.isNull(sortColumnExpression),
StringUtil.EMPTY_STRING).otherwise(sortColumnExpression);
} else if (sortByColumn.equalsIgnoreCase(SoftwareVersion_.releaseTimestamp.getName())) {
// Release timestamp is a database timestamp
LocalDateTime dateTime = LocalDateTime.of(1970,1,1,0,0);
// Equivalent to Unix epoch time. Note month is 1-12, not 0-11
queryCase = criteriaBuilder.selectCase().when(
criteriaBuilder.isNull(sortColumnExpression),
Timestamp.valueOf(dateTime)).otherwise(sortColumnExpression);
} else {
// Installation file length is a Long (or BigDecimal) computed when the file is uploaded.
// The user can't set or change it, but can sort by it.
queryCase = criteriaBuilder.selectCase().when(
criteriaBuilder.isNull(sortColumnExpression),
Long.valueOf(0)).otherwise(sortColumnExpression);
}
if (asc != null && asc.booleanValue()) {
sortOrder = criteriaBuilder.asc(queryCase);
} else {
sortOrder = criteriaBuilder.desc(queryCase);
}
} else {
if (asc != null && asc.booleanValue()) {
sortOrder = criteriaBuilder.asc(sortColumnExpression);
} else {
sortOrder = criteriaBuilder.desc(sortColumnExpression);
}
}
criteriaQuery.orderBy(sortOrder);
}