How to handle the null value

[Ruslan Zasukhin]

On 6/22/06 11:22 PM, "Pierre Rossel" <prossel2 at myrealbox.com> wrote:

Hi Pierre, 

> I wonder where the <Null> value is documented in Director Help and how to
> handle it.
> 
> Here is an example:
> 
> I'm creating a record using this code:
> 
> Using V4MD 1.11 on XP and OS X. I use the following code to add a record.
> The #mediaData field value is not provided. It is a #Text field (not
> nullable, indexed by words, ASCII, segment 128).
> 
>   curMediaItems = db.Query("SELECT RecID, * FROM MediaItem WHERE RecID=0",
> [#LockType: #ReadWrite, #Direction: #Random])
>   bRet = curMediaItems.AddRecord([#MediaFolderPtr: iMediaFolderId, #name:
> sName, #mediaType: 1])
> 
> Later, this code is used to load the data. The result of the put commands
> are merged under the commands.
> 
>   curItem = db.Query("SELECT * FROM MediaItem WHERE RecID=" &
> p_iMediaItemId)
>   p_lstData = curItem.GetRecordAsPropList()
> 
>   put p_lstData[#mediaData]
>   -- <Null>
> 
>   put p_lstData[#mediaData] = void
>   -- 1
> 
>   put voidP(p_lstData[#mediaData])
>   -- 0
> 
> The <Null> value is something I have never seen documented. Is it the same
> as void ? Seems not since the voidP() call return false. Usually the test
> value = void should be avoided and the voidP() function used instead. In
> this situation, it is just the opposite.
> 
> I am a bit confused.

Well, I believe that V4MD returns VOID type when some field value
has NULL of SQL

Director has the following types:

enum
{
    kMoaMmValueType_Void,
    kMoaMmValueType_Integer,
    kMoaMmValueType_Symbol,
    kMoaMmValueType_String,
    kMoaMmValueType_Object,
    kMoaMmValueType_Picture,
    kMoaMmValueType_Float,
    kMoaMmValueType_List,
    kMoaMmValueType_Point,
    kMoaMmValueType_Rect,
    kMoaMmValueType_PropList,
    kMoaMmValueType_Member,
    kMoaMmValueType_CastLib,
    kMoaMmValueType_Script,
    kMoaMmValueType_Instance,
    kMoaMmValueType_Xtra,
    kMoaMmValueType_Sprite,
    kMoaMmValueType_SoundSprite,
    kMoaMmValueType_Color,
    kMoaMmValueType_Date,
    kMoaMmValueType_Media,
    kMoaMmValueType_Other,
    kMoaMmValueType_3dVector,
    kMoaMmValueType_3dTransform,
};


And we use VOID to get/set the NULL value.

Also note, exist VField_IsNull() method, which allow test field
value on NULL.


-- 
Best regards,

Ruslan Zasukhin
VP Engineering and New Technology
Paradigma Software, Inc

Valentina - Joining Worlds of Information
http://www.paradigmasoft.com

[I feel the need: the need for speed]