双语网站建设方案软文营销是什么意思
文章目录
- And Or
- 迷惑
- 原因
- 告别InvalidMongoDbApiUsageException
- 问题
- 简单解决
- 根本解决
- 修改源码
- 代码(省流,可以直接看这里)
And Or
很多时候都需要进行逻辑的与或操作,但是spring当中自带的操作并不好用,于是做了相关的改进,首先来看原本的操作:
// or操作
Criteria criteriaA = new Criteria();
criteriaA.orOperator(Criteria.where("name").is("wang"),Criteria.where("age").is("18")
);// and操作 ,这里为了图省事,直接用了一样的条件,只有方法不同
Criteria criteriaB = new Criteria();
criteriaB.andOperator( // 这里跟上面不一样,用的是andOperatorCriteria.where("name").is("wang"),Criteria.where("age").is("18")
);
迷惑
这里存在一个问题,就是当我们试图将这两个Criteria合并起来查询的时候,就会报错:
Query query = new Query();
query.addCriteria(criteriaA);
query.addCriteria(criteriaB);
System.out.println(query);/* 报错如下
org.springframework.data.mongodb.InvalidMongoDbApiUsageException: Due to limitations of the com.mongodb.BasicDocument, you can't add a second 'null' criteria. Query already contains '{ "$or" : [{ "name" : "wang"}, { "age" : "18"}]}'
*/
这就非常迷惑了,报错内容是我们不能添加两个键值为null的criteria,可是我们添加的明明是$or和$and。要解释这个问题要深入解析一下Criteria的构成。
原因
Criteria其中有四个属性
private String key;
private List<Criteria> criteriaChain;
private LinkedHashMap<String, Object> criteria = new LinkedHashMap();
private Object isValue;
- key 表示键值
- criteriaChain 是一个链表,存储了其他筛选的条件,当执行criteria.and().is()操作的时候,就会添加在其中
- criteria 是一个Map,存储了除了is以外的筛选条件,例如gt/ne之类的
- isValue 存放了criteria.is()方法设置的值
这里,如果我们采用无参构造方法new Criteria()
public Criteria() {this.isValue = NOT_SET;this.criteriaChain = new ArrayList();
}
就会造成key值为空null,当我们将两个Criteria合并起来查询的时候,就会报错了。
解决方法
最简单的解决方法,就是只使用一次new Criteria()方法:
Criteria criteriaA = new Criteria();
criteriaA.orOperator(Criteria.where("name").is("wang"),Criteria.where("age").is("18")
);
criteriaA.andOperator(Criteria.where("name").is("wang"),Criteria.where("age").is("18")
);
Query query = new Query();
query.addCriteria(criteriaA);
System.out.println(query);
如果是逻辑不复杂的话,那么这样就OK了。但是,这里仍然埋了一个雷,那就是criteriaA的键值仍然为空,很有可能在其他地方报错。让我们冷静分析一下,这里问题的根源是没有一个静态方法可以直接创造一个and/or类型的Criteria对象,OK,下面来继续深入探索一下为什么没有静态方法呢。
我们点开orOperator方法,看看他怎么实现的
public Criteria orOperator(Collection<Criteria> criteria) {Assert.notNull(criteria, "Criteria must not be null!");BasicDBList bsonList = this.createCriteriaList(criteria);return this.registerCriteriaChainElement((new Criteria("$or")).is(bsonList));
}
我们会发现一个大无语事件,这东西就是单纯地将"$or"作为键值重新构造了一个Criteria对象,然后续到了原有criteriaChain的后面,所以从技术上来说完全没有问题啊?开发者就是懒得没写$or/$and的静态方法,那我们自己来写好了:
public class CriteriaUtil{public static Criteria and(Criteria... criteria){return and(Arrays.asList(criteria));}public static Criteria and(Collection<Criteria> criteria) {BasicDBList bsonList = createCriteriaList(criteria);return new Criteria("$and").is(bsonList);}public static Criteria or(Criteria... criteria){return or(Arrays.asList(criteria));}public static Criteria or(Collection<Criteria> criteria){BasicDBList bsonList = createCriteriaList(criteria);return new Criteria("$or").is(bsonList);}private static BasicDBList createCriteriaList(Collection<Criteria> criteria) {BasicDBList bsonList = new BasicDBList();for (Criteria c : criteria) {bsonList.add(c.getCriteriaObject());}return bsonList;}
}
顺便一提,上面的createCriteriaList是从源码里面抄过来的,以及源码这个方法没有写成静态的,还写成私有的了
Criteria criteriaA = CriteriaUtil.or(Criteria.where("name").is("wang"),Criteria.where("age").is("18")
);
Criteria criteriaB = CriteriaUtil.and(Criteria.where("name").is("wang"),Criteria.where("age").is("18")
);
Query query = new Query();
query.addCriteria(criteriaA);
query.addCriteria(criteriaB);
System.out.println(query);
至此,问题得以优雅地解决。多说一句为什么要采用这么复杂的解决方法呢,因为我的项目当中有很多criteriaA/B/C/D,并且中间代码跨度很大,修改Criteria本身反倒简单。
下面通过反射机制来重写Criteria。
告别InvalidMongoDbApiUsageException
问题
在绝大部分情况下,如果我们对同一个字段设置了不同的条件,我们都是希望这些条件同时要满足,比如一下例子:
Criteria criteria = Criteria.where("A").gt(100);
criteria.and("B").is("b");
... ...criteria.and("A").lt(200);
首先我们设置了“A>100”的条件,经过一些判断之后,我们又需要添加“A<200”的条件,但这样是会运行报错的
InvalidMongoDbApiUsageException: Due to limitations of the org.bson.Document, you can’t add a second ‘A’ expression specified as ‘A : Document{{KaTeX parse error: Expected 'EOF', got '}' at position 7: lt=200}̲}'. Criteria al…gt=100}}’.
简单解决
最简单的解决办法就是合并两个条件,在代码当中写到一起:
Criteria criteria = Criteria.where("A").gt(100).lt(200);
criteria.and("B").is("b");
System.out.println(Query.query(criteria));
结果如下:
Query: { "A" : { "$gt" : 100, "$lt" : 200}, "B" : "b"}, Fields: {}, Sort: {}
但这样调整了我们条件的顺序,要求我们必须将对同一字段的筛选条件写在一起,不能分开。这是因为在Spring框架当中使用MongoDB时,对于某个字段的条件筛选只能设置一次,设置完成之后才能设置其他字段的条件。并且,这种情况对于$and/$or也是一样的:
比如两个$or:
Criteria criteria = new Criteria();
criteria.orOperator(Criteria.where("A").is("a"),Criteria.where("B").is("b")
);
criteria.orOperator(Criteria.where("C").is("c"),Criteria.where("D").is("d")
);
System.out.println(Query.query(criteria));
对于这种问题的简单解决办法是用and将两个or操作包起来:
Criteria criteriaA = new Criteria();
criteriaA.orOperator(Criteria.where("A").is("a"),Criteria.where("B").is("b")
);Criteria criteriaB = new Criteria();
criteriaB.orOperator(Criteria.where("C").is("c"),Criteria.where("D").is("d")
);
Criteria criteria = new Criteria();
criteria.andOperator(criteriaA,criteriaB);
System.out.println(Query.query(criteria));
根本解决
简单的解决办法其实就是把不同的条件写到一起,或者用and包起来。但实际情况当中,我们很可能需要在已经生成的Criteria上面继续添加条件,这时如果之前对某个字段设置过条件,就无法再次添加条件了,或者将二者用很多$and包起来。为了优雅的处理这种情况,我们需要深入源码来探究一下。
Criteria对象是通过getCriteriaObject方法转化为Document的,来生成MongoDB当中可执行的语句:
public Document getCriteriaObject() {if (this.criteriaChain.size() == 1) {return ((Criteria)this.criteriaChain.get(0)).getSingleCriteriaObject();} else if (CollectionUtils.isEmpty(this.criteriaChain) && !CollectionUtils.isEmpty(this.criteria)) {return this.getSingleCriteriaObject();} else {Document criteriaObject = new Document();Iterator var2 = this.criteriaChain.iterator();while(var2.hasNext()) {Criteria c = (Criteria)var2.next();Document document = c.getSingleCriteriaObject();Iterator var5 = document.keySet().iterator();while(var5.hasNext()) {String k = (String)var5.next();this.setValue(criteriaObject, k, document.get(k));}}return criteriaObject;}
}
上面这个函数不用细看,其中的setValue方法是抛出异常的关键:
private void setValue(Document document, String key, Object value) {Object existing = document.get(key);if (existing == null) {document.put(key, value);} else {throw new InvalidMongoDbApiUsageException("Due to limitations of the org.bson.Document, you can't add a second '" + key + "' expression specified as '" + key + " : " + value + "'. Criteria already contains '" + key + " : " + existing + "'.");}
}
逻辑非常简单了,首先判断Document当中有没有key值,没有的话就插入<key,value>,有的话就报错。那么解决的方法也就有了,如果往Document中插入时起了冲突,那么就用$and将二者进行合并。
修改源码
修改完成的setValue函数如下:
private static void setValue(Document document, String key, Object value) {Object existing = document.get(key);if (existing == null) {document.put(key, value);} else {if(key.equals("$and")){if(value.getClass() != BasicDBList.class || existing.getClass() != BasicDBList.class){throw new InvalidMongoDbApiUsageException("error: $and meet unknown type "+value.getClass()+" "+existing.getClass());}BasicDBList basicDBList = new BasicDBList();basicDBList.addAll((BasicDBList) existing);basicDBList.addAll((BasicDBList) value);document.put(key,basicDBList);}else{document.remove(key);Document left = new Document(key,existing);Document right = new Document(key,value);BasicDBList basicDBList = new BasicDBList();basicDBList.add(left);basicDBList.add(right);setValue(document,"$and",basicDBList);}}
}
但是我们不能直接修改包当中的源码,这里我采用的方法是新建一个类CriteriaSub,并拷贝了Criteria的部分方法,用Java的反射机制将Criteria中的私有变量读取了出来。最终实现了将Criteria生成Document的方法,并保证不会报错InvalidMongoDbApiUsageException,然后新写一个方法将Document再次还原成Criteria以便后续使用。
代码(省流,可以直接看这里)
最终所有代码如下,建立一个工具类CriteriaUtil
对于原本出错的语句,加上这一行即可
criteria = CriteriaUtil.reform(criteria);
import com.mongodb.BasicDBList;
import lombok.extern.slf4j.Slf4j;
import org.bson.Document;
import org.springframework.data.mongodb.InvalidMongoDbApiUsageException;
import org.springframework.data.mongodb.core.geo.GeoJson;
import org.springframework.data.mongodb.core.query.Criteria;
import org.springframework.data.mongodb.core.query.GeoCommand;
import org.springframework.lang.Nullable;
import org.springframework.util.CollectionUtils;
import org.springframework.util.StringUtils;import java.lang.reflect.Field;
import java.util.*;/*** @Description Criteria重构*/
public class CriteriaUtil{private static BasicDBList createCriteriaList(Collection<Criteria> criteria) {BasicDBList bsonList = new BasicDBList();for (Criteria c : criteria) {bsonList.add(c.getCriteriaObject());}return bsonList;}public static Criteria and(Criteria... criteria){return and(Arrays.asList(criteria));}public static Criteria and(Collection<Criteria> criteria) {BasicDBList bsonList = createCriteriaList(criteria);return new Criteria("$and").is(bsonList);}public static Criteria or(Criteria... criteria){return or(Arrays.asList(criteria));}public static Criteria or(Collection<Criteria> criteria){BasicDBList bsonList = createCriteriaList(criteria);return new Criteria("$or").is(bsonList);}/*** @Description: 重组criteria,解决InvalidMongoDbApiUsageException*/public static Criteria reform(Criteria criteria){try {criteria.getCriteriaObject();return criteria;} catch (InvalidMongoDbApiUsageException e) {Document document = new CriteriaSub(criteria).getCriteriaObject();return from(document);}}/*** @Description: Document 转化成 Criteria*/public static Criteria from(Document document) {Criteria c = new Criteria();try {Field _criteria = c.getClass().getDeclaredField("criteria");_criteria.setAccessible(true);@SuppressWarnings("unchecked")LinkedHashMap<String, Object> criteria = (LinkedHashMap<String, Object>) _criteria.get(c);for (Map.Entry<String, Object> set : document.entrySet()) {criteria.put(set.getKey(), set.getValue());}Field _criteriaChain = c.getClass().getDeclaredField("criteriaChain");_criteriaChain.setAccessible(true);@SuppressWarnings("unchecked")List<Criteria> criteriaChain = (List<Criteria>) _criteriaChain.get(c);criteriaChain.add(c);} catch (Exception e) {// Ignore}return c;}private static class CriteriaSub {private static Object NOT_SET = new Object();private static final int[] FLAG_LOOKUP = new int['\uffff'];@Nullableprivate String key;private List<Criteria> criteriaChain;private LinkedHashMap<String, Object> criteria = new LinkedHashMap();@Nullableprivate Object isValue;public CriteriaSub(Criteria criteria){Class<?> clazz = criteria.getClass();Field field ;try {field = clazz.getDeclaredField("NOT_SET");field.setAccessible(true);//压制java检查机制NOT_SET = field.get(criteria);field = clazz.getDeclaredField("key");field.setAccessible(true);//压制java检查机制key = (String) field.get(criteria);field = clazz.getDeclaredField("criteriaChain");field.setAccessible(true);//压制java检查机制criteriaChain = (List<Criteria>) field.get(criteria);field = clazz.getDeclaredField("criteria");field.setAccessible(true);//压制java检查机制this.criteria = (LinkedHashMap<String, Object>) field.get(criteria);field = clazz.getDeclaredField("isValue");field.setAccessible(true);//压制java检查机制isValue = field.get(criteria);} catch (NoSuchFieldException | IllegalAccessException e) {// ignore}}public Document getCriteriaObject() {if (this.criteriaChain.size() == 1) {return new CriteriaSub(this.criteriaChain.get(0)).getSingleCriteriaObject();} else if (CollectionUtils.isEmpty(this.criteriaChain) && !CollectionUtils.isEmpty(this.criteria)) {return this.getSingleCriteriaObject();} else {Document criteriaObject = new Document();for (Criteria value : this.criteriaChain) {CriteriaSub c = new CriteriaSub(value);Document document = c.getSingleCriteriaObject();for (String k : document.keySet()) {setValue(criteriaObject, k, document.get(k));}}return criteriaObject;}}protected Document getSingleCriteriaObject() {Document document = new Document();boolean not = false;for (Map.Entry<String, Object> stringObjectEntry : this.criteria.entrySet()) {String key = stringObjectEntry.getKey();Object value = stringObjectEntry.getValue();if (requiresGeoJsonFormat(value)) {value = new Document("$geometry", value);}if (not) {Document notDocument = new Document();notDocument.put(key, value);document.put("$not", notDocument);not = false;} else if ("$not".equals(key) && value == null) {not = true;} else {document.put(key, value);}}if (!StringUtils.hasText(this.key)) {if (not) {return new Document("$not", document);}return document;}Document queryCriteria = new Document();if (!NOT_SET.equals(this.isValue)) {queryCriteria.put(this.key, this.isValue);queryCriteria.putAll(document);} else {queryCriteria.put(this.key, document);}return queryCriteria;}private static boolean requiresGeoJsonFormat(Object value) {return value instanceof GeoJson || value instanceof GeoCommand && ((GeoCommand)value).getShape() instanceof GeoJson;}private static void setValue(Document document, String key, Object value) {Object existing = document.get(key);if (existing == null) {document.put(key, value);} else {if(key.equals("$and")){System.out.println("merge $and "+value+" "+ existing);if(value.getClass() != BasicDBList.class || existing.getClass() != BasicDBList.class){throw new InvalidMongoDbApiUsageException("error: $and meet unknown type "+value.getClass()+" "+existing.getClass());}BasicDBList basicDBList = new BasicDBList();basicDBList.addAll((BasicDBList) existing);basicDBList.addAll((BasicDBList) value);document.put(key,basicDBList);}else{System.out.println("merge "+key+" "+value+" "+ existing);document.remove(key);Document left = new Document(key,existing);Document right = new Document(key,value);BasicDBList basicDBList = new BasicDBList();basicDBList.add(left);basicDBList.add(right);setValue(document,"$and",basicDBList);
// throw new InvalidMongoDbApiUsageException("Due to limitations of the org.bson.Document, you can't add a second '" + key + "' expression specified as '" + key + " : " + value + "'. Criteria already contains '" + key + " : " + existing + "'.");}}}}
}