Question 175628 in Json Question posted in
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How do I get a nested JSON field with TClientDataset in Delphi?

I am using TRestClient>TRestRequest>TRestResponse>TRESTResponseDataSetAdapter to retrieve JSON data from a Rest API. This works well and I create a TClientDataset in memory:

  // Create a new in memory dataset
  gStaffTable := TClientDataset.Create(nil);

  with gStaffTable do
  begin
    // Add some fields to it
    FieldDefs.Add('FirstName', ftString, 255, False);         //0
    FieldDefs.Add('MiddleName', ftString, 255, False);        //1
    FieldDefs.Add('LastName', ftString, 255, False);          //2
    // ...add the other fields 3..26 here
    // Department is a nested field
    FieldDefs.Add('Department', ftString, 255, False);        //27

    // Create it
    CreateDataSet;
    // Add an AfterScroll procedure
    AfterScroll := gStaffTableAfterScroll;
    OnCalcFields := gStaffTableOnCalcFields;

    IndexFieldNames := 'FullName';
    Open;
    FieldByName('Firstname').DisplayLabel := 'First Name';
    FieldByName('MiddleName').DisplayLabel := 'Middle Name';
    //.. add the rest of the displaylabels here
 
   end;

I can then read my data into the fields:

  ClientDataset.First;
  while not ClientDataSet.EOF do
  begin
    with gStaffTable do
    begin
      try
        application.ProcessMessages;
        append;
          FieldbyName('Firstname').AsString := ClientDataSetfirst_name.AsString;
          FieldbyName('LastName').AsString := ClientDataSetlast_name.AsString;
          FieldbyName('Fullname').AsString := ClientDataSetfirst_name.AsString + ' ' + 
          //.. do the same for the rest of the fields
          
          // Department is a nested field - need to modify this to read the department name
          // {"name":"Finance","id":29111}
          FieldbyName('Department').AsString :=  ClientDataSet.FieldByName('Department').AsString;

        post;
      except

      end;
    end;
    application.ProcessMessages;
    ClientDataSet.Next;
  end;

I can then just assign the DataField to a component on the GUI (partial screen snip):

enter image description here

You can see from this what my problem is. The Department field is a nested element and I cannot figure out how to access {"name":"Finance","id":29111} to display Finance.

I have tried various resolutions to similar problems but cannot find one that works.

Tags:

2

Answers


  1. 0

    You can use the TJSONObject.ParseJSONValue class function for parsing the JSON string.

    For example, you can define a function to extract the value:

    uses
  System.JSON;

function ExtractPairStringValue(const AJSONString : string; const APairName : string) : string;
var
  Obj : TJSONValue;
begin
  Obj := TJSONObject.ParseJSONValue(AJSONString);
  try
    Result := Obj.GetValue<string>(APairName);
  finally
    Obj.Free;
  end;
end;

    Then you’ll be able to extract the value like this:

    FieldByName('Department').AsString := ExtractPairStringValue(ClientDataSet.FieldByName('Department').AsString, 'name');
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  2. 0

    Add another field to dataset "Finance" then set an TField.OnGetText event on him.

    procedure GetFinanceValue should extract data from JSON
    If you want to set value to finance make procedure to do it

    procedure TForm1.FieldOnGetText(Sender: TField; var Text: string;
  DisplayText: Boolean);
begin
    Text := GetFinanceValue(Sender);
end;

procedure TForm1.FieldOnSetText(Sender: TField; var Text: string; DisplayText: Boolean);
begin
  SetFinanceValue(sender, Text);
end;
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