Delphi parse JSON array or array

Question

This is the sample JSON I want to be able to parse:

[
  {
    \"a\":{
      \"username\":\"aaa\",
      \"email\":\"         


        

Answer 1

For new readers looking for these answers.

How about this function, or even simpler if you restructure the JSON data?

function getData(JsonString: String; User: String; Field: String): String;
var
  JSonValue: TJSonValue;
  JsonArray: TJSONArray;
  ArrayElement: TJSonValue;
  FoundValue: TJSonValue;
begin
  Result :='';

  // create TJSonObject from string
  JsonValue := TJSonObject.ParseJSONValue(JsonString);

  // get the array
  JsonArray := JsonValue as TJSONArray;

  // iterate the array
  for ArrayElement in JsonArray do begin
      FoundValue := ArrayElement.FindValue(User);
      if FoundValue <> nil then begin
        Result := ArrayElement.GetValue(User + '.' + Field);
        break;
      end;
  end;
end;

The problem with the sample JSON code above is that it uses the users' names "a" "b" as a JSON-key {key:data} for the users' data. In this way you can't use GetValue("a") in your search for data. Structuring your JSON data differently makes the search process a lot easier. I will later on give an example of this.

A way to handle the given JSON data is by using FindValue so you can check if a field with key "a" or "b" exists.

FoundValue := ArrayElement.FindValue("b");
if FoundValue <> nil then begin
    Result := ArrayElement.GetValue("b"+ '.' + "email");
    break;

About the 'parsing a JSON array' question: After the data is loaded as a TJSonObject you can change the data into a TJSONArray and iterate the elements.

  JsonValue := TJSonObject.ParseJSONValue(JsonString);  
  JsonArray := JsonValue as TJSONArray;
  for ArrayElement in JsonArray do begin
    ...

A working example code for the given JSON data:

unit JsonArray1;

interface

uses System.JSON;

function getData2(JsonString: String; User: String; Field: String): String;
procedure Test1();

implementation

function getData2(JsonString: String; User: String; Field: String): String;
var
  JSonValue: TJSonValue;
  JsonArray: TJSONArray;
  ArrayElement: TJSonValue;
  FoundValue: TJSonValue;
begin
  Result :='';

  // create TJSonObject from string
  JsonValue := TJSonObject.ParseJSONValue(JsonString);

  // get the array
  JsonArray := JsonValue as TJSONArray;

  // iterate the array
  for ArrayElement in JsonArray do begin
      FoundValue := ArrayElement.FindValue(User);
      if FoundValue <> nil then begin
        Result := ArrayElement.GetValue(User + '.' + Field);
        break;
      end;
  end;
end;

procedure Test1();
var
  DataBase: String;
  EmailAddress : String;
  Username: String;
begin
  DataBase := '[  {"a" : {"username":"aaa","email":"aaa@gmail.com"}},' +
                 '{"b" : {"username":"bbb","email":"bbb@gmail.com"}}  ]';

  EmailAddress := getData2(DataBase, 'b', 'email');
  Username := getData2(DataBase, 'a', 'username');

end;

end.

As already mentioned, restructuring the JSON data with proper keys makes the code to find data more simple. Because there is a 1 on 1 relation between the users' data "a":{}, "b":{} it's easy to introduce a 'user' key. Also adding a 'users' key to the array results in all data having keys.

  '{"users" : [{ "user":"a", "username":"aaa","email":"aaa@gmail.com"},' +
              '{ "user":"b", "username":"bbb","email":"bbb@gmail.com"}]}';

When you iterate the users, you can now use GetValue with the new "user" key.

  if ArrayElement.GetValue('user') = 'b' then begin
    Result := ArrayElement.GetValue('email');

By giving the array a key you can now get the array with:

JsonArray := JsonValue.GetValue('users');

A working example code for the restructured JSON data:

unit JsonArray2;

interface

uses System.JSON;

function getData2(JsonString: String; User: String; Field: String): String;
procedure Test2();

implementation

function getData2(JsonString: String; User: String; Field: String): String;
var
  JSonValue: TJSonValue;
  JsonArray: TJSONArray;
  ArrayElement: TJSonValue;
  FoundValue: TJSonValue;
begin
  Result :='';

  // create TJSonObject from string
  JsonValue := TJSonObject.ParseJSONValue(JsonString);

  // get the array
  JsonArray := JsonValue.GetValue('users');

  // iterate the array
  for ArrayElement in JsonArray do begin
      if ArrayElement.GetValue('user') = User then begin
        Result := ArrayElement.GetValue(Field);
        break;
      end;
  end;
end;

procedure Test2();
var
  DataBase: String;
  EmailAddress : String;
  Username: String;
begin
  DataBase := '{"users" : [{ "user":"a", "username":"aaa","email":"aaa@gmail.com"},' +
                          '{ "user":"b", "username":"bbb","email":"bbb@gmail.com"}]}';

  EmailAddress := getData2(DataBase, 'b', 'email');
  Username := getData2(DataBase, 'a', 'username');

end;

end.