Blob Cl a ss

Blob Cl ass

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.

See Also:

In-depth discussion of LOBs in the introductory chapter of Oracle Database Application Developer's Guide - Large Objects,

Table 10-6 Summary of Blob Methods

Method	Summary
Blob()	`Blob` class constructor.
append()	Append a specified `BLOB` to the end of the current BLOB.
close()	Close a previously opened BLOB.
closeStream()	Close the `Stream` object obtained from the BLOB.
copy()	Copy a specified portion of a `BFILE` or BLOB into the current BLOB.
getChunkSize()	Return the chunk size of the BLOB.
getStream()	Return data from the BLOB as a `Stream` object.
isInitialized()	Test whether the `Blob` object is initialized
isNull()	Test whether the `Blob` object is atomically `NULL`.
isOpen()	Test whether the BLOB is open
length()	Return the number of bytes in the BLOB.
open()	Open the BLOB `with read or` read/write access.
operator=()	Assign a BLOB locator to the `Blob` object.
operator==()	Test whether two `Blob` objects are equal.
operator!=()	Test whether two `Blob` objects are not equal.
operator==()	Read a portion of the BLOB into a buffer.
setEmpty()	Set the `Blob` object to empty.
setEmpty()	Set the `Blob` object to empty and initializes the connection pointer to the passed parameter.
setName()	Set the `Blob` object to atomically `NULL`.
trim()	Truncate the BLOB to a specified length.
write()	Write a buffer into an unopened BLOB.
writeChunk()	Write a buffer into an open BLOB.

Blob()

Blob class constructor.

Syntax	Description
Blob();	Creates a `NULL` `Blob` object.
Blob( const Connection *connectionp);	Create an uninitialized `Blob` object.
Blob( const Blob &srcBlob);	Create a copy of a `Blob` object.

Parameter	Description
connectionp	The connection pointer
srcBlob	The source `Blob` object.

append()

Appends a BLOB to the end of the current BLOB.

Syntax

void append(
   const Blob &srcBlob);

Parameter	Description
srcBlob	The `BLOB` object to be appended to the current `BLOB` object.

close()

Closes a BLOB.

Syntax

void close();

closeStream()

Closes the Stream object obtained from the BLOB.

Syntax

void closeStream(
   Stream *stream);

Parameter	Description
stream	The `Stream` to be closed.

copy()

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

Syntax Description

Syntax	Description
void copy( const Bfile &srcBfile, unsigned int numBytes, unsigned int dstOffset = 1, unsigned int srcOffset = 1);	Copies a part of a `BFILE` into the current `BLOB`.
void copy( const Blob &srcBlob, unsigned int numBytes, unsigned int dstOffset = 1, unsigned int srcOffset = 1);	Copies a part of a `BLOB` into the current `BLOB`.

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

Copies a part of a BFILE into the current BLOB.

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

Copies a part of a BLOB into the current BLOB.

Parameter	Description
srcBfile	The `BFILE` from which the data is to be copied.
srcBlob	The `BLOB` from which the data is to be copied.
numBytes	The number of bytes to be copied from the source `BFILE` or `BLOB`. Valid values are numbers greater than 0.
dstOffset	The starting position at which to begin writing data into the current `BLOB`. Valid values are numbers greater than or equal to 1.
srcOffset	The starting position at which to begin reading data from the source `BFILE` or `BLOB`. Valid values are numbers greater than or equal to 1.

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);

Parameter	Description
offset	The starting position at which to begin reading data from the `BLOB`. If `offset` is not specified, the data is written from the beginning of the `BLOB`. Valid values are numbers greater than or equal to `1`.
amount	The total number of bytes to be read from the `BLOB`; if `amount` is `0`, the data will be read in a streamed mode from input `offset` until the end of the `BLOB`.

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);

Parameter	Description
mode	The mode the `BLOB` is to be opened in. Valid values are: `OCCI_LOB_READWRITE` `OCCI_LOB_READONLY`

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);

Parameter	Description
srcBlob	The source `BLOB` from which to copy data.

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;

Parameter	Description
srcBlob	The source `BLOB` to be compared with the current `BLOB`.

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;

Parameter	Description
srcBlob	The source `BLOB` to be compared with the current `BLOB`.

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;

Parameter	Description
amt	The number of bytes to be read. Valid values are numbers greater than or equal to `1`.
buffer	The buffer that the `BLOB` data is to be read into. Valid values are numbers greater than or equal to `amt`.
buffsize	The size of the buffer that the `BLOB` data is to be read into. Valid values are numbers greater than or equal to `amt`.
offset	The starting position at which to begin reading data from the `BLOB`. If `offset` is not specified, the data is written from the beginning of the `BLOB`.

setEmpty()

Sets the Blob object to empty.

Syntax

void setEmpty();

setEmpty()

Sets the Blob object to empty and initializes the connection pointer to the passed parameter.

Syntax

void setEmpty(
   const Connection* connectionp);

Parameter	Description
connectionp	The new connection pointer for the Blob object.

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);

Parameter	Description
newlen	The new length of the `BLOB`. Valid values are numbers less than or equal to the current length of the `BLOB`.

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);

Parameter	Description
amt	The number of bytes to be written to the `BLOB`.
buffer	The buffer containing the data to be written to the `BLOB`.
buffsize	The size of the `buffer containing the data to be written to the` `BLOB.` Valid values are numbers greater than or equal to `amt`.
offset	The starting position at which to begin writing data into the `BLOB`. If `offset` is not specified, the data is written from the beginning of the `BLOB`. Valid values are numbers greater than or equal to 1.

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);

Parameter	Description
amt	The number of bytes to be written to the `BLOB`.
buffer	The buffer containing the data to be written to the `BLOB`.
buffsize	The size of the buffer containing the data to be written to the `BLOB`. Valid values are numbers greater than or equal to `amt`.
offset	The starting position at which to begin writing data into the `BLOB`. If `offset` is not specified, the data is written from the beginning of the `BLOB`. Valid values are numbers greater than or equal to `1`.

Blob Class

Blob()

append()

close()

closeStream()

copy()

getChunkSize()

getStream()

isInitialized()

isNull()

isOpen()

length()

open()

operator=()

operator==()

operator!= ()

read()

setEmpty()

setEmpty()

setNull()

trim()

write()

writeChunk()

Blob Cl ass