How to parse JSON in Delphi? - json

Question

I have a JSON like this:
{
"Content": [{
"Identifier": "AABBCC",
"Description": "test terfdfg",
"GenericProductIdentifier": "AABBCC",
"ProductFamilyDescription": "sampling",
"LifeCycleStatus": "ACTIVE",
"Price": {
"Value": 1.00,
"Quantity": 1000
},
"LeadTimeWeeks": "16",
"FullBoxQty": 200,
}],
"TotalElements": 1,
"TotalPages": 1,
"NumberOfElements": 1,
"First": true,
"Size": 1,
"Number": 0
}
In Delphi 10.4, I'm trying to parse it, but I can't access the values ​​contained in 'Price'.
I wrote code like this:
var
vContent: TJSONArray;
vJson: TJSONObject;
vContentRow: TJSONObject;
i,j : Integer;
begin
Memo2.Lines.Clear;
if Memo1.Text = '' then
exit;
vJson := TJSONObject(TJSONObject.ParseJSONValue(TEncoding.ASCII.GetBytes(Memo1.Text),0));
try
vContent := TJSONArray(vJson.Get('Content').JsonValue);
for i := 0 to Pred(vContent.Count) do
begin
vContentRow := TJSONObject(vContent.Items[i]);
for j := 0 to Pred(vContentRow.Count) do
begin
Memo2.Lines.Add(' '+ vContentRow.Get(j).JsonString.Value+' : '+ vContentRow.Get(j).JsonValue.Value);
end;
end;
Memo2.Lines.Add(vContent.Value);
finally
end;
end;
What is the correct way to read the values ​​contained in 'Price'?

Answer 1

Here is a sample code to parse your JSON:
uses
System.IOUtils, System.JSON, System.Generics.Collections;
procedure TForm1.Button1Click(Sender: TObject);
procedure GetPrices(const S: string);
var
V: TJsonValue;
O, E, P: TJsonObject;
A: TJsonArray;
begin
V := TJSONObject.ParseJSONValue(S);
if not Assigned(V) then
raise Exception.Create('Invalid JSON');
try
O := V as TJSONObject;
A := O.GetValue<TJsonArray>('Content');
for var I := 0 to A.Count - 1 do
begin
E := A.Items[I] as TJsonObject; // Element
P := E.GetValue<TJsonObject>('Price');
ShowMessage('Value: ' + P.GetValue<string>('Value') + ' ' + 'Quantity: ' + P.GetValue<string>('Quantity'));
end;
finally
V.Free;
end;
end;
var
S: string;
begin
S := TFile.ReadAllText('d:\json.txt'); // Retrieve it using some webservice
GetPrices(S);
end;
Note, your JSON is invalid, the corect definition is:
{
"Content": [{
"Identifier": "AABBCC",
"Description": "test terfdfg",
"GenericProductIdentifier": "AABBCC",
"ProductFamilyDescription": "sampling",
"LifeCycleStatus": "ACTIVE",
"Price": {
"Value": 1.00,
"Quantity": 1000
},
"LeadTimeWeeks": "16",
"FullBoxQty": 200
}],
"TotalElements": 1,
"TotalPages": 1,
"NumberOfElements": 1,
"First": true,
"Size": 1,
"Number": 0
}

Answer 2

You can use the JSON library of Delphi.
The JSON library has the JsonToObject class function that can convert directly the string to an Object (Object structure)
See this:
https://docwiki.embarcadero.com/Libraries/Sydney/en/REST.Json.TJson.JsonToObject
You can create the classes structure manually o using the web: https://jsontodelphi.com/
The classes structure for your JSON created is this:
type
TPrice = class;
TPrice = class
private
FQuantity: Integer;
FValue: Double;
published
property Quantity: Integer read FQuantity write FQuantity;
property Value: Double read FValue write FValue;
end;
TContent = class
private
FDescription: string;
FFullBoxQty: Integer;
FGenericProductIdentifier: string;
FIdentifier: string;
FLeadTimeWeeks: string;
FLifeCycleStatus: string;
FPrice: TPrice;
FProductFamilyDescription: string;
published
property Description: string read FDescription write FDescription;
property FullBoxQty: Integer read FFullBoxQty write FFullBoxQty;
property GenericProductIdentifier: string read FGenericProductIdentifier write FGenericProductIdentifier;
property Identifier: string read FIdentifier write FIdentifier;
property LeadTimeWeeks: string read FLeadTimeWeeks write FLeadTimeWeeks;
property LifeCycleStatus: string read FLifeCycleStatus write FLifeCycleStatus;
property Price: TPrice read FPrice;
property ProductFamilyDescription: string read FProductFamilyDescription write FProductFamilyDescription;
public
constructor Create;
destructor Destroy; override;
end;
TRoot = class(TJsonDTO)
private
[JSONName('Content'), JSONMarshalled(False)]
FContentArray: TArray<TContent>;
[GenericListReflect]
FContent: TObjectList<TContent>;
FFirst: Boolean;
FNumber: Integer;
FNumberOfElements: Integer;
FSize: Integer;
FTotalElements: Integer;
FTotalPages: Integer;
function GetContent: TObjectList<TContent>;
protected
function GetAsJson: string; override;
published
property Content: TObjectList<TContent> read GetContent;
property First: Boolean read FFirst write FFirst;
property Number: Integer read FNumber write FNumber;
property NumberOfElements: Integer read FNumberOfElements write FNumberOfElements;
property Size: Integer read FSize write FSize;
property TotalElements: Integer read FTotalElements write FTotalElements;
property TotalPages: Integer read FTotalPages write FTotalPages;
public
destructor Destroy; override;
end;
Now, the code for parse elements is more simple. You only need a code like this to access different properties of your structure:
var
Root: TRoot;
begin
root := TJSON.JsonToObject<TRoot>(Memo1.Lines.Text);
lblid.Caption := 'TotalElements: ' + Root.TotalElements.ToString;
lblvalue.Caption := 'TotalPages: ' + Root.TotalPages.ToString;
lblcount.Caption := 'Identifier: ' + Root.Content[0].Identifier;
lblfirstonclick.Caption := 'Description: ' + Root.Content[0].Description;
lbllastonclick.Caption := 'Price/Quantity:' + Root.Content[0].Price.Quantity.ToString;
//...

Answer 3

Try this, i make some helper for TFDMemtable. Simple to uses, no need parsing everytime you have other JSON.
const
JSONString =
'{
"Content": [{
"Identifier": "AABBCC",
"Description": "test terfdfg",
"GenericProductIdentifier": "AABBCC",
"ProductFamilyDescription": "sampling",
"LifeCycleStatus": "ACTIVE",
"Price": {
"Value": 1.00,
"Quantity": 1000
},
"LeadTimeWeeks": "16",
"FullBoxQty": 200,
}],
"TotalElements": 1,
"TotalPages": 1,
"NumberOfElements": 1,
"First": true,
"Size": 1,
"Number": 0
}';
begin
if not Memtable.FillDataFromString(JSONString) then begin
ShowMessages(Memtable.FieldByName('messages').AsString);
end else begin
Memtable.FillDataFromString(Memtable.FieldByName('Content').AsString);
ShowMessages(Memtable.FieldByName('Price').AsString);
end;
end;
====
unit BFA.Helper.MemTable;
interface
uses
System.SysUtils, System.Types, System.UITypes, System.Classes, System.Variants,
FMX.Types, FMX.Controls, FMX.Forms, FMX.Graphics, FMX.Dialogs, FMX.Memo.Types,
System.Rtti, FMX.Grid.Style, FMX.Grid, FMX.ScrollBox, FMX.Memo, FMX.Edit,
FMX.Controls.Presentation, FMX.StdCtrls, FireDAC.Stan.Intf,
FireDAC.Stan.Option, FireDAC.Stan.Param, FireDAC.Stan.Error, FireDAC.DatS,
FireDAC.Phys.Intf, FireDAC.DApt.Intf, System.Net.URLClient,
System.Net.HttpClient, System.Net.HttpClientComponent, Data.DB,
FireDAC.Comp.DataSet, FireDAC.Comp.Client, System.JSON, System.Net.Mime;
type
TFDMemTableHelper = class helper for TFDMemTable
procedure FillError(FMessage, FError : String);
function FillDataFromString(FJSON : String) : Boolean; //ctrl + shift + C
end;
implementation
{ TFDMemTableHelper }
function TFDMemTableHelper.FillDataFromString(FJSON: String): Boolean; //bug memoryleak fix at checking is Object / array soon
const
FArr = 0;
FObj = 1;
FEls = 2;
function isCheck(FString : String) : Integer; begin
Result := FEls;
var FCheck := TJSONObject.ParseJSONValue(FJSON);
if FCheck is TJSONObject then
Result := FObj
else if FCheck is TJSONArray then
Result := FArr;
FCheck.DisposeOf;
end;
var
JObjectData : TJSONObject;
JArrayJSON : TJSONArray;
JSONCheck : TJSONValue;
begin
var FResult := isCheck(FJSON);
try
Self.Active := False;
Self.Close;
Self.FieldDefs.Clear;
if FResult = FObj then begin
JObjectData := TJSONObject.ParseJSONValue(FJSON) as TJSONObject;
end else if FResult = FArr then begin
JArrayJSON := TJSONObject.ParseJSONValue(FJSON) as TJSONArray;
JObjectData := TJSONObject(JArrayJSON.Get(0));
end else begin
Self.FillError('FAILED PARSING JSON', 'THIS IS NOT JSON');
Result := False;
Exit;
end;
for var i := 0 to JObjectData.Size - 1 do begin
Self.FieldDefs.Add(
StringReplace(JObjectData.Get(i).JsonString.ToString, '"', '', [rfReplaceAll, rfIgnoreCase]),
ftString,
100000,
False
);
end;
Self.CreateDataSet;
Self.Active := True;
Self.Open;
try
if FResult = FArr then begin
for var i := 0 to JArrayJSON.Size - 1 do begin
JObjectData := TJSONObject(JArrayJSON.Get(i));
Self.Append;
for var ii := 0 to JObjectData.Size - 1 do begin
JSONCheck := TJSONObject.ParseJSONValue(JObjectData.GetValue(Self.FieldDefs[ii].Name).ToJSON);
if JSONCheck is TJSONObject then
Self.Fields[ii].AsString := JObjectData.GetValue(Self.FieldDefs[ii].Name).ToJSON
else if JSONCheck is TJSONArray then
Self.Fields[ii].AsString := JObjectData.GetValue(Self.FieldDefs[ii].Name).ToJSON
else
Self.Fields[ii].AsString := JObjectData.Values[Self.FieldDefs[ii].Name].Value;
JSONCheck.DisposeOf;
end;
Self.Post;
end;
end else begin
Self.Append;
for var ii := 0 to JObjectData.Size - 1 do begin
JSONCheck := TJSONObject.ParseJSONValue(JObjectData.GetValue(Self.FieldDefs[ii].Name).ToJSON);
if JSONCheck is TJSONObject then
Self.Fields[ii].AsString := JObjectData.GetValue(Self.FieldDefs[ii].Name).ToJSON
else if JSONCheck is TJSONArray then
Self.Fields[ii].AsString := JObjectData.GetValue(Self.FieldDefs[ii].Name).ToJSON
else
Self.Fields[ii].AsString := JObjectData.Values[Self.FieldDefs[ii].Name].Value;
JSONCheck.DisposeOf;
end;
Self.Post;
end;
Result := True;
except
on E : Exception do begin
Result := False;
Self.FillError('Error Parsing JSON', E.Message);
end;
end;
finally
if FResult = FObj then
JObjectData.DisposeOf;
if FResult = FArr then
JArrayJSON.DisposeOf;
Self.First;
end;
end;
procedure TFDMemTableHelper.FillError(FMessage, FError : String);
begin
Self.Active := False;
Self.Close;
Self.FieldDefs.Clear;
Self.FieldDefs.Add('status', ftString, 200, False);
Self.FieldDefs.Add('messages', ftString, 200, False);
Self.FieldDefs.Add('data', ftString, 200, False);
Self.CreateDataSet;
Self.Active := True;
Self.Open;
Self.Append;
Self.Fields[0].AsString := FError;
Self.Fields[1].AsString := FMessage;
Self.Post;
end;
end.