def check(self, against, using=DEFAULT_DB_ALIAS):
"""
Do a database query to check if the expressions of the Q instance
matches against the expressions.
"""
# Avoid circular imports.
from django.db.models import Value
from django.db.models.sql import Query
from django.db.models.sql.constants import SINGLE
query = Query(None)
for name, value in against.items():
if not hasattr(value, "resolve_expression"):
value = Value(value)
query.add_annotation(value, name, select=False)
query.add_annotation(Value(1), "_check")
# This will raise a FieldError if a field is missing in "against".
query.add_q(self)
compiler = query.get_compiler(using=using)
try:
return compiler.execute_sql(SINGLE) is not None
except DatabaseError as e:
logger.warning("Got a database error calling check() on %r: %s",
self, e)
return True
def _get_check_sql(self, model, schema_editor):
query = Query(model=model)
# Add annotations
for k, v in self.annotations.items():
query.add_annotation(v, k)
where = query.build_where(self.check)
compiler = query.get_compiler(connection=schema_editor.connection)
sql, params = where.as_sql(compiler, schema_editor.connection)
return sql % tuple(schema_editor.quote_value(p) for p in params)
