如何使用Java驱动程序为MongoDB构建$或查询？ [英] How can I build an $or query for MongoDB using the Java driver?

问题描述

我正在尝试使用MongoDB中的某些条件（使用Java驱动程序）。这就是我正在做的事情：

  Pattern regex = Pattern.compile（title）; 
 DBCollection coll = MongoDBUtil.getDB（）。getCollection（post_details）; 
 
 BasicDBObject query = new BasicDBObject（）; 
 query.put（category_title，myCategory）; 
 query.append（post_title，regex）; 
 query.append（post_description，regex）; 
 
 DBCursor cur = coll.find（query）; 
 while（cur.hasNext（））{
 System.out.println（cur.next（）。get（post_id））; 
} 
  

我想使用 $或这些条件下的操作数，但我猜默认是和，我不知道如何更改它。在上面的代码中，如果其中一个条件返回 null ，结果也将是 null 。

解决方案

你是正确的，在查询中指定多个字段的默认是每个字段用作条件过滤器，因此是一个AND使用具有以下语法的$或操作数，可以使用OR子句执行MongoDB查询：

  db.col.find（{$ or：[clause1，clause2]}）
  

其中每个子句都可以是查询。 $或者不必是顶级操作数，但如果是MongoDB，则可以为每个单独的子句使用索引。

在您的示例中，您希望以此结束查询：

  db.col.find（{$ or：[{post_title，regex}，{post_description，正则表达式}]}）; 
  

可以用Java构建：

  DBObject clause1 = new BasicDBObject（post_title，regex）; 
 DBObject clause2 = new BasicDBObject（post_description，regex）; 
 BasicDBList或= new BasicDBList（）; 
 or.add（clause1）; 
 or.add（第2条）; 
 DBObject query = new BasicDBObject（$ or，or）; 
  

I'm trying to Or some conditions in MongoDB (using the Java driver). This is what I'm doing :

Pattern regex = Pattern.compile("title");   
DBCollection coll = MongoDBUtil.getDB().getCollection("post_details");

BasicDBObject query = new BasicDBObject();
query.put("category_title", "myCategory");      
query.append("post_title", regex);  
query.append("post_description", regex);    

DBCursor cur = coll.find(query);
while(cur.hasNext()) {
    System.out.println(cur.next().get("post_id"));
}

I'd like to use the $or operand on these conditions, but I guess the default is "and" and I don't know how to change it. In the above code if one of the conditions returns null, the result will be null too.

解决方案

You are correct that the "default" for specifying multiple field in a query is that each field serves as a conditional filter, and thus is an AND operation.

You can perform MongoDB queries with an OR clause by using the $or operand which has the following syntax :

db.col.find({$or:[clause1, clause2]})

Where each clause can be a query. $or does not have to be a top level operand but if it is MongoDB can use an index for each seperate clause.

In your example you want to end up with this query :

db.col.find({$or:[{"post_title", regex}, {"post_description", regex}]});  

Which can be constructed in Java through :

DBObject clause1 = new BasicDBObject("post_title", regex);  
DBObject clause2 = new BasicDBObject("post_description", regex);    
BasicDBList or = new BasicDBList();
or.add(clause1);
or.add(clause2);
DBObject query = new BasicDBObject("$or", or);

这篇关于如何使用Java驱动程序为MongoDB构建$或查询？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！