NAME
sqlite3_blob_open —
Open A BLOB For
Incremental I/O
SYNOPSIS
int
sqlite3_blob_open(
sqlite3*,
const char *zDb,
const char
*zTable,
const char *zColumn,
sqlite3_int64 iRow,
int flags,
sqlite3_blob **ppBlob );
DESCRIPTION
This interfaces opens a handle to the BLOB located in row iRow, column zColumn,
table zTable in database zDb; in other words, the same BLOB that would be
selected by:
SELECT zColumn FROM zDb.zTable WHERE rowid = iRow;
Parameter zDb is not the filename that contains the database, but rather the
symbolic name of the database. For attached databases, this is the name that
appears after the AS keyword in the ATTACH statement. For the main database
file, the database name is "main". For TEMP tables, the database
name is "temp".
If the flags parameter is non-zero, then the BLOB is opened for read and write
access. If the flags parameter is zero, the BLOB is opened for read-only
access.
On success, SQLITE_OK is returned and the new BLOB handle is stored in *ppBlob.
Otherwise an error code is returned and, unless the error code is
SQLITE_MISUSE, *ppBlob is set to NULL. This means that, provided the API is
not misused, it is always safe to call sqlite3_blob_close() on *ppBlob after
this function it returns.
This function fails with SQLITE_ERROR if any of the following are true:
- Database zDb does not exist ,
- Table zTable does not exist within database zDb ,
- Table zTable is a WITHOUT ROWID table ,
- Column zColumn does not exist ,
- Row iRow is not present in the table ,
- The specified column of row iRow contains a value that
is not a TEXT or BLOB value ,
- Column zColumn is part of an index, PRIMARY KEY or
UNIQUE constraint and the blob is being opened for read/write access
,
-
Foreign key constraints are enabled, column zColumn is part of a child key
definition and the blob is being opened for read/write access .
Unless it returns SQLITE_MISUSE, this function sets the database connection
error code and message accessible via sqlite3_errcode() and sqlite3_errmsg()
and related functions.
A BLOB referenced by sqlite3_blob_open() may be read using the
sqlite3_blob_read() interface and modified by using sqlite3_blob_write(). The
BLOB handle can be moved to a different row of the same table using the
sqlite3_blob_reopen() interface. However, the column, table, or database of a
BLOB handle cannot be changed after the BLOB handle is opened.
If the row that a BLOB handle points to is modified by an UPDATE, DELETE, or by
ON CONFLICT side-effects then the BLOB handle is marked as
"expired". This is true if any column of the row is changed, even a
column other than the one the BLOB handle is open on. Calls to
sqlite3_blob_read() and sqlite3_blob_write() for an expired BLOB handle fail
with a return code of SQLITE_ABORT. Changes written into a BLOB prior to the
BLOB expiring are not rolled back by the expiration of the BLOB. Such changes
will eventually commit if the transaction continues to completion.
Use the sqlite3_blob_bytes() interface to determine the size of the opened blob.
The size of a blob may not be changed by this interface. Use the UPDATE SQL
command to change the size of a blob.
The sqlite3_bind_zeroblob() and sqlite3_result_zeroblob() interfaces and the
built-in zeroblob SQL function may be used to create a zero-filled blob to
read or write using the incremental-blob interface.
To avoid a resource leak, every open BLOB handle should eventually be released
by a call to sqlite3_blob_close().
SEE ALSO
sqlite3_blob(3),
sqlite3(3),
sqlite3_bind_blob(3),
sqlite3_blob_bytes(3),
sqlite3_blob_close(3),
sqlite3_blob_read(3),
sqlite3_blob_reopen(3),
sqlite3_blob_write(3),
sqlite3_errcode(3),
sqlite3_result_blob(3),
SQLITE_OK(3)