Accessing JSON data from Open Weater Maps API
lazarus / 38-Networking and Web Programming

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CieloInvernale · 2016-12-19 21:41

I'm trying to interface with OpenWeaterMaps API
(http://openweathermap.org/). All API options and parameters are fully
explained, anyway I've got troubles when I came to the Lazarus part
(sorry, I'm a newbye with Lazarus...).

The application is simple: retrieve JSON data from the appropriate URL
then parse each part as a simple string.

My program 'till now tries to retrieve the "main" data in JSON
structure ("Clouds" in the following example JSON code - notice that
there are 2 different "main" nodes in the response, I'm trying to
access the first one nested within "weather" or, in other words,
"weather->main:Clouds").

JSON API's response sample:

Code: Text  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i {"coord":{"
lon":145.77,"lat":-
16.92},"weather":[{"id":803,"main":"Clouds","description":"broken
clouds","icon":"04n"}],"base":"cmc stations","main":{"temp":293.25,"pr
essure":1019,"humidity":83,"temp_min":289.82,"temp_max":295.37},"wind"
:{"speed":5.1,"deg":150},"clouds":{"all":75},"rain":{"3h":3},"dt":1435
658272,"sys":{"type":1,"id":8166,"message":0.0166,"country":"AU","sunr
ise":1435610796,"sunset":1435650870},"id":2172797,"name":"Cairns","cod
":200} 
My code so far (MYCITYID and MYAPPID are placeholders for the real
keys, obviously not to be published here...):

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
Unit1; {$mode objfpc}{$H+} interface uses  Classes, SysUtils,
FileUtil, Forms, Controls, Graphics, Dialogs, StdCtrls, fphttpclient, 
fpjson, jsonparser; type   { TForm1 }   TForm1 = class(TForm)   
Memo1: TMemo;    procedure FormCreate(Sender: TObject);  private    {
private declarations }  public    { public declarations }  end; var 
Form1: TForm1;  jData : TJSONData;  jObject : TJSONObject; 
wheater_main : String; implementation {$R *.lfm} { TForm1 } procedure
TForm1.FormCreate(Sender: TObject);begin  jData := GetJSON(TFPHTTPClie
nt.SimpleGet('http://api.openweathermap.org/data/2.5/weather?id=MYCITY
ID&appid=MYAPPID'));   wheater_main :=
jData.FindPath('main').AsString;   Memo1.Lines.Clear;  
Memo1.Lines.Add(wheater_main); end; end. 
Code compiles correctly and an executable is produced, anyway when I
launch it it returns the following error:

QuoteCannot convert data from object value.
Any idea about what's wrong with my code??

Thanks in advance for your time and attention.

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molly · 2016-12-20 00:15

The path main is not a complete end path, rather a path to a more
complex (sub)structure in json format.

Either access the full path directly by supplying that full path (e.g.
"main.pressure") or retrieve path "main" into a separate JSONData
structure (jData2 := jData.FindPath('main')) and then search for the
path e.g. "pressure").

edit: if your aim is really to get a string representation of the main
json data structure then you can use jData.FindPath('main').AsJSon;

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bytebites · 2016-12-20 04:10

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
jData.FindPath('weather').Items[0].FindPath('main').AsString

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molly · 2016-12-20 04:31

Ah, good point bytebites.

 I overlooked that there were multiple "main"'s 

In that case:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
Writeln('weather[0].main = ' ,
jData.FindPath('weather[0].main').AsString);

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magleft · 2023-09-29 10:06

I tried downloading data from openweathermap. The raw data is in the
form shown below:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i {"cod":"200
","message":0,"cnt":40,"list":[{"dt":1695988800,"main":{"temp":300.37,
"feels_like":300.12,"temp_min":300.37,"temp_max":301.04,"pressure":101
8,"sea_level":1018,"grnd_level":1015,"humidity":39,"temp_kf":-
0.67},"weather":[{"id":500,"main":"Rain","description":"light rain","i
con":"10d"}],"clouds":{"all":31},"wind":{"speed":3.12,"deg":231,"gust"
:2.49},"visibility":10000,"pop":0.22,"rain":{"3h":0.17},"sys":{"pod":"
d"},"dt_txt":"2023-09-29 12:00:00"},{"dt":1695999600,"main":{"temp":29
7.16,"feels_like":297.13,"temp_min":295.72,"temp_max":297.16,"pressure
":1018,"sea_level":1018,"grnd_level":1016,"humidity":58,"temp_kf":1.44
},"weather":[{"id":500,"main":"Rain","description":"light rain","icon"
:"10d"}],"clouds":{"all":41},"wind":{"speed":2.08,"deg":357,"gust":4.8
},"visibility":10000,"pop":0.71,"rain":{"3h":1.47},"sys":{"pod":"d"},"
dt_txt":"2023-09-29 15:00:00"},{"dt":1696010400,"main":{"temp":291.93,
"feels_like":292,"temp_min":291.93,"temp_max":291.93,"pressure":1019,"
sea_level":1019,"grnd_level":1017,"humidity":82,"temp_kf":0},"weather"
:[{"id":501,"main":"Rain","description":"moderate rain","icon":"10n"}]
,"clouds":{"all":54},"wind":{"speed":2.85,"deg":15,"gust":4.62},"visib
ility":10000,"pop":0.9,"rain":{"3h":3.45},"sys":{"pod":"n"},"dt_txt":"
2023-09-29 18:00:00"},{"dt":1696021200,"main":{"temp":292.09,"feels_li
ke":292.02,"temp_min":292.09,"temp_max":292.09,"pressure":1019,"sea_le
vel":1019,"grnd_level":1017,"humidity":76,"temp_kf":0},"weather":[{"id
":500,"main":"Rain","description":"light rain","icon":"10n"}],"clouds"
:{"all":38},"wind":{"speed":1.82,"deg":57,"gust":2.37},"visibility":10
000,"pop":0.6,"rain":{"3h":0.16},"sys":{"pod":"n"},"dt_txt":"2023-09-
29 21:00:00"},{"dt":1696032000,"main":{"temp":292.82,"feels_like":292.
72,"temp_min":292.82,"temp_max":292.82,"pressure":1018,"sea_level":101
8,"grnd_level":1016,"humidity":72,"temp_kf":0},"weather":[{"id":803,"m
ain":"Clouds","description":"broken clouds","icon":"04n"}],"clouds":{"
all":68},"wind":{"speed":1.55,"deg":21,"gust":1.54},"visibility":10000
,"pop":0.34,"sys":{"pod":"n"},"dt_txt":"2023-09-30 00:00:00"},{"dt":16
96042800,"main":{"temp":292.45,"feels_like":292.32,"temp_min":292.45,"
temp_max":292.45,"pressure":1017,"sea_level":1017,"grnd_level":1015,"h
umidity":72,"temp_kf":0},"weather":[{"id":500,"main":"Rain","descripti
on":"light rain","icon":"10n"}],"clouds":{"all":100},"wind":{"speed":1
.55,"deg":35,"gust":1.52},"visibility":10000,"pop":0.37,"rain":{"3h":0
.11},"sys":{"pod":"n"},"dt_txt":"2023-09-30 03:00:00"}, 
I tried the following code without success:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i   Http :=
TFPHTTPClient.Create(nil);   try     Http.IOTimeout := 1000;   
 Http.AllowRedirect := True;     jData := GetJSON(Http.Get(urltext)); 
   Memo1.Lines.Add(jData.FindPath('list.items[0].main.items.temp').AsS
tring);    Json.Free;   finally     Http.Free;   end;  
Can anyone help?

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paweld · 2023-09-29 10:25

In your case, the path should look like this:Code: Pascal
 [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
Memo1.Lines.Add(jData.FindPath('list[0].main.temp').AsString);clearer
example:Code: Pascal  [Select][+][-]window.onload = function(){var x1
= document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i uses 
fpjson; procedure TForm1.Button1Click(Sender: TObject);const  json = '
{"cod":"200","message":0,"cnt":40,"list":[{"dt":1695988800,"main":{"te
mp":300.37,"feels_like":300.12,"temp_min":300.37,"temp_max":301.04,"pr
essure":1018,"sea_level":1018,"grnd_level":1015,"humidity":39,"temp_kf
":-0.67},"weather":[{"id":500,"main":"Rain","description":"light rain"
,"icon":"10d"}],"clouds":{"all":31},"wind":{"speed":3.12,"deg":231,"gu
st":2.49},"visibility":10000,"pop":0.22,"rain":{"3h":0.17},"sys":{"pod
":"d"},"dt_txt":"2023-09-29 12:00:00"},{"dt":1695999600,"main":{"temp"
:297.16,"feels_like":297.13,"temp_min":295.72,"temp_max":297.16,"press
ure":1018,"sea_level":1018,"grnd_level":1016,"humidity":58,"temp_kf":1
.44},"weather":[{"id":500,"main":"Rain","description":"light rain","ic
on":"10d"}],"clouds":{"all":41},"wind":{"speed":2.08,"deg":357,"gust":
4.8},"visibility":10000,"pop":0.71,"rain":{"3h":1.47},"sys":{"pod":"d"
},"dt_txt":"2023-09-29 15:00:00"},{"dt":1696010400,"main":{"temp":291.
93,"feels_like":292,"temp_min":291.93,"temp_max":291.93,"pressure":101
9,"sea_level":1019,"grnd_level":1017,"humidity":82,"temp_kf":0},"weath
er":[{"id":501,"main":"Rain","description":"moderate rain","icon":"10n
"}],"clouds":{"all":54},"wind":{"speed":2.85,"deg":15,"gust":4.62},"vi
sibility":10000,"pop":0.9,"rain":{"3h":3.45},"sys":{"pod":"n"},"dt_txt
":"2023-09-29 18:00:00"},{"dt":1696021200,"main":{"temp":292.09,"feels
_like":292.02,"temp_min":292.09,"temp_max":292.09,"pressure":1019,"sea
_level":1019,"grnd_level":1017,"humidity":76,"temp_kf":0},"weather":[{
"id":500,"main":"Rain","description":"light rain","icon":"10n"}],"clou
ds":{"all":38},"wind":{"speed":1.82,"deg":57,"gust":2.37},"visibility"
:10000,"pop":0.6,"rain":{"3h":0.16},"sys":{"pod":"n"},"dt_txt":"2023-
09-29 21:00:00"},{"dt":1696032000,"main":{"temp":292.82,"feels_like":2
92.72,"temp_min":292.82,"temp_max":292.82,"pressure":1018,"sea_level":
1018,"grnd_level":1016,"humidity":72,"temp_kf":0},"weather":[{"id":803
,"main":"Clouds","description":"broken clouds","icon":"04n"}],"clouds"
:{"all":68},"wind":{"speed":1.55,"deg":21,"gust":1.54},"visibility":10
000,"pop":0.34,"sys":{"pod":"n"},"dt_txt":"2023-09-30 00:00:00"},{"dt"
:1696042800,"main":{"temp":292.45,"feels_like":292.32,"temp_min":292.4
5,"temp_max":292.45,"pressure":1017,"sea_level":1017,"grnd_level":1015
,"humidity":72,"temp_kf":0},"weather":[{"id":500,"main":"Rain","descri
ption":"light rain","icon":"10n"}],"clouds":{"all":100},"wind":{"speed
":1.55,"deg":35,"gust":1.52},"visibility":10000,"pop":0.37,"rain":{"3h
":0.11},"sys":{"pod":"n"},"dt_txt":"2023-09-30 03:00:00"}]}';var  jd:
TJSONData;  ja: TJSONArray;  jo: TJSONObject;  i: Integer;begin  jd :=
GetJSON(json);  if jd.FindPath('list') <> nil then  begin    ja :=
TJSONArray(jd.FindPath('list'));    if ja.Count > 0 then    begin    
jo := TJSONObject(ja.Items[0]);      if jo.FindPath('main.temp') <>
nil then        Memo1.Lines.Add(Format('%5d     %f', [i,
jo.FindPath('main.temp').AsFloat]));    end;    ////or all items   
//for i := 0 to ja.Count - 1 do    //begin    //  jo :=
TJSONObject(ja.Items[i]);    //  if jo.FindPath('main.temp') <> nil
then    //    Memo1.Lines.Add(Format('%5d     %f', [i,
jo.FindPath('main.temp').AsFloat]));    //end;  end;  jd.Free;end;

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TRon · 2023-09-29 10:31

Also note that you get a list of 40! entries. It is a forecast based
upon this. I have no idea if the data in the list is sorted in a
particular order (I assume it is returned with a sort on dt values).

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magleft · 2023-09-29 11:39

Indeed, it concerns 40 registrations. I modified the example paweld
sent a bit, but it doesn't work. What am I doing wrong;

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TFwheather.Button2Click(Sender: TObject);var  Http: TFPHTTPClient; 
info, Content: string;  Json: TJSONData;  JsonObject: TJSONObject; 
wheater_main : String;  jdata:TJSONData;  enum: TJSONEnum;  jd:
TJSONData;  ja: TJSONArray;  jo: TJSONObject;  i: Integer;  urltext
:String;begin  urltext:='api.openweathermap.org/data/2.5/forecast?lat=
39.1520282768&lon=20,9768486023&APPID=45a17f4586f55c714ae04d9c36e8a834
' ;//{API key}  try  Http.IOTimeout := 1000;  Http.AllowRedirect :=
True;  jd := GetJSON(Http.Get(urltext));  if jd.FindPath('list') <>
nil then  begin    ja := TJSONArray(jd.FindPath('list'));    if
ja.Count > 0 then {   begin      jo := TJSONObject(ja.Items[0]);     
if jo.FindPath('main.temp') <> nil then       
Memo1.Lines.Add(Format('%5d     %f', [i,
jo.FindPath('main.temp').AsFloat]));    end;}    ////or all items   
for i := 0 to ja.Count - 1 do    begin      jo :=
TJSONObject(ja.Items[i]);      if jo.FindPath('main.temp') <> nil
then        Memo1.Lines.Add(Format('%5d     %f', [i,
jo.FindPath('main.temp').AsFloat]));    end;  end;   finally 
jd.Free;  end;end;

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rvk · 2023-09-29 11:48

Quote from: magleft on September 29, 2023, 01:39:20 pmIndeed, it
concerns 40 registrations. I modified the example paweld sent a bit,
but it doesn't work. What am I doing wrong;Well. The first thing you
are doing wrong is not telling us what the problem is 
Error message????? Crash????
What does happen?

Second... looking at your code... I see a http declaration in the
procedure but I don't see you creating the object itself.
So you are missing a
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i http :=
TFPHTTPClient.Create(nil);try  //...finally  http.free;end; 
Also... urltext needs to contain a protocol (so https:// in front of
it).

And don't forget to include opensslsockets in your uses.

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paweld · 2023-09-29 12:11

First of all, don't share your API key - they can block your
access.Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i uses 
fpjson, fphttpclient, opensslsockets; procedure
TForm1.Button1Click(Sender: TObject);const  url = 'https://api.openwea
thermap.org/data/2.5/forecast?lat=39.1520282768&lon=20,9768486023&APPI
D={yourAPPID}';var  jd: TJSONData;  ja: TJSONArray;  jo: TJSONObject; 
i: Integer;  hc: TFPHttpClient;  json: String;begin  hc :=
TFPHttpClient.Create(nil);  hc.AllowRedirect := True;  try    json :=
hc.Get(url);    if json <> '' then    begin      jd := GetJSON(json); 
    if jd.FindPath('list') <> nil then      begin        ja :=
TJSONArray(jd.FindPath('list'));        for i := 0 to ja.Count - 1 do 
      begin          jo := TJSONObject(ja.Items[i]);          if
jo.FindPath('main.temp') <> nil then           
Memo1.Lines.Add(Format('%5d     %f', [i,
jo.FindPath('main.temp').AsFloat]));        end;      end;     
jd.Free;    end    else      ShowMessage('Empty response');  finally 
 hc.Free;  end;end;

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magleft · 2023-09-29 12:22

I would like to apologize as the code was not working due to my
mistake. Due to an error in the url I didn't have the prefix '
https://'. Now all works.
Thank you all for your help.