在开发中,用到动态查询的地方,所有的查询条件包括分页参数,都会被封装成一个查询类XxxQuery
比如说上一篇中的Item
那么ItemQuery就像这样
@Data
public class ItemQuery {
private Integer itemId;//id精确查询 =
private String itemName;//name模糊查询 like
//价格查询
private Integer itemPrice;// 价格小于'条件' <
}
那现在问题来了,如何去标识这些字段该用怎样的查询条件连接呢,还要考虑到每个查询类都可以通用.
可以用字段注解,来标识字段的查询连接条件
//用枚举类表示查询连接条件
public enum MatchType {
equal, // filed = value
//下面四个用于Number类型的比较
gt, // filed > value
ge, // field >= value
lt, // field < value
le, // field <= value
notEqual, // field != value
like, // field like value
notLike, // field not like value
// 下面四个用于可比较类型(Comparable)的比较
greaterThan, // field > value
greaterThanOrEqualTo, // field >= value
lessThan, // field < value
lessThanOrEqualTo, // field <= value
;
}
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface QueryWord {
// 数据库中字段名,默认为空字符串,则Query类中的字段要与数据库中字段一致
String column() default "";
// equal, like, gt, lt...
MatchType func() default MatchType.equal;
// object是否可以为null
boolean nullable() default false;
// 字符串是否可为空
boolean emptiable() default false;
}
好了,现在我们可以改造一下ItemQuery了
@Data
public class ItemQuery {
@QueryWord(column = "item_id", func = MatchType.equal)
private Integer itemId;
@QueryWord(func = MatchType.like)
private String itemName;
@QueryWord(func = MatchType.le)
private Integer itemPrice;
}
现在,我们还需要去构造出查询时的动态条件,那就创建一个所有查询类的基类BaseQuery,我们把分页的条件字段放在基类里.
/**
* 所有查询类的基类
*/
@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
public abstract class BaseQuery<T> {
// start from 0
protected int pageIndex = 0;
protected int pageSize = 10;
/**
* 将查询转换成Specification
* @return
*/
public abstract Specification<T> toSpec();
//JPA分页查询类
public Pageable toPageable() {
return new PageRequest(pageIndex, pageSize);
}
//JPA分页查询类,带排序条件
public Pageable toPageable(Sort sort) {
return new PageRequest(pageIndex, pageSize, sort);
}
//动态查询and连接
protected Specification<T> toSpecWithAnd() {
return this.toSpecWithLogicType("and");
}
//动态查询or连接
protected Specification<T> toSpecWithOr() {
return this.toSpecWithLogicType("or");
}
//logicType or/and
private Specification<T> toSpecWithLogicType(String logicType) {
BaseQuery outerThis = this;
return (root, criteriaQuery, cb) -> {
Class clazz = outerThis.getClass();
//获取查询类Query的所有字段,包括父类字段
List<Field> fields = getAllFieldsWithRoot(clazz);
List<Predicate> predicates = new ArrayList<>(fields.size());
for (Field field : fields) {
//获取字段上的@QueryWord注解
QueryWord qw = field.getAnnotation(QueryWord.class);
if (qw == null)
continue;
// 获取字段名
String column = qw.column();
//如果主注解上colume为默认值"",则以field为准
if (column.equals(""))
column = field.getName();
field.setAccessible(true);
try {
// nullable
Object value = field.get(outerThis);
//如果值为null,注解未标注nullable,跳过
if (value == null && !qw.nullable())
continue;
// can be empty
if (value != null && String.class.isAssignableFrom(value.getClass())) {
String s = (String) value;
//如果值为"",且注解未标注emptyable,跳过
if (s.equals("") && !qw.emptiable())
continue;
}
//通过注解上func属性,构建路径表达式
Path path = root.get(column);
switch (qw.func()) {
case equal:
predicates.add(cb.equal(path, value));
break;
case like:
predicates.add(cb.like(path, "%" + value + "%"));
break;
case gt:
predicates.add(cb.gt(path, (Number) value));
break;
case lt:
predicates.add(cb.lt(path, (Number) value));
break;
case ge:
predicates.add(cb.ge(path, (Number) value));
break;
case le:
predicates.add(cb.le(path, (Number) value));
break;
case notEqual:
predicates.add(cb.notEqual(path, value));
break;
case notLike:
predicates.add(cb.notLike(path, "%" + value + "%"));
break;
case greaterThan:
predicates.add(cb.greaterThan(path, (Comparable) value));
break;
case greaterThanOrEqualTo:
predicates.add(cb.greaterThanOrEqualTo(path, (Comparable) value));
break;
case lessThan:
predicates.add(cb.lessThan(path, (Comparable) value));
break;
case lessThanOrEqualTo:
predicates.add(cb.lessThanOrEqualTo(path, (Comparable) value));
break;
}
} catch (Exception e) {
continue;
}
}
Predicate p = null;
if (logicType == null || logicType.equals("") || logicType.equals("and")) {
p = cb.and(predicates.toArray(new Predicate[predicates.size()]));//and连接
} else if (logicType.equals("or")) {
p = cb.or(predicates.toArray(new Predicate[predicates.size()]));//or连接
}
return p;
};
}
//获取类clazz的所有Field，包括其父类的Field
private List<Field> getAllFieldsWithRoot(Class<?> clazz) {
List<Field> fieldList = new ArrayList<>();
Field[] dFields = clazz.getDeclaredFields();//获取本类所有字段
if (null != dFields && dFields.length > 0)
fieldList.addAll(Arrays.asList(dFields));
// 若父类是Object，则直接返回当前Field列表
Class<?> superClass = clazz.getSuperclass();
if (superClass == Object.class) return Arrays.asList(dFields);
// 递归查询父类的field列表
List<Field> superFields = getAllFieldsWithRoot(superClass);
if (null != superFields && !superFields.isEmpty()) {
superFields.stream().
filter(field -> !fieldList.contains(field)).//不重复字段
forEach(field -> fieldList.add(field));
}
return fieldList;
}
}
在BaseQuery里,就通过toSpecWithAnd() toSpecWithOr()方法动态构建出了查询条件.
那现在ItemQuery就要继承BaseQuery,并实现toSpec()抽象方法
@Data
public class ItemQuery extends BaseQuery<Item> {
@QueryWord(column = "item_id", func = MatchType.equal)
private Integer itemId;
@QueryWord(func = MatchType.like)
private String itemName;
@QueryWord(func = MatchType.le)
private Integer itemPrice;
@Override
public Specification<Item> toSpec() {
return super.toSpecWithAnd();//所有条件用and连接
}
}
当然肯定还有其他不能在BaseQuery中构建的查询条件,那就在子类的toSpec()实现中添加,
比如下面的例子,ItemQuery条件改成这样
@QueryWord(column = "item_id", func = MatchType.equal)
private Integer itemId;
@QueryWord(func = MatchType.like)
private String itemName;
//价格范围查询
private Integer itemPriceMin;
private Integer itemPriceMax;
那其他条件就可以在toSpec()添加,这样就可以很灵活的构建查询条件了
@Override
public Specification<Item> toSpec() {
Specification<Item> spec = super.toSpecWithAnd();
return ((root, criteriaQuery, criteriaBuilder) -> {
List<Predicate> predicatesList = new ArrayList<>();
predicatesList.add(spec.toPredicate(root, criteriaQuery, criteriaBuilder));
if (itemPriceMin != null) {
predicatesList.add(
criteriaBuilder.and(
criteriaBuilder.ge(
root.get(Item_.itemPrice), itemPriceMin)));
}
if (itemPriceMax != null) {
predicatesList.add(
criteriaBuilder.and(
criteriaBuilder.le(
root.get(Item_.itemPrice), itemPriceMax)));
}
return criteriaBuilder.and(predicatesList.toArray(new Predicate[predicatesList.size()]));
});
}
调用:
@Test
public void test1() throws Exception {
ItemQuery itemQuery = new ItemQuery();
itemQuery.setItemName("车");
itemQuery.setItemPriceMax(50);
itemQuery.setItemPriceMax(200);
Pageable pageable = itemQuery.toPageable(new Sort(Sort.Direction.ASC, "itemId"));
Page<Item> all = itemRepository.findAll(itemQuery.toSpec(), pageable);
}
现在这个BaseQuery和QuertWord就可以在各个动态查询处使用了,只需在查询字段上标注@QueryWord注解,
然后实现BaseQuery中的抽象方法toSpec(),通过JpaSpecificationExecutor接口中的这几个方法,就可以实现动态查询了,是不是很方便.
public interface JpaSpecificationExecutor<T> {
T findOne(Specification<T> var1);
List<T> findAll(Specification<T> var1);
Page<T> findAll(Specification<T> var1, Pageable var2);
List<T> findAll(Specification<T> var1, Sort var2);
long count(Specification<T> var1);
}
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