使用DELPHI原生类实现数据集和JSON相互转换

 JSON二要素：数组和对象。对象可以包含数组，数组可以包含对象。无层数限制。OLEVARIANT也类似，OLEVARIANT的一个元素又可以是OLEVARIANT，且无层数限制。XML亦类似。这也是它们能序列一切对象的奥秒所在。

JSON就是字符串，定义好序列后的字符串格式，甚至都不需要啥JSON类库，就可以自行组装JSON字符串和解析JSON字串获取数据。

USES System.JSON

1）数据集转换为JSON字符串：

function TForm1.DataSetToJson(ADataset: TDataSet): string;

// [{"CityId":"18","CityName":"西安"},{"CityId":"53","CityName":"广州"}]

var

LRecord: string;

LField: TField;

i: integer;

begin

Result := '';

if (not ADataset.Active) or (ADataset.IsEmpty) then

Exit;

Result := '[';

ADataset.DisableControls;

ADataset.First;

while not ADataset.Eof do

begin

for i := 0 to ADataset.FieldCount - 1 do

begin

LField := ADataset.Fields[i];

if LRecord = '' then

LRecord := '{"' + LField.FieldName + '":"' + LField.Text + '"'

else

LRecord := LRecord + ',"' + LField.FieldName + '":"' + LField.Text + '"';

if i = ADataset.FieldCount - 1 then

begin

LRecord := LRecord + '}';

if Result = '[' then

Result := Result + LRecord

else

Result := Result + ',' + LRecord;

LRecord := '';

end;

end;

ADataset.Next;

end;

ADataset.EnableControls;

Result := Result + ']';

end;

2）JSON字符串转换为数据集：

procedure TForm1.JsonToDataSet(AJson: string; ADataset: TDataSet);

var

jDataSet: TJSONArray;

jRecord: TJSONObject;

i, j: Integer;

begin

if (AJson = '') or (ADataset = nil) or (not ADataset.Active) then

Exit;

jDataSet := TJSONObject.Create.ParseJSONValue(AJson, True) as TJSONArray;

while not ADataset.Eof do

ADataset.Delete;

for i := 0 to jDataSet.Size - 1 do

begin

ADataset.Append;

jRecord := jDataSet.Get(i) as TJSONObject;

for j := 0 to ADataset.FieldCount - 1 do

ADataset.Fields[j].Text := jRecord.GetValue(ADataset.Fields[j].FieldName).ToString;

ADataset.Post;

end;

end;