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    <p>Yo guys,</p> <p>I managed to make what I wanted.</p> <p>First, I created a new field:</p> <pre><code>from django.db.models.deletion import DO_NOTHING from django.db.models.fields.related import ForeignKey, ManyToOneRel class SoftForeignKey(ForeignKey): """ This field behaves like a normal django ForeignKey only without hard database constraints. """ def __init__(self, to, to_field=None, rel_class=ManyToOneRel, **kwargs): ForeignKey.__init__(self, to, to_field=to_field, rel_class=rel_class, **kwargs) self.on_delete = DO_NOTHING no_db_constraints = True </code></pre> <p>Since I use South to manage my database schema, I had to add this:</p> <pre><code>from south.modelsinspector import add_introspection_rules add_introspection_rules([], [r'^ecm\.lib\.softfk\.SoftForeignKey']) </code></pre> <p>Then, I had to monkey patch south so that it takes the <code>no_db_constraints</code> parameter into account. There were two functions involved in the creation of FK constraints: </p> <pre><code>from django.db.models.deletion import DO_NOTHING from django.db.models.fields.related import ForeignKey, ManyToOneRel from django.core.management.color import no_style from south.db.generic import DatabaseOperations, invalidate_table_constraints, flatten def column_sql(self, table_name, field_name, field, tablespace='', with_name=True, field_prepared=False): """ Creates the SQL snippet for a column. Used by add_column and add_table. """ # If the field hasn't already been told its attribute name, do so. ... ... ... if field.rel and self.supports_foreign_keys: # HACK: "soft" FK handling begin if not hasattr(field, 'no_db_constraints') or not field.no_db_constraints: self.add_deferred_sql( self.foreign_key_sql( table_name, field.column, field.rel.to._meta.db_table, field.rel.to._meta.get_field(field.rel.field_name).column ) ) # HACK: "soft" FK handling end # Things like the contrib.gis module fields have this in 1.1 and below if hasattr(field, 'post_create_sql'): for stmt in field.post_create_sql(no_style(), ta .... .... # monkey patch South here DatabaseOperations.column_sql = column_sql </code></pre> <p>And:</p> <pre><code>from django.db.models.deletion import DO_NOTHING from django.db.models.fields.related import ForeignKey, ManyToOneRel from django.core.management.color import no_style from south.db.generic import DatabaseOperations, invalidate_table_constraints, flatten @invalidate_table_constraints def alter_column(self, table_name, name, field, explicit_name=True, ignore_constraints=False): """ Alters the given column name so it will match the given field. Note that conversion between the two by the database must be possible. Will not automatically add _id by default; to have this behavour, pass explicit_name=False. @param table_name: The name of the table to add the column to @param name: The name of the column to alter @param field: The new field definition to use """ if self.dry_run: if self.debug: ... ... if not ignore_constraints: # Add back FK constraints if needed if field.rel and self.supports_foreign_keys: # HACK: "soft" FK handling begin if not hasattr(field, 'no_db_constraints') or not field.no_db_constraints: self.execute( self.foreign_key_sql( table_name, field.column, field.rel.to._meta.db_table, field.rel.to._meta.get_field(field.rel.field_name).column ) ) # HACK: "soft" FK handling end # monkey patch South here DatabaseOperations.alter_column = alter_column </code></pre> <p>This is really ugly but I didn't find another way. </p> <p>Now you can use the SoftForeignKey field exactly like a normal ForeignKey except that you won't have any referencial integrity enforcement.</p> <p>See here for the complete monkey-patch : <a href="http://eve-corp-management.org/projects/ecm/repository/entry/ecm/lib/softfk.py" rel="nofollow">http://eve-corp-management.org/projects/ecm/repository/entry/ecm/lib/softfk.py</a></p>
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