Parse Json String

grantful · June 3, 2023

I am working with an api to get some data.

https://vpic.nhtsa.dot.gov/api/vehicles/decodevin/1G1BE5SM8J7207504?format=json&modelyear

So when i post to this and get the returned info as json i need to pull out the Results

I have used the Delphi Rest Debuggr and i see the info i need when i choose the string and press apply

I have copied the components to my project and when i right click the memory table and choose edit Dataset.

I see the jason string with the Results

How can i drill down to

{
"Value": "CHRYSLER",
"ValueId": "477",
"Variable": "Make",
"VariableId": 26
},
{
"Value": "CHRYSLER DE MEXICO TOLUCA",
"ValueId": "1002",
"Variable": "Manufacturer Name",
"VariableId": 27
},
{
"Value": "PT Cruiser",
"ValueId": "3595",
"Variable": "Model",
"VariableId": 28
},
{
"Value": "2003",
"ValueId": "",
"Variable": "Model Year",
"VariableId": 29
},

Thanks for any help i have never wroked with Json before

Thanks for any help.

programmerdelphi2k · June 3, 2023

uses System.JSON;

procedure YourProcedure;
var
  jsonArray: TJSONArray;
  jsonObject: TJSONObject;
begin
  jsonArray := TJSONArray.Create;
  
  // Add each object to the JSON array
  jsonObject := TJSONObject.Create;
  jsonObject.AddPair('Value', 'CHRYSLER');
  jsonObject.AddPair('ValueId', '477');
  jsonObject.AddPair('Variable', 'Make');
  jsonObject.AddPair('VariableId', '26');
  jsonArray.AddElement(jsonObject);

  jsonObject := TJSONObject.Create;
  jsonObject.AddPair('Value', 'CHRYSLER DE MEXICO TOLUCA');
  jsonObject.AddPair('ValueId', '1002');
  jsonObject.AddPair('Variable', 'Manufacturer Name');
  jsonObject.AddPair('VariableId', '27');
  jsonArray.AddElement(jsonObject);

  jsonObject := TJSONObject.Create;
  jsonObject.AddPair('Value', 'PT Cruiser');
  jsonObject.AddPair('ValueId', '3595');
  jsonObject.AddPair('Variable', 'Model');
  jsonObject.AddPair('VariableId', '28');
  jsonArray.AddElement(jsonObject);

  jsonObject := TJSONObject.Create;
  jsonObject.AddPair('Value', '2003');
  jsonObject.AddPair('ValueId', '');
  jsonObject.AddPair('Variable', 'Model Year');
  jsonObject.AddPair('VariableId', '29');
  jsonArray.AddElement(jsonObject);

  // Convert the JSON array to a string
  ShowMessage(jsonArray.ToString);

  jsonArray.Free;
end;

here you had a JSONArray with 4 elements. each element has 4 pairs (key:value). some like this. now see on help to "Get" the values

for i := 0 to jsonArray.Count - 1 do
  begin
    jsonObject := jsonArray.Items[i] as TJSONObject;
    if jsonObject.GetValue('Variable').Value = 'Model' then
    begin
      // Found the object with "Model" variable, get the "Value" value
      ShowMessage(jsonObject.GetValue('Value').Value);
      Break;
    end;
  end;

grantful · June 3, 2023

Hey thanks for the great example.

I will look at this later.

mytbo · June 3, 2023

7 hours ago, grantful said:

How can i drill down to

With mORMot you can do it very easy.

uses
  mormot.core.base,
  mormot.core.json,
  mormot.net.client;
  
type
  TDataRec = packed record
    Count: Integer;
    Message: RawUtf8;
    SearchCriteria: RawUtf8;
    Results: array of record
      Value: RawUtf8;
      ValueId: Integer;
      Variable: RawUtf8;
      VariableId: Integer;
    end;
  end;
  
var url: RawUtf8 := 'https://vpic.nhtsa.dot.gov/api/vehicles/decodevin/1G1BE5SM8J7207504?format=json&amp;modelyear';
var content: RawByteString := HttpGet(url);
if content <> '' then
begin
  var dataRec: TDataRec;
  if RecordLoadJson(dataRec, content, TypeInfo(TDataRec)) then
  begin
    ShowMessage(dataRec.Count.ToString);
    ShowMessage(Length(dataRec.Results).ToString);
    for var i: Integer := 0 to High(dataRec.Results) do
    begin
      if dataRec.Results[i].Variable = 'Crash Imminent Braking (CIB)' then
        ShowMessage(dataRec.Results[i].VariableId.ToString);
    end;
  end;
end;

Additional information can be found in this article in Delphi-PRAXIS forum. Here is the translation into English with Google Translator. The result is not perfect (rather not so good), also some formatting is destroyed, but it is readable.

With best regards

Thomas

grantful · June 3, 2023

59 minutes ago, mytbo said:

With mORMot you can do it very easy.


uses
  mormot.core.base,
  mormot.core.json,
  mormot.net.client;
  
type
  TDataRec = packed record
    Count: Integer;
    Message: RawUtf8;
    SearchCriteria: RawUtf8;
    Results: array of record
      Value: RawUtf8;
      ValueId: Integer;
      Variable: RawUtf8;
      VariableId: Integer;
    end;
  end;
  
var url: RawUtf8 := 'https://vpic.nhtsa.dot.gov/api/vehicles/decodevin/1G1BE5SM8J7207504?format=json&amp;modelyear';
var content: RawByteString := HttpGet(url);
if content <> '' then
begin
  var dataRec: TDataRec;
  if RecordLoadJson(dataRec, content, TypeInfo(TDataRec)) then
  begin
    ShowMessage(dataRec.Count.ToString);
    ShowMessage(Length(dataRec.Results).ToString);
    for var i: Integer := 0 to High(dataRec.Results) do
    begin
      if dataRec.Results[i].Variable = 'Crash Imminent Braking (CIB)' then
        ShowMessage(dataRec.Results[i].VariableId.ToString);
    end;
  end;
end;

Additional information can be found in this article in Delphi-PRAXIS forum. Here is the translation into English with Google Translator. The result is not perfect (rather not so good), also some formatting is destroyed, but it is readable.

With best regards

Thomas

Thanks very much for the help. I will look at this.

grantful · June 11, 2023

On 6/3/2023 at 4:26 PM, mytbo said:

With mORMot you can do it very easy.


uses
  mormot.core.base,
  mormot.core.json,
  mormot.net.client;
  
type
  TDataRec = packed record
    Count: Integer;
    Message: RawUtf8;
    SearchCriteria: RawUtf8;
    Results: array of record
      Value: RawUtf8;
      ValueId: Integer;
      Variable: RawUtf8;
      VariableId: Integer;
    end;
  end;
  
var url: RawUtf8 := 'https://vpic.nhtsa.dot.gov/api/vehicles/decodevin/1G1BE5SM8J7207504?format=json&amp;modelyear';
var content: RawByteString := HttpGet(url);
if content <> '' then
begin
  var dataRec: TDataRec;
  if RecordLoadJson(dataRec, content, TypeInfo(TDataRec)) then
  begin
    ShowMessage(dataRec.Count.ToString);
    ShowMessage(Length(dataRec.Results).ToString);
    for var i: Integer := 0 to High(dataRec.Results) do
    begin
      if dataRec.Results[i].Variable = 'Crash Imminent Braking (CIB)' then
        ShowMessage(dataRec.Results[i].VariableId.ToString);
    end;
  end;
end;

Additional information can be found in this article in Delphi-PRAXIS forum. Here is the translation into English with Google Translator. The result is not perfect (rather not so good), also some formatting is destroyed, but it is readable.

With best regards

Thomas

Thanks for your help.

I have one compiler error i can not figure out.

[dcc32 Error] MainTab.pas(124): E2026 Constant expression expected

var
Form3: TForm3;
url: RawUtf8 = 'https://vpic.nhtsa.dot.gov/api/vehicles/decodevin/1G1BE5SM8J7207504?format=json&modelyear';
content: RawByteString = HttpGet(url); <<<<<<<<<<<<<<<Here at this line is the error.

Thanks for helping me with this

grantful · June 11, 2023

I have changed the code to

procedure TForm1.SpeedButton1Click(Sender: TObject);
begin
const content: RawByteString = HttpGet(url);
if content <> '' then
begin
var dataRec: TDataRec;
if RecordLoadJson(dataRec, content, TypeInfo(TDataRec)) then
begin
ShowMessage(dataRec.Count.ToString);
ShowMessage(Length(dataRec.Results).ToString);
for var i: Integer := 0 to High(dataRec.Results) do
begin
if dataRec.Results.Variable = 'Crash Imminent Braking (CIB)' then
ShowMessage(dataRec.Results.VariableId.ToString);
end;
end;
end;

end;

it seems to work

grantful · June 11, 2023

The mormot solution only works for windows 😞

grantful · June 11, 2023

I can show the tubular data in the memorytable

uJasonDataModule.RESTRequest1.Execute();
 edtModel.Text := uJasonDataModule.FDMemTable1.FieldByName('Results').AsString;

How can i get to the info in the results json ?

{
    "Count": 136,
    "Message": "Results returned successfully. NOTE: Any missing decoded values should be interpreted as NHTSA does not have data on the specific variable. Missing value should NOT be interpreted as an indication that a feature or technology is unavailable for a vehicle.",
    "SearchCriteria": "VIN:1gt125e85df163635",
    "Results": [
        {
            "Value": "",
            "ValueId": "",
            "Variable": "Suggested VIN",
            "VariableId": 142
        },
        {
            "Value": "1",
            "ValueId": "1",
            "Variable": "Error Code",
            "VariableId": 143
        },
        {
            "Value": "",
            "ValueId": "",
            "Variable": "Possible Values",
            "VariableId": 144
        },
        {
            "Value": null,
            "ValueId": "",
            "Variable": "Additional Error Text",
            "VariableId": 156
        },
        {
            "Value": "1 - Check Digit (9th position) does not calculate properly",
            "ValueId": "",
            "Variable": "Error Text",
            "VariableId": 191
        },
        {
            "Value": "1GT125E8*DF",
            "ValueId": "",
            "Variable": "Vehicle Descriptor",
            "VariableId": 196
        },
        {
            "Value": null,
            "ValueId": null,
            "Variable": "Destination Market",
            "VariableId": 10
        },
        {
            "Value": "GMC",
            "ValueId": "472",
            "Variable": "Make",
            "VariableId": 26
        },
        {
            "Value": "GENERAL MOTORS LLC",
            "ValueId": "984",
            "Variable": "Manufacturer Name",
            "VariableId": 27
        },
        {
            "Value": "Sierra",
            "ValueId": "1857",
            "Variable": "Model",
            "VariableId": 28
        },
        {
            "Value": "2013",
            "ValueId": "",
            "Variable": "Model Year",
            "VariableId": 29
        },

This is what i am getting with

uJasonDataModule.RESTRequest1.Execute();
  edtModel.Text := uJasonDataModule.FDMemTable1.FieldByName('Results').AsString;

Any help is greatly. appreciated

Edited June 11, 2023 by grantful

programmerdelphi2k · June 12, 2023

@grantful

a FDMemTable can load data from many type, including JSON.

you can understand "that ARRAY" in your JSON as been a "table", then if exists an array into another array, is as a Master-Detail relationship. you see?

in your REST Debugger you can determinate "what the root", or be "where" you desire get the data on JSON result... look at on results tab... later this, just copy/paste the components for your project...

JSON root Element =

RESULTs[ 0 ]

Results[ 0 ].TableABC

https://docwiki.embarcadero.com/RADStudio/Alexandria/en/REST_Debugger_Tool

what it would be "get info"?

Edited June 12, 2023 by programmerdelphi2k

programmerdelphi2k · June 12, 2023

here a sample to convert a JSON to Dataset

uses
  REST.Response.Adapter, System.JSON;
 
procedure JsonToDataset(aDataset : TDataSet; aJSON : string);
var
  JObj: TJSONArray;
  vConv : TCustomJSONDataSetAdapter;
begin
  if (aJSON = EmptyStr) then
  begin
    Exit;
  end;
 
  JObj := TJSONObject.ParseJSONValue(aJSON) as TJSONArray;
  vConv := TCustomJSONDataSetAdapter.Create(Nil);
 
  try
    vConv.Dataset := aDataset;
    vConv.UpdateDataSet(JObj);
  finally
    vConv.Free;
    JObj.Free;
  end;
end;

Quote


JsonToDataset(FDMemTable1, My_JSON);

Edited June 12, 2023 by programmerdelphi2k

grantful · June 12, 2023

@programmerdelphi2k

Thanks for your patience and help.

I will study this.

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