4D Doc Center : DOCUMENT TO BLOB

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4D v14.3

BLOB

DOCUMENT TO BLOB


DOCUMENT TO BLOB ( document ; blob {; *} )

Parameter	Type	Description
document	String	Name of the document
blob	BLOB	BLOB field or variable to receive the document
		Document contents
*	Operator	On Macintosh only: Resource fork is loaded if * is passed otherwise Data fork is loaded

Description

DOCUMENT TO BLOB loads the whole contents of document into blob. You must pass the name of an existing document that is not already open, otherwise an error will be generated. To let the user choose the document to be loaded into the BLOB, use the command Open document and the process variable document (see Example).

Note regarding Macintosh: Macintosh documents can be composed of two forks: the Data fork and the Resource fork. By default, the command DOCUMENT TO BLOB loads the Data fork of the document. To load the Resource fork of the document instead, pass the optional * parameter. On Windows, the optional * parameter is ignored. Note that the 4D environment provides the equivalent of Mac OS resource forks on Windows. For example, the data fork of a 4D database is stored in a file with the file extension .4DB; the resource fork is stored in a file with the same name and the file extension .RSR. On Windows, if you write a 4D application with the data fork and resource fork stored in BLOBs, you just need to access the file corresponding to the fork with which you want to work.

Example

You write an Information System that enables you to quickly store and retrieve documents. In a data entry form, you create a button that allows you to load a document into a BLOB field. The method for this button could be:

 $vhDocRef:=Open document("") ` Select the document of your choice

 If(OK=1) ` If a document has been chosen

    CLOSE DOCUMENT($vhDocRef) ` We don't need to keep it open

    DOCUMENT TO BLOB(Document;[YourTable]YourBLOBField) ` Load the document

    If(OK=0)

  ` Handle error

    End if

 End if

System variables and sets

OK is set to 1 if the document is correctly loaded, otherwise OK is set to 0 and an error is generated.

Error Handling

If you try to load (into a BLOB) a document that does not exist or that is already open by another process or application, the appropriate File Manager error is generated.
An I/O error can occur if the document is locked, located on a locked volume, or if there is problem in reading the document.
If there is not enough memory to load the document, an error -108 is generated.

In each case, you can trap the error using an ON ERR CALL interruption method.