Implement many-to-many movie sharing

backend/backlog_app/alembic/versions/2026_08_23_0001-a1b2c3d4e5f6_add_user_movies_table.py

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+"""add user_movies table
+
+Revision ID: a1b2c3d4e5f6
+Revises: 4dc9128d633a
+Create Date: 2026-08-23 00:01:00.000000
+
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+from sqlalchemy.dialects import postgresql
+
+# revision identifiers, used by Alembic.
+revision: str = "a1b2c3d4e5f6"
+down_revision: Union[str, Sequence[str], None] = "4dc9128d633a"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    # 1. Create user_movies table
+    op.create_table(
+        "user_movies",
+        sa.Column("id", sa.Integer(), autoincrement=True, nullable=False),
+        sa.Column("user_id", postgresql.UUID(as_uuid=True), nullable=False),
+        sa.Column("movie_id", sa.Integer(), nullable=False),
+        sa.Column("watched", sa.Boolean(), server_default="false", nullable=False),
+        sa.Column("note", sa.String(length=50), nullable=True),
+        sa.Column("rating", sa.Float(), nullable=True),
+        sa.Column(
+            "joined_at",
+            sa.DateTime(timezone=True),
+            server_default=sa.text("now()"),
+            nullable=False,
+        ),
+        sa.ForeignKeyConstraint(["movie_id"], ["movies.id"], ondelete="CASCADE"),
+        sa.ForeignKeyConstraint(["user_id"], ["user.id"], ondelete="CASCADE"),
+        sa.PrimaryKeyConstraint("id"),
+        sa.UniqueConstraint("user_id", "movie_id", name="uq_user_movie"),
+    )
+
+    # 2. Migrate existing movie data into user_movies
+    op.execute("""
+        INSERT INTO user_movies (user_id, movie_id, watched, note, rating, joined_at)
+        SELECT user_id, id, watched, note, rating, created_at
+        FROM movies
+        """)
+
+    # 3. Drop watched, note, rating from movies
+    op.drop_column("movies", "watched")
+    op.drop_column("movies", "note")
+    op.drop_column("movies", "rating")
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    # 1. Re-add columns to movies
+    op.add_column(
+        "movies",
+        sa.Column("watched", sa.Boolean(), server_default="false", nullable=False),
+    )
+    op.add_column(
+        "movies",
+        sa.Column("note", sa.String(length=50), nullable=True),
+    )
+    op.add_column(
+        "movies",
+        sa.Column("rating", sa.Float(), nullable=True),
+    )
+
+    # 2. Restore data from user_movies (owner's row)
+    op.execute("""
+        UPDATE movies
+        SET
+            watched = um.watched,
+            note = um.note,
+            rating = um.rating
+        FROM user_movies um
+        WHERE um.movie_id = movies.id
+          AND um.user_id = movies.user_id
+        """)
+
+    # 3. Drop user_movies table
+    op.drop_table("user_movies")