Generating valid identifiers
gandalf at shopzeus.com
Thu Jul 26 14:26:16 CEST 2012
I have a program that creates various database objects in PostgreSQL.
There is a DOM, and for each element in the DOM, a database object is
created (schema, table, field, index and tablespace).
I do not want this program to generate very long identifiers. It would
increase SQL parsing time, and don't look good. Let's just say that the
limit should be 32 characters. But I also want to recognize the
identifiers when I look at their modified/truncated names.
So I have come up with this solution:
- I have restricted original identifiers not to contain the dollar sign.
They can only contain [A-Z] or [a-z] or [0-9] and the underscore. Here
is a valid example:
- I'm trying to use a hash function to reduce the length of the
identifier when it is too long:
# ... more code here
def makename(cls, basename):
h = hashlib.sha256()
tail = base64.b64encode(h.digest(),"_$")[:10]
Here is the result:
So, if the identifier is too long, then I use a modified version, that
should be unique, and similar to the original name. Let's suppose that
nobody wants to crack this modified hash on purpose.
And now, the questions:
* Would it be a problem to use CRC32 instead of SHA? (Since security is
not a problem, and CRC32 is faster.)
* I'm truncating the digest value to 10 characters. Is it safe enough?
I don't want to use more than 10 characters, because then it wouldn't be
possible to recognize the original name.
* Can somebody think of a better algorithm, that would give a bigger
chance of recognizing the original identifier from the modified one?
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