[hibernate-dev] strategies for truncating identifiers

[Brett Meyer]

I've been working a bit on HHH-1904 [1] -- truncating identifiers based on a maximum length provided by the Dialect.  As an example, a quick test that has a variety of uniques produced the constraint names in [2].

My initial strategy took metamodel's ObjectName and modified it to automatically handle name segments and quoting.  For example, `UK_FooClass_1` would be broken down into "UK", "FooClass", and "1" segments, "_" would be the delimiter, and quoting would be added back in whenever necessary.

I'm trying to find a decent strategy for truncating the name, either as a whole or with each segment.  The problem that I keep running into is that it's going to be difficult to dynamically ensure that naming collisions are avoided.  For example, if embedded classes are used as entities, you could have 2 constraint names like "UK_OuterClass$InnerClassA_1" and "UK_OuterClass$InnerClassB_1".  If the middle segment is truncated at or before the "$", it won't work.

Should we try to enforce a rule that the "unique bits" be in a specific segment or position?  Alternatively, "truncate" by hashing the name (as we do with FK names now -- of course, no human readability)?  Any other ideas?

Admittedly, I may be overthinking it.  It's primarily the Hibernate-generated constraint names that we need to worry about...

[1] https://hibernate.onjira.com/browse/HHH-1904
[2] https://gist.github.com/brmeyer/bfbc78c770904cc6fca8

Brett Meyer
Red Hat Software Engineer, Hibernate