如何使用 Java 驱动程序为 MongoDB 构建 $or 查询? [英] How can I build an $or query for MongoDB using the Java driver?
问题描述
我正在尝试或 MongoDB 中的某些条件(使用 Java 驱动程序).这就是我正在做的:
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"));
}
我想在这些条件下使用 $or
操作数,但我猜默认是and",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
,结果也会是null
.
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.
推荐答案
您是正确的,在查询中指定多个字段的默认"是每个字段都用作条件过滤器,因此是 AND 运算.
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.
您可以使用具有以下语法的 $or 操作数使用 OR 子句执行 MongoDB 查询:
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]})
其中每个子句都可以是一个查询.$or 不必是顶级操作数,但如果是,MongoDB 可以为每个单独的子句使用索引.
Where each clause can be a query. $or does not have to be a top level operand but if it is MongoDB can use an index for each seperate clause.
在您的示例中,您希望以这个查询结束:
In your example you want to end up with this query :
db.col.find({$or:[{"post_title", regex}, {"post_description", regex}]});
可以通过以下方式在 Java 中构建:
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);
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