from django.db.backends.ddl_references import Statement, Table
from django.db.models import F, Q
from django.db.models.constraints import BaseConstraint
from django.db.models.sql import Query
__all__ = ['ExclusionConstraint']
[docs]class ExclusionConstraint(BaseConstraint):
template = 'CONSTRAINT %(name)s EXCLUDE USING %(index_type)s (%(expressions)s)%(where)s'
def __init__(self, *, name, expressions, index_type=None, condition=None):
if index_type and index_type.lower() not in {'gist', 'spgist'}:
raise ValueError(
'Exclusion constraints only support GiST or SP-GiST indexes.'
)
if not expressions:
raise ValueError(
'At least one expression is required to define an exclusion '
'constraint.'
)
if not all(
isinstance(expr, (list, tuple)) and len(expr) == 2
for expr in expressions
):
raise ValueError('The expressions must be a list of 2-tuples.')
if not isinstance(condition, (type(None), Q)):
raise ValueError(
'ExclusionConstraint.condition must be a Q instance.'
)
self.expressions = expressions
self.index_type = index_type or 'GIST'
self.condition = condition
super().__init__(name=name)
def _get_expression_sql(self, compiler, connection, query):
expressions = []
for expression, operator in self.expressions:
if isinstance(expression, str):
expression = F(expression)
expression = expression.resolve_expression(query=query)
sql, params = expression.as_sql(compiler, connection)
expressions.append('%s WITH %s' % (sql % params, operator))
return expressions
def _get_condition_sql(self, compiler, schema_editor, query):
if self.condition is None:
return None
where = query.build_where(self.condition)
sql, params = where.as_sql(compiler, schema_editor.connection)
return sql % tuple(schema_editor.quote_value(p) for p in params)
def constraint_sql(self, model, schema_editor):
query = Query(model, alias_cols=False)
compiler = query.get_compiler(connection=schema_editor.connection)
expressions = self._get_expression_sql(compiler, schema_editor.connection, query)
condition = self._get_condition_sql(compiler, schema_editor, query)
return self.template % {
'name': schema_editor.quote_name(self.name),
'index_type': self.index_type,
'expressions': ', '.join(expressions),
'where': ' WHERE (%s)' % condition if condition else '',
}
def create_sql(self, model, schema_editor):
return Statement(
'ALTER TABLE %(table)s ADD %(constraint)s',
table=Table(model._meta.db_table, schema_editor.quote_name),
constraint=self.constraint_sql(model, schema_editor),
)
def remove_sql(self, model, schema_editor):
return schema_editor._delete_constraint_sql(
schema_editor.sql_delete_check,
model,
schema_editor.quote_name(self.name),
)
def deconstruct(self):
path, args, kwargs = super().deconstruct()
kwargs['expressions'] = self.expressions
if self.condition is not None:
kwargs['condition'] = self.condition
if self.index_type.lower() != 'gist':
kwargs['index_type'] = self.index_type
return path, args, kwargs
def __eq__(self, other):
if isinstance(other, self.__class__):
return (
self.name == other.name and
self.index_type == other.index_type and
self.expressions == other.expressions and
self.condition == other.condition
)
return super().__eq__(other)
def __repr__(self):
return '<%s: index_type=%s, expressions=%s%s>' % (
self.__class__.__qualname__,
self.index_type,
self.expressions,
'' if self.condition is None else ', condition=%s' % self.condition,
)
Apr 15, 2020