MongoDB Java错误:管道阶段规范对象必须恰好包含一个字段
MongoDB Java错误:管道阶段规范对象必须恰好包含一个字段
提问于 2021-03-30 02:09:15
我正在尝试在java上获取这个MongoDB查询的结果。
db.fileTree.aggregate([
{
$match: {
"_id": "6062144bb25e4809548ef246",
}
},
{
$unwind: "$children"
},
{
$match: {
"children.fileName": "Test1"
}
},
{
$project: {
"_id": 0,
"fileId": "$children.fileId",
"fileName": "$children.fileName",
"directory": "$children.directory",
}
}
]).pretty()查询运行得非常好，当没有数据时，它不会显示任何内容。但是，当从java执行查询时，会产生以下错误：
com.mongodb.MongoCommandException: Command failed with error 40323 (Location40323): 'A pipeline stage specification object must contain exactly one field.' on server localhost:27017. The full response is {"ok": 0.0, "errmsg": "A pipeline stage specification object must contain exactly one field.", "code": 40323, "codeName": "Location40323"}
ChildFile findChildInParent(String parentId, String fileName) {
BasicDBObject idFilter = new BasicDBObject().append("_id", parentId);
BasicDBObject matchId = new BasicDBObject().append("$match", idFilter);
BasicDBObject unwindChildren = new BasicDBObject().append("$unwind", "$children");
BasicDBObject childNameFilter = new BasicDBObject().append("children.fileName", fileName);
BasicDBObject matchChildName = new BasicDBObject().append("$match", childNameFilter);
BasicDBObject projections = new BasicDBObject()
.append("_id", 0)
.append("fileId", "$children.fileId")
.append("fileName", "$children.fileName")
.append("directory", "$children.directory");
List<ChildFile> childFiles = fileCollection.aggregate(
List.of(matchId, unwindChildren, matchChildName, projections),
ChildFile.class
).into(new ArrayList<>());
return childFiles.size() > 0 ? childFiles.get(0) : null;
}我是不是漏掉了什么？任何帮助都是非常感谢的。谢谢你，?！
回答 1
Stack Overflow用户
回答已采纳
发布于 2021-03-30 02:25:11
您的代码中有一个拼写错误，缺少children字段的$
应该是：
BasicDBObject unwindChildren = new BasicDBObject().append("$unwind", "$children")而不是：
BasicDBObject unwindChildren = new BasicDBObject().append("$unwind", "children")还缺少$poject阶段：
BasicDBObject projections = new BasicDBObject()
.append("_id", 0)
.append("fileId", "$children.fileId")
.append("fileName", "$children.fileName")
.append("directory", "$children.directory");
BasicDBObject projectionStage = new BasicDBObject().append("$project", projections);
List<ChildFile> childFiles = fileCollection.aggregate(
List.of(matchId, unwindChildren, matchChildName, projectionStage),
ChildFile.class
).into(new ArrayList<>());页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/66859375
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