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我正在查询包含示例中显示的条目的数据库。所有条目都包含以下值：

  • _idoverallitem:和的唯一标识placed_items
  • name: 你的名字overallitem
  • loc:overallitem和的位置placed_items
  • time_id:overallitem存储时间
  • placed_items：包含数组placed_items（范围可以从零：placed_items : [],到无限量。
  • category_id: 的类别placed_items
  • full_id: 的完整 idplaced_items

我想在给定和约束的每个级别上提取name,full_id和category_idplaced_itemstime_idloc

示例数据：

{
 "_id" : "5040",
 "name" : "entry1",
 "loc" : 1,
 "time_id" : 20121001,
 "placed_items" : [],
}
{
 "_id" : "5041",
 "name" : "entry2",
 "loc" : 1,
 "time_id" : 20121001,
 "placed_items" : [
  {
   "_id" : "5043",
   "category_id" : 101,
   "full_id" : 901,
  },
  {
   "_id" : "5044",
   "category_id" : 102,
   "full_id" : 902,
  }
 ],
}
{
 "_id" : "5042",
 "name" : "entry3",
 "loc" : 1,
 "time_id" : 20121001,
 "placed_items" : [
  {
   "_id" : "5045",
   "category_id" : 101,
   "full_id" : 903,
  },
 ],
}

此示例的预期结果是：

"name"    "full_id" "category_id"
"entry2"    901         101
"entry2"    902         102
"entry3"    903         101

因此，如果placed_items为空，请将条目放入数据框中，如果placed_items包含n条目，则将n条目放入数据框中

我试图制定一个 RBlogger 示例来创建所需的数据框。

#Set up database
    mongo <- mongo.create()

    #Set up condition
    buf <- mongo.bson.buffer.create()
    mongo.bson.buffer.append(buf, "loc", 1)
    mongo.bson.buffer.start.object(buf, "time_id")
    mongo.bson.buffer.append(buf, "$gte", 20120930)
    mongo.bson.buffer.append(buf, "$lte", 20121002)
    mongo.bson.buffer.finish.object(buf)
    query <- mongo.bson.from.buffer(buf)

    #Count  
    count <- mongo.count(mongo, "items_test.overallitem", query) 

#Note that these counts don't work, since the count should be based on 
#the number of placed_items in the array, and not the number of entries. 

    #Setup Cursor
    cursor <- mongo.find(mongo, "items_test.overallitem", query)
    #Create vectors, which will be filled by the while loop
    name <- vector("character", count)
    full_id<- vector("character", count)
    category_id<- vector("character", count) 

    i <- 1
    #Fill vectors
    while (mongo.cursor.next(cursor)) {
        b <- mongo.cursor.value(cursor)
        order_id[i] <- mongo.bson.value(b, "name")
        product_id[i] <- mongo.bson.value(b, "placed_items.full_id")
        category_id[i] <- mongo.bson.value(b, "placed_items.category_id")
        i <- i + 1
    }
    #Convert to dataframe
    results <- as.data.frame(list(name=name, full_id=full_uid, category_id=category_id))

如果我想在某个overallitem级别（即_idor name）提取值但无法收集placed_items级别上的信息，则条件有效并且代码有效。此外，提取的虚线调用full_id似乎category_id不起作用。任何人都可以帮忙吗？

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