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Fixed #9253 -- Modified the method used to generate constraint names so that it is consistent regardless of machine word size. 

NOTE: This change is backwards incompatible for some users.

If you are using a 32-bit platform, you will observe no differences as a
result of this change. However, users on 64-bit platforms may experience
some problems using the `reset` management command.

Prior to this change, 64-bit platforms would generate a 64-bit, 16 character
digest in the constraint name; for example:

ALTER TABLE `myapp_sometable` ADD CONSTRAINT `object_id_refs_id_5e8f10c132091d1e` FOREIGN KEY ...

Following this change, all platforms, regardless of word size, will
generate a 32-bit, 8 character digest in the constraint name; for example:

ALTER TABLE `myapp_sometable` ADD CONSTRAINT `object_id_refs_id_32091d1e` FOREIGN KEY ...

As a result of this change, you will not be able to use the `reset`
management command on any table created with 64-bit constraints. This
is because the the new generated name will not match the historically
generated name; as a result, the SQL constructed by the `reset` command
will be invalid.

If you need to reset an application that was created with 64-bit
constraints, you will need to manually drop the old constraint prior
to invoking `reset`.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@10966 bcc190cf-cafb-0310-a4f2-bffc1f526a37
This commit is contained in:
Russell Keith-Magee 2009-06-09 12:59:41 +00:00
parent 031385e4cc
commit 64be8f29d5
1 changed files with 7 additions and 4 deletions
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11
django/db/backends/creation.py
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@ -25,6 +25,10 @@ class BaseDatabaseCreation(object):
def __init__(self, connection):
self.connection = connection
def _digest(self, *args):
"Generate a 32 bit digest of a set of arguments that can be used to shorten identifying names"
return '%x' % (abs(hash(args)) % (1<<32))
def sql_create_model(self, model, style, known_models=set()):
"""
Returns the SQL required to create a single model, as a tuple of:
@ -128,7 +132,7 @@ class BaseDatabaseCreation(object):
col = opts.get_field(f.rel.field_name).column
# For MySQL, r_name must be unique in the first 64 characters.
# So we are careful with character usage here.
r_name = '%s_refs_%s_%x' % (r_col, col, abs(hash((r_table, table))))
r_name = '%s_refs_%s_%s' % (r_col, col, self._digest(r_table, table))
final_output.append(style.SQL_KEYWORD('ALTER TABLE') + ' %s ADD CONSTRAINT %s FOREIGN KEY (%s) REFERENCES %s (%s)%s;' % \
(qn(r_table), qn(truncate_name(r_name, self.connection.ops.max_name_length())),
qn(r_col), qn(table), qn(col),
@ -187,8 +191,7 @@ class BaseDatabaseCreation(object):
output.append('\n'.join(table_output))
for r_table, r_col, table, col in deferred:
r_name = '%s_refs_%s_%x' % (r_col, col,
abs(hash((r_table, table))))
r_name = '%s_refs_%s_%s' % (r_col, col, self._digest(r_table, table))
output.append(style.SQL_KEYWORD('ALTER TABLE') + ' %s ADD CONSTRAINT %s FOREIGN KEY (%s) REFERENCES %s (%s)%s;' %
(qn(r_table),
qn(truncate_name(r_name, self.connection.ops.max_name_length())),
@ -289,7 +292,7 @@ class BaseDatabaseCreation(object):
col = f.column
r_table = model._meta.db_table
r_col = model._meta.get_field(f.rel.field_name).column
r_name = '%s_refs_%s_%x' % (col, r_col, abs(hash((table, r_table))))
r_name = '%s_refs_%s_%s' % (col, r_col, self._digest(table, r_table))
output.append('%s %s %s %s;' % \
(style.SQL_KEYWORD('ALTER TABLE'),
style.SQL_TABLE(qn(table)),