json传输对象

The data types allowed to be transfered in DataSnap 2009 is limited to the dbExpress data types, but in DataSnap 2010 part of Delphi 2010 you are allowed to transfer any kind of object.

 

Let’s define the object we would like to transfer, class TCustomer

unit Customer;

interface

uses

   DBXJSON, DBXJSONReflect, SysUtils;

type

   TMaritalStatus = (msMarried, msEngaged, msEligible);

TCustomer = class

    private

       FName: string;

       FAge: integer;

       FMaritalStatus: TMaritalStatus;

    public

        property Name: string read FName write FName;

        property Age: integer read FAge write FAge;

        property MaritalStatus: TMaritalStatus read FMaritalStatus write FMaritalStatus;

        function toString : string;override;

  end;

 

Only objects that descend from TJSONObject are able to be transferred between client and server without any transformation in DataSnap 2010. If your object does not descend from TJSONObject, then you have to use the TJSONMarshal and TJSONUnMarshal classes to convert those objects. The example below shows how to make this conversion.

function CustomerToJSON(customer: TCustomer): TJSONValue;

  var

    m: TJSONMarshal;

  begin

    if Assigned(customer) then

    begin

      m := TJSONMarshal.Create(TJSONConverter.Create);

      try

        exit(m.Marshal(customer))

      finally

        m.Free;

      end;

    end

    else

      exit(TJSONNull.Create);

  end;

 

function JSONToCustomer(json: TJSONValue): TCustomer;

  var

     unm: TJSONUnMarshal;

  begin

    if json is TJSONNull then

      exit(nil);

    unm := TJSONUnMarshal.Create;

    try

      exit(unm.Unmarshal(json) as TCustomer)

    finally

      unm.Free;

    end;

  end;

 

// protected

function TServerMethods.GetCustomer: TCustomer;

begin

  Result := TCustomer.Create;

  Result.Name := 'Pedro';

  Result.Age := 30;

  Result.MaritalStatus := msEligible;

end;

// public

function TServerMethods.GetJSONCustomer(): TJSONValue;

var

  myCustomer: TCustomer;

begin

  myCustomer := GetCustomer;

  Result := CustomerToJSON(myCustomer);

  myCustomer.Free;

end;

 

var

  proxy: TServerMethodsClient;

  myJSONCustomer: TCustomer;

begin

  try

    proxy := TServerMethodsClient.Create(SQLConnection1.DBXConnection);

    myJSONCustomer := JSONToCustomer(proxy.myJSONCustomer);

    Button1.Caption := myJSONCustomer.ToString;

    myJSONCustomer.Free;

  finally

    SQLConnection1.CloneConnection;

    proxy.Free;

  end;

end;