R How to make a POST request to MongoDB

问题

I'm currently working with data from an online database. I access the data via API, which works when I retrieve all data at once. But this makes my system slow, so I want to make a request only for filtered data (which I did not make until now). This is the way to get the whole dataset:

#-------------------------------#
#          packages             #
#-------------------------------#
library(httr)
library(jsonlite)

#-------------------------------#
#         API requests          #
#-------------------------------#

##  get all data at once  ##
url <- "https://www.eter-project.com/api/3.0/HEIs/full"
raw_result <- GET(url)

#-------------------------------#
#       data processing         #
#-------------------------------#

# 'status_code' (if request worked) and 'content' (APIs answer) important
names(raw_result) 

# '200' tells us that server received request
raw_result$status_code 

# translate Unicode into text
this.raw.content <- rawToChar(raw_result$content) 

# transform json into workable format for R
mydata <- fromJSON(this.raw.content, flatten = TRUE) 

class(mydata)
dim(mydata)

According to the documentation (https://www.eter-project.com/api/doc/#/) I need a POST request using url https://www.eter-project.com/api/3.0/HEIs/queryand a filter embedded in the following structure:

{
 "filter": {},
  "fieldIds": {}
}

I want to filter for years and countries in order to only get the data I currently want to work with. The structure for the filter would be { "BAS.REFYEAR.v": 2011, "BAS.COUNTRY.v": "AT"}.

Has anyone an idea, how I could implement this into a POST request?

Until now, I made some desperate attempts to include the filter into the POST requests (e.g. raw_result <- POST(url, body = list({ "filter": {"BAS.REFYEAR.v" = 2011}}), encode = "json") and played around with the mongolitepackage, which was not even close.

UPDATE: the filtering problem has been solved. I used the following solution:

myquery <- '{
  "filter": {"BAS.REFYEAR.v": 2015, "BAS.COUNTRY.v": "LV"},
  "fieldIds": {},
  "searchTerms": []
  }'

url <- "https://www.eter-project.com/api/3.0/HEIs/query"

raw_result <- POST(url, body = myquery, content_type_json())

Now, I face another problem: the data include many special characters, which are not displayed properly in R (e.g. Alberta koledža in the dataset is displayed as Alberta koledÅ¾ain R). Is there a way to solve this, for example by using UTF-8 in the request call?

回答1:

You can try to build the required JSON as list of lists. However, I find it easier to supply the JSON explicitly and add the content type manually:

query <- '{
  "filter": { "BAS.REFYEAR.v": 2011,  "BAS.COUNTRY.v": "AT"},
  "fieldIds": {},
  "searchTerms": []
}'
url <- "https://www.eter-project.com/api/3.0/HEIs/query"
raw_result <- httr::POST(url = url, body = query, content_type_json())

After this you can apply your processing as before.

来源：https://stackoverflow.com/questions/53445960/r-how-to-make-a-post-request-to-mongodb

标签

json

mongodb

api

post