JSon SuperObject 研究2:数据集与JSON对象互转

JSon SuperObject 研究2:数据集与JSON对象互转

JSON不能完全替代XML，但绝对是未来的大势所趋，其优点是简单、体积小、解析更快、解析占用资源更少。在delphi中，数据集是最常用数据存取方式。因此，必须建立JSON与TDataSet之间的互转关系，实现数据之间通讯与转换。值得注意的是，这只是普通的TDataset与JSON之间转换，由于CDS包含了Delta数据包，其数据格式远比普通的TDataset更复杂。下面的程序，或许你有不同的想法，如果你的想法更好更快，欢迎一起讨论。今天是2009年最后的几十分钟，重要的并不是写博客，而是想向大家说一声“新年好运，事业有成”！

数据集字段信息，是一个完整的字典信息。因此，我们在JSON必须也建立字典信息，才能创建数据集的字段信息。我们设置其JSON信息如下：

COLS:[字段列表信息]，如：

"Cols":[{"JsonType":"integer","FieldIndex":0,"FieldType":"Integer","FieldSize":0,"FieldName":"ID","Required":false},{"JsonType":"string","FieldIndex":1,"FieldType":"String","FieldSize":100,"FieldName":"Title","Required":false},{"JsonType":"variant","FieldIndex":2,"FieldType":"Blob","FieldSize":0,"FieldName":"Picture","Required":false}]

数据信息以Data做节点，也是一个数组嵌套记录信息：

"Data":[记录集信息]

废话少说，直接上代码：

unit uDBJson;

interface

uses

SysUtils,Classes,Variants,DB,DBClient,SuperObject;

type

TTableJSon = class

private

const cstFieldType = 'FieldType';

const cstFieldName = 'FieldName';

const cstFieldSize = 'FieldSize';

const cstJsonType = 'JsonType';

const cstRequired = 'Required';

const cstFieldIndex = 'FieldIndex';

const cstCols= 'Cols';

const cstData= 'Data';

public

class function JSonFromDataSet(DataSet:TDataSet):string;

class function CreateFieldByJson(Fields:TFieldDefs;ColsJson:ISuperObject):Boolean;

class function ImportDataFromJSon(DataSet:TDataSet;DataJson:ISuperObject):Integer;

class function CDSFromJSon(CDS:TClientDataSet;Json:ISuperObject):Boolean;

class function GetValue(Json:ISuperObject;const Name:string):Variant;

class function CreateJsonValue(Json:ISuperObject;const Name:string;const Value:Variant):Boolean;

class function CreateJsonValueByField(Json:ISuperObject;Field:TField):Boolean;

class function GetValue2Field(Field:TField;JsonValue:ISuperObject):Variant;

end;

implementation

uses TypInfo,encddecd;

{ TTableJSon }

class function TTableJSon.CDSFromJSon(CDS: TClientDataSet;

Json: ISuperObject): Boolean;

var

ColsJson:ISuperObject;

begin

Result := False;

if Json = nil then

Exit;

CDS.Close;

CDS.Data := Null;

//创建字段

ColsJson := Json.O[cstCols];

CreateFieldByJson(CDS.FieldDefs,ColsJson);

if CDS.FieldDefs.Count >0 then

CDS.CreateDataSet;

ImportDataFromJSon(CDS,Json.O[cstData]);

Result := True;

end;

class function TTableJSon.CreateFieldByJson(Fields: TFieldDefs;

ColsJson: ISuperObject): Boolean;

var

SubJson:ISuperObject;

ft:TFieldType;

begin

Result := False;

Fields.DataSet.Close;

Fields.Clear;

for SubJson in ColsJson do

begin

ft := TFieldType(GetEnumValue(TypeInfo(TFieldType),'ft'+SubJson.S[cstFieldType]));

if ft= ftAutoInc then //自增字段不能录入，必须更改

ft := ftInteger;

Fields.Add(SubJson.S[cstFieldName],ft,SubJson.I[cstFieldSize],SubJson.B[cstRequired]);

end;

Result := True;

end;

class function TTableJSon.CreateJsonValue(Json: ISuperObject;

const Name: string; const Value: Variant): Boolean;

begin

Result := False;

Json.O[Name] := SO(Value);

Result := True;

end;

class function TTableJSon.CreateJsonValueByField(Json: ISuperObject;

Field: TField): Boolean;

begin

Result := False;

if Field Is TDateTimeField then

Json.O[Field.FieldName] := SO(Field.AsDateTime)

else if Field is TBlobField then

Json.S[Field.FieldName] := EncodeString(Field.AsString)

else

Json.O[Field.FieldName] := SO(Field.Value);

Result := True;

end;

class function TTableJSon.GetValue(

Json: ISuperObject;const Name: string): Variant;

begin

case Json.DataType of

stNull: Result := Null;

stBoolean: Result := Json.B[Name];

stDouble: Result := Json.D[Name];

stCurrency: Result := Json.C[Name];

stInt: Result := Json.I[Name];

stString: Result := Json.S[Name];

end;

end;

class function TTableJSon.GetValue2Field(Field: TField; JsonValue:ISuperObject): Variant;

begin

if JsonValue.DataType = stNull then

Result := Null

else if Field is TDateTimeField then

Result := JavaToDelphiDateTime(JsonValue.AsInteger)

else if (Field is TIntegerField) or (Field is TLargeintField) then

Result := JsonValue.AsInteger

else if Field is TNumericField then

Result := JsonValue.AsDouble

else if Field is TBooleanField then

Result := JsonValue.AsBoolean

else if Field is TStringField then

Result := JsonValue.AsString

else if Field is TBlobField then

Result := DecodeString(JsonValue.AsString)

end;

class function TTableJSon.ImportDataFromJSon(DataSet: TDataSet;

DataJson: ISuperObject): Integer;

var

SubJson:ISuperObject;

i:Integer;

iter: TSuperObjectIter;

begin

if not DataSet.Active then

DataSet.Open;

DataSet.DisableControls;

try

for SubJson in DataJson do

begin

DataSet.Append;

if ObjectFindFirst(SubJson,iter) then

begin

repeat

if DataSet.FindField(iter.Ite.Current.Name)<>nil then

DataSet.FindField(iter.Ite.Current.Name).Value :=

GetValue2Field(

DataSet.FindField(iter.Ite.Current.Name),

iter.Ite.Current.Value);

until not ObjectFindNext(iter) ;

end;

DataSet.Post;

end;

finally

DataSet.EnableControls;

end;

end;

class function TTableJSon.JSonFromDataSet(DataSet:TDataSet):string;

procedure GetFieldTypeInfo(Field:TField;var Fieldtyp,JsonTyp:string);

begin

Fieldtyp := GetEnumName(TypeInfo(tfieldtype),ord(Field.DataType));

Delete(Fieldtyp,1,2);

if Field is TStringField then

JsonTyp := 'string'

else if Field is TDateTimeField then

JsonTyp := 'integer'

else if (Field is TIntegerField) or (Field is TLargeintField) then

JsonTyp := 'integer'

else if Field is TCurrencyField then

JsonTyp := 'currency'

else if Field is TNumericField then

JsonTyp := 'double'

else if Field is TBooleanField then

JsonTyp := 'boolean'

else

JsonTyp := 'variant';

end;

var

sj,aj,sj2:ISuperObject;

i:Integer;

Fieldtyp,JsonTyp:string;

List:TStringList;

begin

sj := SO();

//创建列

aj := SA([]);

List := TStringList.Create;

try

List.Sorted := True;

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

begin

sj2 := SO();

GetFieldTypeInfo(DataSet.Fields[i],Fieldtyp,JsonTyp);

sj2.S[cstFieldName] := DataSet.Fields[i].FieldName;

sj2.S[cstFieldType] := Fieldtyp;

sj2.S[cstJsonType] := JsonTyp;

sj2.I[cstFieldSize] := DataSet.Fields[i].Size;

sj2.B[cstRequired] := DataSet.Fields[i].Required;

sj2.I[cstFieldIndex] := DataSet.Fields[i].Index;

aj.AsArray.Add(sj2);

List.Add(DataSet.Fields[i].FieldName+'='+JsonTyp);

end;

sj.O['Cols'] := aj;

//创建数据集的数据

DataSet.DisableControls;

DataSet.First;

aj := SA([]);

while not DataSet.Eof do

begin

sj2 := SO();

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

begin

//sj2.S[IntToStr(DataSet.Fields[i].Index)] := VarToStrDef(DataSet.Fields[i].Value,'');

if VarIsNull(DataSet.Fields[i].Value) then

sj2.O[DataSet.Fields[i].FieldName] := SO(Null)

else

begin

CreateJsonValueByField(sj2,DataSet.Fields[i]);

end;

end;

aj.AsArray.Add(sj2);

DataSet.Next;

end;

sj.O['Data'] := aj;

Result := sj.AsString;

finally

List.Free;

DataSet.EnableControls;

end;

end;

end.

调用示例：

//数据集转JSON对象或JSON文本

var

json:TTableJSon;

s:string;

begin

S := json.JSonFromDataSet(ADODataSet1);

//在用TStringStream读入字符串S，存成文本，看看其格式.

end;

//JSON对象或文本，装载到数据集
var

json:ISuperObject;

begin

json := TSuperObject.ParseFile('json.txt',False);

TTableJSon.CDSFromJSon(cdsJSON,json);

end;