Question

我試圖在R.

查詢從 Materials Project web API數據

的文檔提供其使用兩個curl和python進行的示例性查詢。我已經複製下面的curl命令。

curl -s --header "X-API-KEY: <YOUR-API-KEY>" \ 
    https://materialsproject.org/rest/v2/query \ 
    -F criteria='{"elements": {"$in": ["Li", "Na", "K"], "$all": ["O"]}, "nelements": 2}' \ 
    -F properties='["formula", "formation_energy_per_atom"]' 

從閱讀httr quickstart guide，在我看來，我應該能夠重現此查詢有：

library(httr) 
POST(url = "https://www.materialsproject.org/rest/v2/query", 
    config = add_headers("X-API-KEY" = "<YOUR-API-KEY>",  
    body = list(criteria = "{'elements': {'$in': ['Li', 'Na', 'K'], '$all': ['O']}, 'nelements': 2}", 
       properties = "['formula', 'formation_energy_per_atom']"), 
    encode = "multipart", 
    verbose()) 

不過，雖然curl命令，從材料項目數據庫返回JSON數據，我R查詢返回HTTP/1.1 400 BAD REQUEST。在上面的代碼中，捲曲的做法與httr不同嗎？

我已經嘗試將-v放在curl上，並將其與上面的（verbose()）輸出進行比較，但是curl沒有顯示它在多部分形式中的含義。

> Expect: 100-continue 
> Content-Type: multipart/form-data; boundary=------------------------d2ef2f3982185118 
> 
< HTTP/1.1 100 Continue 
< HTTP/1.1 200 OK 
< Date: Tue, 27 Dec 2016 21:18:58 GMT 
< Server: Apache/2.2.15 (CentOS) 
< Vary: Accept-Encoding,User-Agent 
< Connection: close 
< Transfer-Encoding: chunked 
< Content-Type: application/json 

同時httr顯示：

-> Content-Type: multipart/form-data; boundary=----------------------------5b4873dbc9cd 
-> 
<- HTTP/1.1 100 Continue 
>> ------------------------------5b4873dbc9cd 
>> Content-Disposition: form-data; name="criteria" 
>> 
>> {'elements': {'$in': ['Li', 'Na', 'K'], '$all': ['O']}, 'nelements': 2} 
>> ------------------------------5b4873dbc9cd 
>> Content-Disposition: form-data; name="properties" 
>> 
>> ['formula', 'formation_energy_per_atom'] 
>> ------------------------------5b4873dbc9cd-- 

Answer 1

這確實是一個可怕的，未經深思熟慮&懶洋洋地實現API。他們似乎喜歡Python，所以這不會讓人感到意外。

以下工作：

library(httr) 
library(jsonlite) 

list(
    criteria=toJSON(list(
    elements=list(
     `$in`=c("Li", "Na", "K"), 
     `$all`=c("0") 
    ), 
    nelements=unbox(2) 
)), 
    properties=toJSON(c("formula", "formation_energy_per_atom")) 
) -> params 

POST(url="https://www.materialsproject.org/rest/v2/query", 
    add_headers(`X-API-KEY`=Sys.getenv("MATERIALS_PROJECT_API_KEY")), 
    body=params, 
    encode="multipart", verbose()) -> res 

和這裏的verbose()輸出來證明這一點：

-> POST /rest/v2/query HTTP/1.1 
-> Host: www.materialsproject.org 
-> User-Agent: libcurl/7.51.0 r-curl/2.3 httr/1.2.1 
-> Accept-Encoding: gzip, deflate 
-> Accept: application/json, text/xml, application/xml, */* 
-> X-API-KEY: wouldntyouliketoknow 
-> Content-Length: 344 
-> Expect: 100-continue 
-> Content-Type: multipart/form-data; boundary=------------------------34f08173ce0a7818 
-> 
<- HTTP/1.1 100 Continue 
>> --------------------------34f08173ce0a7818 
>> Content-Disposition: form-data; name="criteria" 
>> 
>> {"elements":{"$in":["Li","Na","K"],"$all":["0"]},"nelements":2} 
>> --------------------------34f08173ce0a7818 
>> Content-Disposition: form-data; name="properties" 
>> 
>> ["formula","formation_energy_per_atom"] 
>> --------------------------34f08173ce0a7818-- 

<- HTTP/1.1 200 OK 
<- Date: Wed, 28 Dec 2016 02:08:08 GMT 
<- Server: Apache/2.2.15 (CentOS) 
<- Vary: Accept-Encoding,User-Agent 
<- Content-Encoding: gzip 
<- Content-Length: 258 
<- Connection: close 
<- Content-Type: application/json 
<- 

這是超級挑剔的查詢字符串結構。他們真的應該接受一個JSON體，並且已經完成了它。但是，一半刪減是蟒民間的方式。

哦，天哪，我只注意到它是提供回覆的CentOS服務器。是的。那些人真的很喜歡痛苦。