下面的bson是personaddress
集合:
{
"id" : "123456",
"name" : "foo",
"address" : [
{
"local" : "yes",
"location" : [
{
"place" : {
"_id":"VZG",
},
"place_lat" : "18",
"place_lan" : "83",
},
{
"place" : {
"name" : "kerala",
"district" : "palakkad",
"pincode" : "5203689",
},
"place_lat" : "18",
"place_lan" : "83",
}
]
}
]
}
我有另一个 places
集合:
{
"_id":"VZG",
"name" : "vizag",
"district" : "Visakhaptanam,
"pincode" : "568923",
}
在 mongodb 聚合中使用查找,我想将 places
集合嵌入到 personaddress
集合中
我试过用
Aggregation aggregation = newAggregation(lookup("places", "address.location.place._id", "_id", "myplaces"), unwind("myplaces"));
AggregationResults<OutputDocument> aggResults = mongoTemplate.aggregate(aggregation, PersonAddressDocument.class, OutputDocument.class);
谁能帮帮我?
最佳答案
因为你有嵌套数组,你需要应用 $unwind
运算符,以便在使用 $lookup
之前对嵌入文档进行非规范化 管道(除非您已经在聚合操作中将它们展平):
db.personaddress.aggregate([
{ "$unwind": "$address" },
{ "$unwind": "$address.location" },
{
"$lookup": {
"from": "places",
"localField": "address.location.place._id",
"foreignField": "_id",
"as": "address.location.place",
}
}
])
然后可以实现为(未测试):
LookupOperation lookupOperation = LookupOperation.newLookup()
.from("places")
.localField("address.location.place._id")
.foreignField("_id")
.as("address.location.place");
Aggregation agg = newAggregation(
unwind("address"),
unwind("address.location"),
lookupOperation
);
AggregationResults<OutputDocument> aggResults = mongoTemplate.aggregate(
agg, PersonAddressDocument.class, OutputDocument.class
);
如果您的 Spring Data 版本不支持此功能,解决方法是实现 AggregationOperation 接受 DBObject
的接口(interface):
public class CustomGroupOperation implements AggregationOperation {
private DBObject operation;
public CustomGroupOperation (DBObject operation) {
this.operation = operation;
}
@Override
public DBObject toDBObject(AggregationOperationContext context) {
return context.getMappedObject(operation);
}
}
然后执行 $lookup
在聚合管道中作为 DBObject 操作:
DBObject lookupOperation = (DBObject)new BasicDBObject(
"$lookup", new BasicDBObject("from", "places")
.append("localField", "address.location.place._id")
.append("foreignField", "_id")
.append("as", "address.location.place")
);
然后您可以将其用作:
Aggregation agg = newAggregation(
unwind("address"),
unwind("address.location"),
lookupOperation
);
AggregationResults<OutputDocument> aggResults = mongoTemplate.aggregate(
agg, PersonAddressDocument.class, OutputDocument.class
);
关于java - 在 mongodb 聚合中查找,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/41243746/