105 lines
4.4 KiB
Python
105 lines
4.4 KiB
Python
"""add uuid column to meter table
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Adds a stable ``uuid`` (UUID v4 string) column to the ``meter`` table so that
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each meter epoch has a durable identity anchor suitable for use as an HA
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Discovery ``unique_id``.
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**Migration strategy (SQLite-safe)**:
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SQLite does not support adding a NOT NULL + UNIQUE column to a non-empty table
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in a single ``ALTER TABLE ADD COLUMN`` statement (adding a NOT NULL column
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without a default value is rejected if the table already has rows). The
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safe approach used here is:
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1. Add ``uuid`` as a **nullable** column (SQLite allows this).
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2. **Back-fill** every existing ``meter`` row with a distinct ``str(uuid4())``
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value. Each row gets its *own* random UUID — not a shared value — so the
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subsequent UNIQUE constraint is satisfied.
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3. Use ``batch_alter_table`` (which re-creates the table under the hood in
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SQLite) to alter the column to ``NOT NULL`` and add a UNIQUE constraint.
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**Idempotency**: only rows where ``uuid IS NULL`` are back-filled; rows that
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already have a uuid (e.g. from a repeated upgrade after a partial failure) are
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left untouched.
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**Audit**: after back-fill, the count of rows with ``uuid IS NULL`` must be
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exactly zero; if not, the migration raises ``RuntimeError`` and rolls back.
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**Data safety**: this migration is additive only — no existing rows are deleted
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or overwritten; it only adds a new column and fills it in.
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Revision ID: 20260625_14_meter_uuid
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Revises: 20260625_13_meter_table
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Create Date: 2026-06-25 00:00:00.000000
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"""
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import uuid as _uuid
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from typing import Sequence, Union
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import sqlalchemy as sa
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from alembic import op
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revision: str = "20260625_14_meter_uuid"
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down_revision: Union[str, None] = "20260625_13_meter_table"
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branch_labels: Union[str, Sequence[str], None] = None
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depends_on: Union[str, Sequence[str], None] = None
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def upgrade() -> None:
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conn = op.get_bind()
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# ------------------------------------------------------------------ #
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# 1. Add uuid as a nullable column. #
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# ------------------------------------------------------------------ #
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with op.batch_alter_table("meter", schema=None) as batch_op:
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batch_op.add_column(
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sa.Column("uuid", sa.String(length=36), nullable=True)
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)
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# ------------------------------------------------------------------ #
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# 2. Back-fill: assign a distinct UUID to every row that has #
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# uuid IS NULL. Each row gets its own random value so that the #
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# subsequent UNIQUE constraint is satisfied. #
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# ------------------------------------------------------------------ #
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rows = conn.execute(sa.text("SELECT id FROM meter WHERE uuid IS NULL")).fetchall()
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for (meter_id,) in rows:
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new_uuid = str(_uuid.uuid4())
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conn.execute(
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sa.text("UPDATE meter SET uuid = :uuid WHERE id = :mid"),
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{"uuid": new_uuid, "mid": meter_id},
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)
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# ------------------------------------------------------------------ #
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# 3. Audit: verify no rows remain with uuid IS NULL. #
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# ------------------------------------------------------------------ #
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null_count_row = conn.execute(
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sa.text("SELECT COUNT(*) FROM meter WHERE uuid IS NULL")
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).fetchone()
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null_count: int = null_count_row[0] if null_count_row else 0
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if null_count != 0:
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raise RuntimeError(
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f"meter.uuid back-fill audit failed: {null_count} meter row(s) still have "
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"uuid IS NULL after back-fill. Migration aborted to protect data integrity."
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)
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# ------------------------------------------------------------------ #
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# 4. Alter column to NOT NULL + UNIQUE (requires batch on SQLite). #
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# batch_alter_table re-creates the table, so the UNIQUE constraint #
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# and NOT NULL are applied atomically. #
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# ------------------------------------------------------------------ #
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with op.batch_alter_table("meter", schema=None) as batch_op:
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batch_op.alter_column(
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"uuid",
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existing_type=sa.String(length=36),
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nullable=False,
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)
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batch_op.create_unique_constraint("uq_meter_uuid", ["uuid"])
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def downgrade() -> None:
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# Drop the UNIQUE constraint and the uuid column (batch on SQLite).
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with op.batch_alter_table("meter", schema=None) as batch_op:
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batch_op.drop_constraint("uq_meter_uuid", type_="unique")
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batch_op.drop_column("uuid")
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