HHH-6813 https://hibernate.atlassian.net/browse/HHH-6813 Having an @Id @OneToOne (derived primary key from a foreign key) causes NullPointerExceptions during any query ----------------------------------------------- (All of the following fixes compose a near complete re-write of how Hibernate generates names for unique, foreign, and index constraints that are not explicitly named in mappings. The set should be taken holistically, rather than individually -- most iteratively build on each other.) HHH-1904 (superseded), HHH-8217, HHH-8269 https://hibernate.atlassian.net/browse/HHH-1904 https://hibernate.atlassian.net/browse/HHH-8217 https://hibernate.atlassian.net/browse/HHH-8269 To ensure a maximum identifier length, generate all non-named constraint names by hashing a concatenation of the table name and an alphabetical ordering of column names. HHH-8217 supersedes HHH-1904 with the correct approach. HHH-8092, HHH-8162 https://hibernate.atlassian.net/browse/HHH-8092 https://hibernate.atlassian.net/browse/HHH-8162 The pre-existance of unique constraints cannot be easily/consistently checked within JDBC. Methods for foreign keys and indexes exist, but uniques would require very dialect-specific functions to be used. Instead, allow unique constraint handling during a schema update to be configurable: completely ignore uniques altogether or attempt to (re-)create the constraints and ignore any errors (but include a warning log). HHH-8178 https://hibernate.atlassian.net/browse/HHH-8178 The internal processing of natural keys was corrected to ensure all of its columns were going into a single unique constraint. The hashed name changes, above, had broken it. HHH-8275 https://hibernate.atlassian.net/browse/HHH-8275 Union-subclass inheritance mappings were incorrectly using the parent table name in the unique constraint "alter table" statement, instead of the sub-table. HHH-8273 https://hibernate.atlassian.net/browse/HHH-8273 Corrected "unique-key" documentation to reflect all above changes. -----------------------------------------------