How to store IInterface variable in ORM

BenTen · 2021-09-16 18:51:33

Hi, ab
Help me please
How correctly to convert IInterface type to store in ORM database?

unit Unit1;

interface
type
  ISomeInterface = interface
    ['{0A799B7B-3BBB-4159-B59F-BD3B03AA654F}']
    function GetProvider: RawUTF8;
  end;

  TSQLProviders = class(TSQLRecord)
  private
    FIntf: ISomeInterface;                                                 {What type of interface variable?}
  published
    property Intf: ISomeInterface read FIntf write FIntf;
  end;

  TSomeObject = class
  protected
    FIntf: ISomeInterface;
    FRest: TSQLRest;
  public
    constructor Create;
  end;

implementation

constructor TSomeObject.Create;
var
  Rec: TSQLProviders;
  Provider: RawUTF8;
begin
   FRest := TSQLRestServerFullMemory.CreateWithOwnModel([TSQLProviders]);
   FRest.CreateMissingTables;
   TSQLProviders.AutoFree(Rec);

   Intf := TSomeProvider.Create;
   Rec.Intf :=  Intf;                               {how to convert interface variable to store in database?}
   FRest.Add(Rec,'',True);

   Provider := Rec.Intf.GetProvider;        {how to call the interface method from database?}

end;


end.

ab · 2021-09-16 18:55:36

It is not supported, nor possible.

How could such an interface be unserialized?
You are messing things up.

BenTen · 2021-09-16 20:27:00

Did the IInterface type variable is not a pointer?

BenTen · 2021-09-16 21:08:32

Thanks
That's how it works

...
 TSQLProviders = class(TSQLRecord)
  private
    FIntf: UIntPtr;                                                 {What type of interface variable?}
  published
    property Intf: UIntPtr read FIntf write FIntf;
  end;
....
    Intf := TSomeProvider.Create;
   Rec.Intf :=  UIntPtr(Intf);                                            {how to convert interface variable to store in database?}
   FRest.Add(Rec,True);
....
   Provider := ISomeInterface(Rec.Intf).GetProvider;        {how to call the interface method from database?}

ab · 2021-09-17 07:18:55

You can't persist an interface pointer.
It is depending on the execution context.
If you restart the application for instance, the pointer value will be incorrect for sure.
So I don't see the point of saving a pointer into a database.

We can save classes, because we don't save their pointer, but their attributes/fields values.

What you could do is save an integer ID which may be able to create an interface instance from the database.
But this is something else.

BenTen · 2021-09-17 15:00:12

Thanks, ab

ab wrote:

You can't persist an interface pointer.
It is depending on the execution context.

This is just what I need.
I need to save an interface pointer within the execution context into the FullInMemory database

ab · 2021-09-18 13:00:08

You could use the PtrUInt() type cast but be aware that it won't increase the reference count: it returns a "weak" interface instance.

BenTen · 2021-09-21 20:23:16

Thanks, ab.
I understood it.
I have to use InterfaceArrayAdd and InterfaceArrayDelete each time I add or delete the interface into the database

mORMot Open Source

#1 2021-09-16 18:51:33

How to store IInterface variable in ORM

#2 2021-09-16 18:55:36

Re: How to store IInterface variable in ORM

#3 2021-09-16 20:27:00

Re: How to store IInterface variable in ORM

#4 2021-09-16 21:08:32

Re: How to store IInterface variable in ORM

#5 2021-09-17 07:18:55

Re: How to store IInterface variable in ORM

#6 2021-09-17 15:00:12

Re: How to store IInterface variable in ORM

#7 2021-09-18 13:00:08

Re: How to store IInterface variable in ORM

#8 2021-09-21 20:23:16

Re: How to store IInterface variable in ORM

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