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from psqlextra.backend.migrations.state import PostgresHashPartitionState
from .partition import PostgresPartitionOperation
class PostgresAddHashPartition(PostgresPartitionOperation):
"""Adds a new hash partition to a :see:PartitionedPostgresModel.
Each partition will hold the rows for which the hash value of the
partition key divided by the specified modulus will produce the
specified remainder.
"""
def __init__(
self, model_name: str, name: str, modulus: int, remainder: int
):
"""Initializes new instance of :see:AddHashPartition.
Arguments:
model_name:
The name of the :see:PartitionedPostgresModel.
name:
The name to give to the new partition table.
modulus:
Integer value by which the key is divided.
remainder:
The remainder of the hash value when divided by modulus.
"""
super().__init__(model_name, name)
self.modulus = modulus
self.remainder = remainder
def state_forwards(self, app_label, state):
model = state.models[(app_label, self.model_name_lower)]
model.add_partition(
PostgresHashPartitionState(
app_label=app_label,
model_name=self.model_name,
name=self.name,
modulus=self.modulus,
remainder=self.remainder,
)
)
state.reload_model(app_label, self.model_name_lower)
def database_forwards(self, app_label, schema_editor, from_state, to_state):
model = to_state.apps.get_model(app_label, self.model_name)
if self.allow_migrate_model(schema_editor.connection.alias, model):
schema_editor.add_hash_partition(
model, self.name, self.modulus, self.remainder
)
def database_backwards(
self, app_label, schema_editor, from_state, to_state
):
model = from_state.apps.get_model(app_label, self.model_name)
if self.allow_migrate_model(schema_editor.connection.alias, model):
schema_editor.delete_partition(model, self.name)
def deconstruct(self):
name, args, kwargs = super().deconstruct()
kwargs["modulus"] = self.modulus
kwargs["remainder"] = self.remainder
return name, args, kwargs
def describe(self) -> str:
return "Creates hash partition %s on %s" % (self.name, self.model_name)
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