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import django
from django.db.models.indexes import Index
class ConditionalUniqueIndex(Index):
"""Creates a partial unique index based on a given condition.
Useful, for example, if you need unique combination of foreign keys, but you might want to include
NULL as a valid value. In that case, you can just use:
>>> class Meta:
>>> indexes = [
>>> ConditionalUniqueIndex(fields=['a', 'b', 'c'], condition='"c" IS NOT NULL'),
>>> ConditionalUniqueIndex(fields=['a', 'b'], condition='"c" IS NULL')
>>> ]
"""
sql_create_index = "CREATE UNIQUE INDEX %(name)s ON %(table)s (%(columns)s)%(extra)s WHERE %(condition)s"
def __init__(self, condition: str, fields=[], name=None):
"""Initializes a new instance of :see:ConditionalUniqueIndex."""
super().__init__(fields=fields, name=name)
self._condition = condition
def create_sql(self, model, schema_editor, using="", **kwargs):
"""Creates the actual SQL used when applying the migration."""
if django.VERSION >= (2, 0):
statement = super().create_sql(model, schema_editor, using)
statement.template = self.sql_create_index
statement.parts["condition"] = self._condition
return statement
else:
sql_create_index = self.sql_create_index
sql_parameters = {
**Index.get_sql_create_template_values(
self, model, schema_editor, using
),
"condition": self._condition,
}
return sql_create_index % sql_parameters
def deconstruct(self):
"""Serializes the :see:ConditionalUniqueIndex for the migrations
file."""
path = "%s.%s" % (self.__class__.__module__, self.__class__.__name__)
path = path.replace("django.db.models.indexes", "django.db.models")
return (
path,
(),
{
"fields": self.fields,
"name": self.name,
"condition": self._condition,
},
)
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