Question

I’m using the MySQLdb package for interacting with MySQL. I’m having trouble getting the proper type conversions.

I am using a 16-byte binary uuid as a primary key for the table and have a mediumblob holding zlib compressed json information.

I’m using the following schema:

CREATE TABLE repositories (
    added_id int auto_increment not null,
    id binary(16) not null,
    data mediumblob not null,
    create_date int not null,
    update_date int not null,
    PRIMARY KEY (added_id),
    UNIQUE(id)
) DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci ENGINE=InnoDB;

Then I create a new row in the table using the following code:

data = zlib.compress(json.dumps({'hello':'how are you :D'})
row_id = uuid.uuid(4).hex
added_id = cursor.execute('
    INSERT INTO repositories (id, data, create_date, update_date) 
    VALUES (%s, %s, %s, %s)',
    binascii.a2b_hex(row_id), 
    data, 
    time.time(), 
    time.time()
)

Then to retrieve data I use a similar query:

query = cursor.execute('SELECT added_id, id, data, create_date, update_date ' \
    'FROM repositories WHERE id = %s',
    binascii.a2b_hex(row_id)
)

Then the query returns an empty result.

Any help would be appreciated. Also, as an aside, is it better to store unix epoch dates as integers or TIMESTAMP?

NOTE: I am not having problems inserting the data, just trying to retrieve it from the database. The row exists when I check via mysqlclient.

Thanks Alot!@

Answer 1

One tip: you should be able to call uuid.uuid4().bytes to get the raw
bytes. As for timestamps, if you want to perform time/date manipulation
in SQL it’s often easier to deal with real TIMESTAMP types.

I created a test table to try to reproduce what you’re seeing:

CREATE TABLE xyz (
    added_id INT AUTO_INCREMENT NOT NULL,
    id BINARY(16) NOT NULL,
    PRIMARY KEY (added_id),
    UNIQUE (id)
) DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci ENGINE=InnoDB;

My script is able to insert and query for the rows using the binary field as a
key without problem. Perhaps you are incorrectly fetching / iterating over the
results returned by the cursor?

import binascii
import MySQLdb
import uuid

conn = MySQLdb.connect(host='localhost')

key = uuid.uuid4()
print 'inserting', repr(key.bytes)
r = conn.cursor()
r.execute('INSERT INTO xyz (id) VALUES (%s)', key.bytes)
conn.commit()

print 'selecting', repr(key.bytes)
r.execute('SELECT added_id, id FROM xyz WHERE id = %s', key.bytes)
for row in r.fetchall():
    print row[0], binascii.b2a_hex(row[1])

Output:

% python qu.py    
inserting '\x96\xc5\xa4\xc3Z+L\xf0\x86\x1e\x05\xebt\xf7\\\xd5'
selecting '\x96\xc5\xa4\xc3Z+L\xf0\x86\x1e\x05\xebt\xf7\\\xd5'
1 96c5a4c35a2b4cf0861e05eb74f75cd5
% python qu.py
inserting '\xac\xc9,jn\xb2O@\xbb\xa27h\xcd<B\xda'
selecting '\xac\xc9,jn\xb2O@\xbb\xa27h\xcd<B\xda'
2 acc92c6a6eb24f40bba23768cd3c42da