如何在Spring中编写mongo聚合减少查询? [英] How do I write mongo aggregation reduce query in Spring?
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问题描述
mongo中的数据:
data in mongo :
db.test2.aggregate([
{
"$project" : {
"contents" : 1,
"comments" : {
"$filter" : {
"input" : "$comments",
"as" : "item",
"cond" : {"$gt" : ['$$item.score', 2]}
},
},
"comments2" : {
"$filter" : {
"input" : "$comments2",
"as" : "item",
"cond" : {"$gt" : ["$$item.score", 5]}
}
}
}
},
{
"$project" : {
"content" : 1,
"commentsTotal" : {
"$reduce" : {
"input" : "$comments",
"initialValue" : 0,
"in" : {"$add" : ["$$value", "$$this.score"]}
}
},
"comments2Total" : {
"$reduce" : {
"input" : "$comments2",
"initialValue" : 0,
"in" : {"$add" : ["$$value", "$$this.score"]}
}
}
}
},
{$skip : 0},
{$limit: 3}
]);
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所以您可以看到,它执行以下操作: 1,过滤评论和评论2,得分≥5. 2,在评论数组中计算总数.
So you can see, this does the following : 1、filter the comments and comments2 which score is gt 5. 2、count total of the socre in comment array.
我这样在Spring中编写聚合查询:
and i write the aggregation query in Spring like this:
AggregationExpression reduce = ArithmeticOperators.Add.valueOf("$$value").add("$$this.socre");
Aggregation aggregation = Aggregation.newAggregation(
Aggregation.project().andExclude("_id")
.andInclude("content")
.and("comments").filter("item", ComparisonOperators.Gt.valueOf("item.score").greaterThanValue(3)).as("comments")
.and("comments2").filter("item", ComparisonOperators.Gt.valueOf("item.score").greaterThanValue(3)).as("comments2"),
Aggregation.project("comments", "comments2")
.and(ArrayOperators.Reduce.arrayOf("comments").withInitialValue("0").reduce(reduce)).as("commentsTotal")
);
当我跑起来时,它会抛出异常:
when i run like up , it will throws exception :
java.lang.IllegalArgumentException:无效的引用'$$ value'!
java.lang.IllegalArgumentException: Invalid reference '$$value'!
推荐答案
您可以通过将$filter
包装在$reduce
操作中来尝试以下聚合.
You can try below aggregation by wrapping $filter
inside the $reduce
operation.
类似下面的内容
AggregationExpression reduce1 = new AggregationExpression() {
@Override
public DBObject toDbObject(AggregationOperationContext aggregationOperationContext) {
DBObject filter = new BasicDBObject("$filter", new BasicDBObject("input", "$comments").append("as", "item").append("cond",
new BasicDBObject("$gt", Arrays.<Object>asList("$$item.score", 2))));
DBObject reduce = new BasicDBObject("input", filter).append("initialValue", 0).append("in", new BasicDBObject("$add", Arrays.asList("$$value", "$$this.socre")));
return new BasicDBObject("$reduce", reduce);
}
};
Aggregation aggregation = newAggregation(
Aggregation.project().andExclude("_id")
.andInclude("content")
.and(reduce1).as("commentsTotal")
);
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