How do I write a BLOB, any BLOB to sqlite? - objective-c

Question

I need to write an Obj-C object (e.g. NSString in this case) to a sqlite database and store it in a BLOB column, using Python 2.7.
To that extent I wrote this demo code that fails with the below traceback.
from sqlite3 import connect
from Foundation import NSArchiver
conn = connect(':memory:')
create = "CREATE TABLE test(data BLOB)"
conn.execute(create)
conn.commit()
blob = NSArchiver.archivedDataWithRootObject_("Hello World").bytes()
print type(blob), blob
sql = "INSERT INTO test VALUES (?)"
data = [blob]
conn.execute(sql, data)
conn.commit()
This traces back with:
$ ./sqlite3_test.py
<type 'memoryview'> <memory at 0x104a5e218>
Traceback (most recent call last):
File "./sqlite3_test.py", line 16, in <module>
conn.execute(sql, data)
sqlite3.InterfaceError: Error binding parameter 0 - probably unsupported type.
No amount of magik using sqlite3.Binary (which is defined as Binary = buffer inside the sqlite3 module) or .tobytes() (from memoryview) made that work any better.
I also tried to create a buffer() object out of the NSArchiver blob, but a naïve approach:
b = buffer(blob, 0, len(blob))
traces back with TypeError: buffer object expected - arguably NSArchiver objects are not Python strings.

Answer 1

I got a working example!
On the Objective-C call bytes() I need to call the memoryview .tobytes() which can then be serialized to buffer().
#!/usr/bin/python -tt
from sqlite3 import connect, Binary
from Foundation import NSArchiver
conn = connect(':memory:')
create = "CREATE TABLE test(data BLOB)"
conn.execute(create)
conn.commit()
str = NSString.alloc().initWithString_("Hello World")
blob = NSArchiver.archivedDataWithRootObject_(str).bytes().tobytes()
print "Original (%s): %s" % (len(blob), blob)
sql = "INSERT INTO test VALUES (?)"
data = [Binary(blob)]
conn.execute(sql, data)
conn.commit()
cursor = conn.cursor()
cursor.execute("SELECT * FROM test")
rows = cursor.fetchall()
for r in rows:
print "In database (%s): %s" % (len(r[0]), r[0])
This gives:
$ ./sqlite3_test.py
Original (84):
streamtyped???#???OC_PythonString?NSString?NSObject??i?+
Hello World?
In database (84):
streamtyped???#???OC_PythonString?NSString?NSObject??i?+
Hello World?