运行POST请求以在for循环中获取服务凭单

编程问答 2022-06-06

问题描述

我正在使用NIH / NLM REST API，并尝试一次以编程方式提取大量数据。我从未使用过使用服务票证（TGT和ST）而不是OAUTH进行验证的API，该API需要针对您提出的每个GET请求进行刷新，因此我不确定我是否正在正确地解决这个问题方式。非常感谢您的帮助。

这是我当前拥有的代码：

library(httr)
library(jsonlite)
library(xml2)

UTS_API_KEY <- 'MY API KEY'

# post to the CAS endpoint
response <- POST('https://utslogin.nlm.nih.gov/cas/v1/api-key',encode='form',body=list(apikey = 'MY API KEY'))

# print out the status_code and content_type
status_code(response)
headers(response)$`content-type`

doc <- content(response)
action_uri <- xml_text(xml_find_first(doc,'//form/@action'))
action_uri

# Service Ticket
response <- POST(action_uri,body=list(service = 'http://umlsks.nlm.nih.gov'))
ticket <- content(response,'text')
ticket #this is the ST I need for every GET request I make


# build search_uri using the paste function for string concatenation
version <- 'current'
search_uri <- paste('https://uts-ws.nlm.nih.gov/rest/search/',version,sep='')

# pass the the query params into httr GET to get the response 
query_string <- 'diabetic foot'
response <- GET(search_uri,query=list(ticket=ticket,string=query_string))

## print out some of the results
search_uri
status_code(response)
headers(response)$`content-type`


search_results_auto_parsed <- content(response)
search_results_auto_parsed


class(search_results_auto_parsed$result$results)

search_results_data_frame <- fromJSON(content(response,'text'))
search_results_data_frame

此代码仅适用于少数GET请求，但是，我尝试提取300多个医学术语。例如，在查询字符串中，我想遍历字符串数组（例如“糖尿病”，“血压”，“心血管护理”，“ EMT”等）。我需要发出POST请求，并将ST传递给数组中每个字符串的GET参数。

我玩过以下代码：

for (i in 1:length(Entity_Subset$Entities)){
  ent = Entity_Subset$Entities[i] #Entities represents my df of strings 
  url <- paste(' https://uts-ws.nlm.nih.gov/rest/search/current?string=',ent,'&ticket=',sep = "")
  print(url)
  }

但是在将字符串放入（GET）HTTPS请求中之后，将POST和GET请求凑在一起没有很多运气。

侧边栏：我也尝试过用Postman写一些前脚本，但是奇怪的是Service Ticket并没有以JSON的形式返回（没有键值对可以获取和传递）。只是纯文本。

感谢您提供的任何建议！

解决方法

我认为您可以将POST和GET请求都包装在一个函数中。然后，lapply可以执行字符列表。

library(httr)
library(jsonlite)
library(xml2)

fetch_data <- function(query_string = 'diabetic foot',UTS_API_KEY = 'MY API KEY',version = 'current') {
  response <- POST('https://utslogin.nlm.nih.gov/cas/v1/api-key',encode='form',body=list(apikey = UTS_API_KEY))
  
  # print out the status_code and content_type
  message(status_code(response),"\n",headers(response)$`content-type`)
  action_uri <- xml_text(xml_find_first(content(response),'//form/@action')); message(action_uri)
  
  # Service Ticket
  response <- POST(action_uri,encode = 'form',body=list(service = 'http://umlsks.nlm.nih.gov'))
  ticket <- content(response,'text'); message(ticket)
  
  # build search_uri using the paste function for string concatenation
  search_uri <- paste0('https://uts-ws.nlm.nih.gov/rest/search/',version)
  # pass the the query params into httr GET to get the response 
  response <- GET(search_uri,query=list(ticket=ticket,string=query_string))
  ## print out some of the results
  message(search_uri,status_code(response),headers(response)$`content-type`)
  fromJSON(content(response,'text'))
}

# if you have a list of query strings,then
lapply(Entity_Subset$Entities,fetch_data,UTS_API_KEY = "blah blah blah")

# The `lapply` above is logically equivalent to
result <- vector("list",length(Entity_Subset$Entities))
for (x in Entity_Subset$Entities) {
  result[[x]] <- fetch_data(x,"blah blah blah")
}
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