Blob Class

The Blob class defines the common properties of objects of type BLOB. A BLOB is a large binary object stored as a column value in a row of a database table. A Blob object contains a logical pointer to a BLOB, not the BLOB itself.

Methods of the Blob class enable you to perform specific tasks related to Blob objects.

Methods of the ResultSet and Statement classes, such as getBlob() and setBlob(), enable you to access an SQL BLOB value.

The only methods valid on a NULL Blob object are setName(), isNull(), and operator=().

An uninitialized Blob object can be initialized by:

• The setEmpty() method. The BLOB can then be modified by inserting this BLOB into the table and then retrieving it using SELECT ... FOR UPDATE. The write() method will modify the BLOB; however, the modified data will be flushed to the table only when the transaction is committed. Note that an update is not required.

• Assigning an initialized Blob object to it.

Blob()

Blob class constructor.

Blob();

Blob(
   const Connection *connectionp);

Blob(
   const Blob &srcBlob);

connectionp

srcBlob

append()

Appends a BLOB to the end of the current BLOB.

Syntax

void append(
   const Blob &srcBlob);

srcBlob

close()

Closes a BLOB.

Syntax

void close();

closeStream()

Closes the Stream object obtained from the BLOB.

Syntax

void closeStream(
   Stream *stream);

stream

copy()

Copies a part or all of a BFILE or BLOB into the current BLOB.

void copy(
   const Bfile &srcBfile,
   unsigned int numBytes,
   unsigned int dstOffset = 1,
   unsigned int srcOffset = 1);

void copy(
   const Blob &srcBlob,
   unsigned int numBytes,
   unsigned int dstOffset = 1,
   unsigned int srcOffset = 1);

srcBfile

srcBlob

numBytes

dstOffset

srcOffset

getChunkSize()

Returns the chunk size of the BLOB. When creating a table that contains a BLOB, the user can specify the chunking factor, which can be a multiple of Oracle blocks. This corresponds to the chunk size used by the LOB data layer when accessing or modifying the BLOB.

Syntax

unsigned int getChunkSize() const;

getStream()

Returns a Stream object from the BLOB. If a stream is already open, it is disallowed to open another stream on Blob object, so the user must always close the stream before performing any Blob object operations.

Syntax

Stream* getStream(
   unsigned int offset = 1,
   unsigned int amount = 0);

offset

amount

isInitialized()

Tests whether the Blob object is initialized. If the Blob object is initialized, then TRUE is returned; otherwise, FALSE is returned.

Syntax

bool isInitialized() const;

isNull()

Tests whether the Blob object is atomically NULL. If the Blob object is atomically NULL, then TRUE is returned; otherwise, FALSE is returned.

Syntax

bool isNull() const;

isOpen()

Tests whether the BLOB is open. If the BLOB is open, then TRUE is returned; otherwise, FALSE is returned.

Syntax

bool isOpen() const;

length()

Returns the number of bytes in the BLOB.

Syntax

unsigned int length() const;

open()

Opens the BLOB in read/write or read-only mode.

Syntax

void open(
   LobOpenMode mode = OCCI_LOB_READWRITE);

mode

operator=()

Assigns a BLOB to the current BLOB. The source BLOB gets copied to the destination BLOB only when the destination BLOB gets stored in the table.

Syntax

Blob& operator=(
   const Blob &srcBlob);

srcBlob

operator==()

Compares two Blob objects for equality. Two Blob objects are equal if they both refer to the same BLOB. Two NULL Blob objects are not considered equal. If the Blob objects are equal, then TRUE is returned; otherwise, FALSE is returned.

Syntax

bool operator==(
   const Blob &srcBlob) const;

srcBlob

operator!= ()

Compares two Blob objects for inequality. Two Blob objects are equal if they both refer to the same BLOB. Two NULL Blob objects are not considered equal. If the Blob objects are not equal, then TRUE is returned; otherwise, FALSE is returned.

Syntax

bool operator!=(
   const Blob &srcBlob) const;

srcBlob

read()

Reads a part or all of the BLOB into a buffer. The actual number of bytes read is returned.

Syntax

unsigned int read(
   unsigned int amt,
   unsigned char *buffer,
   unsigned int bufsize,
   unsigned int offset = 1) const;

amt

buffer

buffsize

offset

setEmpty()

Sets the Blob object to empty.

void setEmpty();

void setEmpty(
   const Connection* connectionp);

connectionp

setNull()

Sets the Blob object to atomically NULL.

Syntax

void setNull();

trim()

Truncates the BLOB to the new length specified.

Syntax

void trim(
   unsigned int newlen);

newlen

write()

Writes data from a buffer into a BLOB. This method implicitly opens the BLOB, copies the buffer into the BLOB, and implicitly closes the BLOB. If the BLOB is already open, use writeChunk() instead. The actual number of bytes written is returned.

Syntax

unsigned int write(
   unsigned int amt,
   unsigned char *buffer,
   unsigned int bufsize,
   unsigned int offset = 1);

amt

buffer

buffsize

offset

writeChunk()

Writes data from a buffer into a previously opened BLOB. The actual number of bytes written is returned.

Syntax

unsigned int writeChunk(
   unsigned int amount,
   unsigned char *buffer,
   unsigned int bufsize,
   unsigned int offset = 1);

amt

buffer

buffsize

offset