Question

I have firmware version strings into my table (like “4.2.2” or “4.2.16”)

How can I compare, select or sort them ?

I cannot use standard strings comparison : “4.2.2” is a seen by SQL greater than “4.2.16”

As version strings, I would like 4.2.16 to be greater than 4.2.2

I would like to consider that firmware version can have chars in them : 4.24a1, 4.25b3 … for this, usually, the subfield with chars has a fixed length.

how to proceed ?

Answer 1

Finally, I found another way to sort version strings.

I just justify the string before storing into de database in a way it is sortable.
As I am using the python Django framework, I just have created a VersionField that ‘encode’ the version string while storing and ‘decode’ it while reading, so that it is totally transparent for the application :

Here my code :

The justify function :

def vjust(str,level=5,delim='.',bitsize=6,fillchar=' '):
    """
    1.12 becomes : 1.    12
    1.1  becomes : 1.     1
    """
    nb = str.count(delim)
    if nb < level:
        str += (level-nb) * delim
    return delim.join([ v.rjust(bitsize,fillchar) for v in str.split(delim)[:level+1] ])

The django VersionField :

class VersionField(models.CharField) :

    description = 'Field to store version strings ("a.b.c.d") in a way it is sortable'

    __metaclass__ = models.SubfieldBase

    def get_prep_value(self, value):
        return vjust(value,fillchar=' ')

    def to_python(self, value):
        return re.sub('\.+$','',value.replace(' ',''))