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Description:

mariadbdyncol 3.6.1

Unmaintained (2022-12-07)
I stopped maintaining this package as it has never been popular.
Since MariaDB added JSON support, it’s better to use that for portability, rather than the custom dynamic columns format.
If you’d like to take over maintenance of this package please email me.

Pack/unpack Python dicts into/out of MariaDB’s Dynamic Columns format.
A quick example:
>>> mariadb_dyncol.pack({"key": "value"})
b'\x04\x01\x00\x03\x00\x00\x00\x03\x00key!value'
>>> mariadb_dyncol.unpack(mariadb_dyncol.pack({"key": "value"}))
{'key': 'value'}

Installation
Use pip:
python -m pip install mariadb-dyncol
Python 3.7 to 3.11 supported.

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Features

Sensible type mapping from Python to SQL
Tested against examples from MariaDB, including property/fuzz testing with
hypothesis (which is
amazing and found many bugs)

Why?
The normal way for adding data into dynamic columns fields is with the
COLUMN_CREATE function, and its relatives. This allows you to do things
like:
INSERT INTO mytable (attrs) VALUES (COLUMN_CREATE('key', 'value'))
Unfortunately the Django ORM is restricted and cannot use database functions
like this in every instance, at least not until Django 1.9. It was this
limitation I hit whilst implementing a dynamic columns field for my project
django-mysql that spurred the
creation of this library.
By pre-packing the dynamic columns, the above query can just insert the blob
of data directly:
INSERT INTO mytable (attrs) VALUES (X'0401000300000003006B65792176616C7565')
Asides from being more easily implemented with the Django ORM, this approach
of packing/unpacking dynamic columns in Python also has some advantages:

All data types are properly preserved in Python. The only way MariaDB
provides of pulling back all values for a dynamic columns field is to call
COLUMN_JSON, but JSON only supports strings and integers. Also
COLUMN_JSON has a depth limit of 10, but the format has no actual limit.
The CPU overhead of packing/unpacking the dynamic columns is moved from you
database server to your (presumably more scalable) clients.

API
All functions and names are accessible as attributes of the mariadb_dyncol
module, which you can import with import mariadb_dyncol.

pack(mapping)
Packs the given mapping (a dict) into the MariaDB Dynamic Columns
format for named columns and returns it as a byte string (Python 3’s bytes,
Python 2’s str). This is suitable for then inserting into a table as part
of a normal query.
The dict's keys must all be unicode strings, and the values must all be
one of the supported data types:

int between -(2 ** 32) + 1 and (2 ** 64) - 1 (Python 2: long
is supported too)
str up to 4GB encoded in UTF-8 (Python 2: unicode)
float - anything except NaN or +/- inf
datetime.datetime - full range supported
datetime.date - full range supported
datetime.time - full range supported
Any dict that is valid by these rules, allowing nested keys. There is no
nesting limit except from for MariaDB’s COLUMN_JSON function which
restricts the depth to 10

Note that this does not support the DECIMAL type that MariaDB does (and
would naturally map to Python’s Decimal) - it is a little more fiddly to
pack/unpack, though certainly possible, and pull requests are welcomed. If you
try and pack a Decimal, a DynColNotSupported exception will be raised.
There are other restrictions on the UTF-8 encoded column names as documented in
MariaDB:

The maximum length of a column name is 16383 bytes
The maximum length of all column names (at one level in nested hierarchies)
is 65535 bytes

All other unsupported types will raise a DynColTypeError. Out of range
values will raise a DynColValueError.
Examples:
>>> mariadb_dyncol.pack({"a": 1})
b'\x04\x01\x00\x01\x00\x00\x00\x00\x00a\x02'
>>> mariadb_dyncol.pack({"a": "💩"})
b'\x04\x01\x00\x01\x00\x00\x00\x03\x00a!\xf0\x9f\x92\xa9'

unpack(bytestring)
Unpacks MariaDB dynamic columns data encoded byte string into a dict; the types
you can expect back are those listed above. This is suitable for fetching the
data direct from MariaDB and decoding in Python as opposed to with MariaDB’s
COLUMN_JSON function, preserving the types that JSON discards.
As noted above, DECIMAL values are not supported, and unpacking this
will raise DynColNotSupported. Also strings will only be decoded with the
MySQL charsets utf8 or utf8mb4; strings with other charsets will raise
DynColNotSupported as well.
Unsupported column formats, for example the old MariaDB numbered dynamic
columns format, or corrupt data, will raise DynColValueError.
Examples:
>>> mariadb_dyncol.unpack(b"\x04\x01\x00\x01\x00\x00\x00\x03\x00a!\xf0\x9f\x92\xa9")
{"a": "💩"}
>>> mariadb_dyncol.unpack(b"\x04\x01\x00\x01\x00\x00\x00\x00\x00a\x02")
{"a": 1}