Parsing JSON using Delphi 7

Question

I have a JSON file which I need to parse to extract some values.

A sample looks like this:

[
  {
    "period": "2016-06-07 - 2016-06-14",
    "range": "2016-06-07..2016-06-14",
    "items": [
      {
        "region_name": "Canterbury/Otago",
        "region_id": 12,
        "average_cover": 2099,
        "average_growth": 16,
        "reading_count": 3
      },
      {
        "region_name": "Southland",
        "region_id": 14,
        "average_cover": 2068,
        "average_growth": 3,
        "reading_count": 1
      },
      {
        "region_name": "Wairarapa \u0026 Hawkes Bay",
        "region_id": 10,
        "average_cover": 2195,
        "average_growth": 20,
        "reading_count": 2
      }
    ]
  },
  {
    "period": "2016-05-31 - 2016-06-07",
    "range": "2016-05-31..2016-06-07",
    "items": [
      {
        "region_name": "Canterbury/Otago",
        "region_id": 12,
        "average_cover": 2126,
        "average_growth": 17,
        "reading_count": 5
      },
      {
        "region_name": "Southland",
        "region_id": 14,
        "average_cover": 2181,
        "average_growth": 10,
        "reading_count": 2
      }
    ]
  },
  {
    "period": "2016-05-24 - 2016-05-31",
    "range": "2016-05-24..2016-05-31",
    "items": [
      {
        "region_name": "Canterbury/Otago",
        "region_id": 12,
        "average_cover": 2139,
        "average_growth": 28,
        "reading_count": 6
      },
      {
        "region_name": "Central Plateau",
        "region_id": 6,
        "average_cover": 2400,
        "average_growth": 38,
        "reading_count": 1
      },
      {
        "region_name": "Wairarapa \u0026 Hawkes Bay",
        "region_id": 10,
        "average_cover": 2254,
        "average_growth": 27,
        "reading_count": 2
      }
    ]
  },
  {
    "period": "2016-05-18 - 2016-05-25",
    "range": "2016-05-18..2016-05-25",
    "items": [
      {
        "region_name": "Canterbury/Otago",
        "region_id": 12,
        "average_cover": 2183,
        "average_growth": 39,
        "reading_count": 6
      },
      {
        "region_name": "Manawatu",
        "region_id": 9,
        "average_cover": 2315,
        "average_growth": 42,
        "reading_count": 1
      },
      {
        "region_name": "Wairarapa \u0026 Hawkes Bay",
        "region_id": 10,
        "average_cover": 2228,
        "average_growth": 29,
        "reading_count": 2
      }
    ]
  },
  {
    "period": "2016-05-10 - 2016-05-17",
    "range": "2016-05-10..2016-05-17",
    "items": [
      {
        "region_name": "Canterbury/Otago",
        "region_id": 12,
        "average_cover": 2251,
        "average_growth": 40,
        "reading_count": 8
      },
      {
        "region_name": "Otago",
        "region_id": 13,
        "average_cover": 2595,
        "average_growth": 26,
        "reading_count": 1
      },
      {
        "region_name": "Southland",
        "region_id": 14,
        "average_cover": 2526,
        "average_growth": 49,
        "reading_count": 2
      },
      {
        "region_name": "Waikato",
        "region_id": 4,
        "average_cover": 2484,
        "average_growth": 60,
        "reading_count": 1
      },
      {
        "region_name": "Wairarapa \u0026 Hawkes Bay",
        "region_id": 10,
        "average_cover": 2201,
        "average_growth": 34,
        "reading_count": 2
      }
    ]
  }
]

The items I am looking to extract are region_id, average_cover, and average_growth.

I have succeeded in extracting the values from the first items array, but my sample JSON file contains 4 items arrays and I can only seem to extract the values from the first items element.

I have been using the ulkJSON.pas library and my Delphi code looks like this to send the values to a TMemo on a form:

var 
  js: TlkJSONBase;
  Items: TlkJSONbase;
  I: Integer;
  lHTTP: TIdHTTP;
  sJSON: String;      
begin
  sJSON :=  // as per sample JSON text in question
  js := TlkJSON.ParseText(sJSON);
  Items := js.Field['items'];
  for I := 0 to Pred(Items.Count) do begin
    Memo1.Lines.Add(VarToStr(Items.Child[I].Field['region_id'].Value));
    Memo1.Lines.Add(VarToStr(Items.Child[I].Field['average_cover'].Value));
    Memo1.Lines.Add(VarToStr(Items.Child[I].Field['average_growth'].Value));
  end;
end;

I tried formatting your JSON code for you, but it's apparently not valid JSON. EDIT Actually you forgot to include the opening / closing array brackets ([]). However, even with that, either way I don't see how you could be reading the items object the way your code is written. — Jerry Dodge
– Jerry Dodge, Commented Jun 15, 2016 at 20:50
I reformatted the JSON to make the arrays a little clearer. But yes, the code does not match the JSON shown. — Remy Lebeau
– Remy Lebeau, Commented Jun 15, 2016 at 22:16

Remy Lebeau · Accepted Answer · 2016-06-15 22:31:41Z

6

You are not taking the top-level array into account. This code works for the JSON shown:

var 
  sJSON: String;      
  js, Items, Item: TlkJSONBase;
  I, J: Integer;
begin
  sJSON :=  // as per sample JSON text in question
  js := TlkJSON.ParseText(sJSON);
  for I := 0 to Pred(js.Count) do
  begin
    Items := js.Child[I].Field['items'];
    for J := 0 to Pred(Items.Count) do begin
      Item := Items.Child[J];
      Memo1.Lines.Add(VarToStr(Item.Field['region_id'].Value));
      Memo1.Lines.Add(VarToStr(Item.Field['average_cover'].Value));
      Memo1.Lines.Add(VarToStr(Item.Field['average_growth'].Value));
    end;
  end;
end;

answered Jun 15, 2016 at 22:31

Remy Lebeau

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1 Comment

DaveMc Over a year ago

That's great. Worked perfectly. Also the error with my original JSON sample text. Much appreciated.

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