None

None

This class has no public constructor. An instance of NdbBlob is created using the NdbOperation::getBlobHandle() method during the operation preparation phase. (See Section 2.3.20, “The NdbOperation Class”.) This object acts as a handle on a blob column.

The following table lists the public methods of this class and the purpose or use of each method:

getBlobTableName() and getBlobEventName() are static methods.

Most NdbBlob methods (nearly all of those whose return type is int) return 0 on success and -1 in the event of failure.

The public types defined by NdbBlob are shown here:

This is a callback for NdbBlob::setActiveHook(), and is invoked immediately once the prepared operation has been executed (but not committed). Any calls to getValue() or setValue() are performed first. The blob handle is active so readData() or writeData() can be used to manipulate the blob value. A user-defined argument is passed along with the NdbBlob. setActiveHook() returns a nonzero value in the event of an error.

This method initialises a list of blobs belonging to the current operation and returns the first blob in the list.

NdbBlob* blobsFirstBlob
    (
      void
    )

None.

A pointer to the desired blob.

Use the method to obtain the next in a list of blobs that was initialised using blobsFirstBlob(). See NdbBlob::blobsFirstBlob().

NdbBlob* blobsNextBlob
    (
      void
    )

None.

A pointer to the desired blob.

Closes the blob handle, releasing internal resources as it does so, prior to committing or aborting the transaction. In other words, this signals that an application has finished with reading from a given blob. This method can be called only when the blob's State is Active.

int close
    (
      bool execPendingBlobOps = true
    )

This method has a single boolean parameter execPendingBlobOps. If the value of this parameter true (the default), any pending blob operations are flushed before the blob handle is closed. If execPendingBlobOps is false, then it is assumed that the blob handle has no pending read or write operations to flush.

0 on success.

This method gets a blob event name. The blob event is created if the main event monitors the blob column. The name includes the main event name.

static int getBlobEventName
    (
      char*       name,
      Ndb*        ndb,
      const char* event,
      const char* column
    )

This method takes the four parameters listed here:

0 on success, -1 on failure.

This method gets the blob data segment table name.

This method is generally of use only for testing and debugging purposes.

static int getBlobTableName
    (
      char*       name,
      Ndb*        ndb,
      const char* table,
      const char* column
    )

This method takes the four parameters listed here:

Returns 0 on success, -1 on failure.

Use this method to get the blob column to which the NdbBlob belongs.

const Column* getColumn
    (
      void
    )

None.

A Column object.

This method gets the blob's current length in bytes.

int getLength
    (
      Uint64& length
    )

A reference to the length.

The blob's length in bytes. For a NULL blob, this method returns 0. to distinguish between a blob whose length is 0 blob and one which is NULL, use the getNull() method.

This method checks whether the blob's value is NULL.

int getNull
    (
      int& isNull
    )

A reference to an integer isNull. Following invocation, this parameter has one of the following values, interpreted as shown here:

None.

Use this method to obtain an error object. The error may be blob-specific or may be copied from a failed implicit operation. The error code is copied back to the operation unless the operation already has a nonzero error code.

const NdbError& getNdbError
    (
      void
    ) const

None.

An NdbError object.

This method can be used to find the operation with which the handle for this NdbBlob is associated.

const NdbOperation* getNdbOperation
    (
      void
    ) const

None.

A pointer to an operation.

The operation referenced by the pointer returned by this method may be represented by either an NdbOperation or NdbScanOperation object.

See Section 2.3.20, “The NdbOperation Class”, and Section 2.3.24, “The NdbScanOperation Class”, for more information.

This method gets the current read/write position in a blob.

int getPos
    (
      Uint64& pos
    )

One parameter, a reference to the position.

Returns 0 on success, or -1 on failure. (Following a successful invocation, pos will hold the current read/write position within the blob, as a number of bytes from the beginning.)

This method gets the current state of the NdbBlob object for which it is invoked. Possible states are described in NdbBlob::State.

State getState
    (
      void
    )

None.

A value of type State.

Use this method to prepare to read a blob value; the value is available following invocation. Use getNull() to check for a NULL value; use getLength() to get the actual length of the blob, and to check for truncation. getValue() sets the current read/write position to the point following the end of the data which was read.

int getValue
    (
      void*  data,
      Uint32 bytes
    )

This method takes two parameters. The first of these is a pointer to the data to be read; the second is the number of bytes to be read.

0 on success, -1 on failure.

This method is used to distinguish whether a blob operation is statement-based or event-based.

void getVersion
    (
      int& version
    )

This method takes a single parameter, an integer reference to the blob version (operation type).

One of the following three values:

getVersion() is always successful, assuming that it is invoked as a method of a valid instance of NdbBlob.

This method is used to read data from a blob.

int readData
    (
      void*     data,
      Uint32&  bytes
    )

readData() accepts a pointer to the data to be read, and a reference to the number of bytes read.

Returns 0 on success, -1 on failure. Following a successful invocation, data points to the data that was read, and bytes holds the number of bytes read.

This method defines a callback for blob handle activation. The queue of prepared operations will be executed in no-commit mode up to this point; then, the callback is invoked. For additional information, see NdbBlob::ActiveHook.

int setActiveHook
    (
      ActiveHook*  activeHook,
      void*        arg
    )

This method requires the two parameters listed here:

0 on success, -1 on failure.

This method sets the value of a blob to NULL.

int setNull
    (
      void
    )

None.

0 on success; -1 on failure.

This method sets the position within the blob at which to read or write data.

int setPos
    (
      Uint64 pos
    )

The setPos() method takes a single parameter pos (an unsigned 64-bit integer), which is the position for reading or writing data. The value of pos must be between 0 and the blob's current length.

0 on success, -1 on failure.

This method is used to prepare for inserting or updating a blob value. Any existing blob data that is longer than the new data is truncated. The data buffer must remain valid until the operation has been executed. setValue() sets the current read/write position to the point following the end of the data. You can set data to a null pointer (0) in order to create a NULL value.

int setValue
    (
      const void*  data,
      Uint32       bytes
    )

This method takes the two parameters listed here:

0 on success, -1 on failure.

An NdbBlob may assume any one of these states

Possible values are shown, along with descriptions, in the following table:

This method is used to truncate a blob to a given length.

int truncate
    (
      Uint64 length = 0
    )

truncate() takes a single parameter which specifies the new length to which the blob is to be truncated. This method has no effect if length is greater than the blob's current length (which you can check using getLength()).

0 on success, -1 on failure.

This method is used to write data to an NdbBlob. After a successful invocation, the read/write position will be at the first byte following the data that was written to the blob.

A write past the current end of the blob data extends the blob automatically.

int writeData
    (
      const void*  data,
      Uint32       bytes
    )

This method takes two parameters, a pointer to the data to be written, and the number of bytes to write.

0 on success, -1 on failure.