MongoDB聚合条件转换为JAVA驱动程序

Question

I'm relatively new to MongoDB and I'm currently working with java towards a "find by most tags matching" solution to information within a collection.

I'm stuck now trying to translate a MongoDB shell operation to the JAVA driver version (this sintaxis is part of the definitions needed )

$cond:[{$eq: ["$tags", 200]}, 1, 0]

What would be a correct JAVA implementation for the sentence above?

Thank you in advance

Answer 1

Whatever the $cond object where in your aggregation operation, to build it to should do something like this:

BasicDBList eqList = new BasicDBList();
eqList.add("$tags");
eqList.add(200);

DBObject eqObject = BasicDBObjectBuilder.start()
    .add("$eq", eqList)
    .get();

BasicDBList condList = new BasicDBList();
condList.add(eqObject);
condList.add(1);
condList.add(0);

DBObject condObject = BasicDBObjectBuilder.start()
    .add("$cond", condList)
    .get();

I'm confusing about your aggregation operation, could you give more details?