Blobs

Blobs — Binary data and BLOBs handling

Synopsis




                    GdaBlobOp;
glong               gda_blob_op_get_length              (GdaBlobOp *op);
glong               gda_blob_op_read                    (GdaBlobOp *op,
                                                         GdaBlob *blob,
                                                         glong offset,
                                                         glong size);
gboolean            gda_blob_op_read_all                (GdaBlobOp *op,
                                                         GdaBlob *blob);
glong               gda_blob_op_write                   (GdaBlobOp *op,
                                                         GdaBlob *blob,
                                                         glong offset);
gboolean            gda_blob_op_write_all               (GdaBlobOp *op,
                                                         GdaBlob *blob);

Object Hierarchy


  GObject
   +----GdaBlobOp

Description

This object is a base class for individual database providers which support BLOB types. It supports operations to read and write data in a BLOB value (of type GDA_BLOB_TYPE).

Libgda offers two methods to manipulate binary values as two containers: GdaBinary and GdaBlob:

  • When reading from a data model returned by libgda binary data will often be in a GdaBlob object, and the associated GdaBlobOp object can be used to manipulate the binary object (in a database for example)

  • When the binary value is created by the user, then there is no point in using a GdaBlob as there can not be any GdaBlobOp object, so the GdaBinary container is enough.

Note that a GdaBlob value will often not contain any data (or only some part of the actual BLOB) and that it's up to the user to use the associated GdaBlobOp object to "load" the data into the container (into the actual process heap).

Details

GdaBlobOp

typedef struct _GdaBlobOp GdaBlobOp;

gda_blob_op_get_length ()

glong               gda_blob_op_get_length              (GdaBlobOp *op);

Opens an existing BLOB. The BLOB must be initialized by gda_connection_create_blob or obtained from a GValue. FIXME: gda_connection_create_blob() no longer exists.

op : an existing GdaBlobOp
Returns : the length of the blob in bytes. In case of error, -1 is returned and the provider should have added an error (a GdaConnectionEvent) to the connection.

gda_blob_op_read ()

glong               gda_blob_op_read                    (GdaBlobOp *op,
                                                         GdaBlob *blob,
                                                         glong offset,
                                                         glong size);

Reads a chunk of bytes from the BLOB into blob.

op : a GdaBlobOp
blob : a GdaBlob to read data to
offset : offset to read from the start of the blob (starts at 0)
size : maximum number of bytes to read.
Returns : the number of bytes actually read. In case of error, -1 is returned and the provider should have added an error to the connection.

gda_blob_op_read_all ()

gboolean            gda_blob_op_read_all                (GdaBlobOp *op,
                                                         GdaBlob *blob);

Reads the whole contents of the blob manipulated by op into blob

op : a GdaBlobOp
blob : a GdaBlob to read data to
Returns : TRUE if blob->data contains the whole BLOB manipulated by op

gda_blob_op_write ()

glong               gda_blob_op_write                   (GdaBlobOp *op,
                                                         GdaBlob *blob,
                                                         glong offset);

Writes a chunk of bytes from a blob to the BLOB accessible through op.

op : a GdaBlobOp
blob : a GdaBlob which contains the data to write
offset : offset to write from the start of the blob (starts at 0)
Returns : the number of bytes written. In case of error, -1 is returned and the provider should have added an error to the connection.

gda_blob_op_write_all ()

gboolean            gda_blob_op_write_all               (GdaBlobOp *op,
                                                         GdaBlob *blob);

Writes the whole contents of blob into the blob manipulated by op. If necessary the resulting blob is truncated from its previous length.

op : a GdaBlobOp
blob : a GdaBlob which contains the data to write
Returns : TRUE on success