Delphi: Accessing JSON Objects within a JSON Array - sql

Question

I have a JSON Object, let's name it jObject that looks like this:
{
"id": 0,
"data": "[{DAT_INCL: \"08/03/2012 10:07:08\", NUM_ORDE: 1, NUM_ATND: 1, NUM_ACAO: 2, NUM_RESU: 3},
{DAT_INCL: \"08/03/2012 10:07:09\", NUM_ORDE: 2, NUM_ATND: 1, NUM_ACAO: 4, NUM_RESU: 5},
{DAT_INCL: \"08/03/2012 10:07:09\", NUM_ORDE: 3, NUM_ATND: 1, NUM_ACAO: 8, NUM_RESU: NULL}]"
}
As you can see, it contains two pairs, one of which is an array with three objects in this case (the amount of objects is dynamic) with multiple "key: values"(these don't vary, being always the same 5 fields), which I want to insert into an SQL database, "key" being column, "value" being field. Question is, how do I access each object individually?
Code-wise what I did was extract the pair that contained this array by putting it in jPair
jPair := OriginalObject.Get(1);
and then captured the array
jArray:= TJSONArray(jPair.JsonValue);
(Also, as a bonus, when I evaluate jArray.Size, the result is 6226004. What?)

Answer 1

If you have an array from DBXJSON, then it is a TJSONArray. Call its Get method to get an element of the array.
var
Value: TJSONValue;
Value := jArray.Get(0);
You can also go through the entire array with a for loop:
for Value in jArray do
But if you check the Size property and get 6226004 instead of 3, that suggests there's something else wrong here. My guess is that what you think is a TJSONArray isn't really that type. Use as to do a checked type cast:
jArray := jPair.JsonValue as TJSONArray;
You'll get an EInvalidCast exception if that fails.

Answer 2

here is an sample code to parse and output your json data. I've modified your JSON data and added ArrayData field, wich contains your initial array of objects:
program Project1;
{$APPTYPE CONSOLE}
{$R *.res}
uses
System.SysUtils, dbxjson;
const JSON_DATA = '{"ArrayData":['+
'{"DAT_INCL":"07/03/2012 17:33:03", "NUM_ORDE":1,"NUM_ATND":1, "NUM_ACAO":2, "NUM_RESU":3},'+
'{"DAT_INCL":"07/03/2012 17:33:05", "NUM_ORDE":2,"NUM_ATND":1, "NUM_ACAO":4, "NUM_RESU":5},'+
'{"DAT_INCL":"07/03/2012 17:33:05", "NUM_ORDE":3,"NUM_ATND":1, "NUM_ACAO":8, "NUM_RESU":null}'+
']}';
var jsv : TJsonValue;
originalObject : TJsonObject;
jsPair : TJsonPair;
jsArr : TJsonArray;
jso : TJsonObject;
i : integer;
begin
try
//parse json string
jsv := TJSONObject.ParseJSONValue(JSON_DATA);
try
//value as object
originalObject := jsv as TJsonObject;
//get pair, wich contains Array of objects
jspair := originalObject.Get('ArrayData');
//pair value as array
jsArr := jsPair.jsonValue as TJsonArray;
writeln('array size: ', jsArr.Size);
//enumerate objects in array
for i := 0 to jsArr.Size - 1 do begin
writeln('element ', i);
// i-th object
jso := jsArr.Get(i) as TJsonObject;
//enumerate object fields
for jsPair in jso do begin
writeln(' ', jsPair.JsonString.Value, ': ', jsPair.JsonValue.Value);
end;
end;
finally
jsv.Free();
readln;
end;
except
on E: Exception do
Writeln(E.ClassName, ': ', E.Message);
end;
end.

Answer 3

Practical example of adding JSON data from an array to a TComboBox
This example assumes you have included the JSON unit. It also assumes you have a TComboBox named cmbCompany. There is nothing wrong with the accepted answers, I just wanted to document.
uses JSON;
procedure LoadCompanies;
var
i : Integer;
companyArray : TJsonArray;
company : TJsonObject;
begin
//get the company data
companyData := TJSONObject.ParseJSONValue('{data:[{"name": "One"},{"name": "Two"}]}') as TJSONObject;
try
cmbCompany.Items.Clear;
with companyData do
begin
//Important bit which relates to the question!
companyArray := (Get('data').JsonValue as TJSONArray);
try
for i := 0 to companyArray.Size-1 do
begin
//Get one of the array values
company := (companyArray.Get(i) as TJSONObject);
//Add name to combo box, you can obviously get other values in similar fashion
cmbCompany.Items.Add(company.GetValue<String>('name'));
end;
finally
companyArray.Free;
end;
end;
finally
companyData.Free;
end;
end;