rmongodb:在查询中使用$ or [英] rmongodb: using $or in query

问题描述

我正在努力在R和rmongodb中使用$ or创建查询.我要模拟的是来自cmdline mongo的:

I'm struggling to create a query using $or within R and rmongodb. What I'd like to emulate is this from cmdline mongo:

db.people.find( { $or : [ {"person.cell": { $exists : true } }, {"person.home": { $exists : true } } ] })

我想提取其中person.cell不为null或person.home不为null的记录.我可以分别查询每个对象，但是当我使用$ or在rmongodb中创建缓冲区时，无法获取数据，使用rmongodb的R代码如下所示:

I'd like to pull records where either person.cell is not null, or person.home is not null. I can query each individually, but cannot get data back when I create the buffer in rmongodb with the $or, the R code using rmongodb looks like this:

l <- list("$exists"="true")
buf <- mongo.bson.buffer.create()
mongo.bson.buffer.start.array(buf, "$or")
mongo.bson.buffer.append.list(buf, "person.cell", l)
mongo.bson.buffer.append.list(buf, "person.home", l)
mongo.bson.buffer.finish.object(buf)  
b <- mongo.bson.from.buffer(buf)
mongo.find(mongo, "work.people", b)

不返回任何记录，没有错误，只是一个空集.如前所述，我可以在person.cell或person.home上进行查找并获取结果，但是当我尝试执行$ or(在rmongodb中)以使我可以使用person.cell或person.home提取记录时，则无法获取结果.

That returns no records, no error, just an empty set. As I mentioned, I can do a find on either person.cell or person.home and get results, but not when I try to do an $or (in rmongodb) so that I pull records with either person.cell or person.home.

我也尝试过:

buf <- mongo.bson.buffer.create()
mongo.bson.buffer.start.array(buf, "$or")
mongo.bson.buffer.start.object(buf, "person.cell")
mongo.bson.buffer.append(buf, "$exists", "true")
mongo.bson.buffer.finish.object(buf)
mongo.bson.buffer.start.object(buf, "person.home")
mongo.bson.buffer.append(buf, "$exists", "true")
mongo.bson.buffer.finish.object(buf)
mongo.bson.buffer.finish.object(buf)
b <- mongo.bson.from.buffer(buf)
mongo.find(mongo, "work.people", b)

但是我得到了相同的空集结果(当我查看它时，"b"看起来是一样的).我被困在这一个.

But I get the same empty set result (and "b" looks the same when I view it). I'm stuck on this one.

推荐答案

为避免不得不编写mongo.bson.buffer-statements序列，我编写了一个程序包(

To avoid having to compose the sequence of mongo.bson.buffer-statements I wrote a package (rmongodbHelper) that will translate a JSON or a list() to a BSON object which can then be used with rmongodb.

首先让我们设置环境:

library(rmongodb)

# install rmongodbHelper package from GitHub

library(devtools)
devtools::install_github("joyofdata/rmongodbHelper")
library(rmongodbHelper)

# the MongoDB instance

ns <- "dbx.collx"
M <- mongo.create()
mongo.is.connected(M)
mongo.remove(M, ns, json_to_bson("{}"))

# inserting a number of dummy objects
# JSON keys currently are expected to be wrapped in double quotes!

objs <- c(
  '{"_id":-1}',
  '{"_id":-2, "person":{}}',
  '{"_id":-3, "person":{"x":0}}',
  '{"_id":1,  "person":{"cell":0}}',
  '{"_id":2,  "person":{"home":0}}',
  '{"_id":3,  "person":{"cell":0,"home":0}}'
)

for(obj in objs) {
  mongo.insert(M, ns, json_to_bson(obj))
}

让我们通过MongoDB shell看一下是否成功插入了它们:

Let's see via MongoDB shell if they were successfully inserted:

> use dbx
switched to db dbx
> db.collx.find().pretty()
{ "_id" : -1 }
{ "_id" : -2, "person" : { } }
{ "_id" : -3, "person" : { "x" : 0 } }
{ "_id" : 1, "person" : { "cell" : 0 } }
{ "_id" : 2, "person" : { "home" : 0 } }
{ "_id" : 3, "person" : { "cell" : 0, "home" : 0 } }

现在让我们通过查询来搜索文档:

Now let's search for documents with a query:

# searching for those objects
# JSON keys currently are expected to be wrapped in double quotes!

json_qry <- 
'{
  "$or" : [ 
    {"person.cell": { "$exists" : true } }, 
    {"person.home": { "$exists" : true } } 
  ] 
}'

cur <- mongo.find(M, "dbx.collx", json_to_bson(json_qry))

while(mongo.cursor.next(cur)) {
    print(mongo.cursor.value(cur))
}

这就是我们最终得到的:

And this is what we get in the end:

_id : 1      1.000000
person : 3   
    cell : 1     0.000000

_id : 1      2.000000
person : 3   
    home : 1     0.000000

_id : 1      3.000000
person : 3   
    cell : 1     0.000000
    home : 1     0.000000

这篇关于rmongodb:在查询中使用$ or的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！