[#78] Support app multi KB's

backend/alembic/versions/f8923ed188f1_create_app_knowledge_bases_table_and_migrate_data.py

@@ -0,0 +1,125 @@
+"""create app_knowledge_bases table and migrate data
+
+Revision ID: f8923ed188f1
+Revises: 9c130e8c6c92
+Create Date: 2025-11-03 19:19:44.709923
+"""
+
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy import text
+
+
+# revision identifiers, used by Alembic.
+revision: str = "f8923ed188f1"
+down_revision: Union[str, None] = "9c130e8c6c92"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade():
+    # 1️⃣ Create new table
+    op.create_table(
+        "app_knowledge_bases",
+        sa.Column("id", sa.Integer(), primary_key=True),
+        sa.Column(
+            "app_id",
+            sa.Integer(),
+            sa.ForeignKey("apps.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column("knowledge_base_id", sa.Integer(), nullable=False),
+        sa.Column(
+            "is_default",
+            sa.Boolean(),
+            nullable=False,
+            server_default=sa.text("0"),
+        ),
+        sa.Column(
+            "created_at",
+            sa.DateTime(),
+            nullable=False,
+        ),
+        sa.Column(
+            "updated_at",
+            sa.DateTime(),
+            nullable=False,
+        ),
+        sa.UniqueConstraint("app_id", "knowledge_base_id", name="uq_app_kb"),
+    )
+
+    # 2️⃣ Add a generated virtual column to enforce only one default KB per app
+    op.execute(
+        text(
+            """
+            ALTER TABLE app_knowledge_bases
+            ADD COLUMN unique_default_app_id INT
+            GENERATED ALWAYS AS (
+                CASE WHEN is_default = 1 THEN app_id ELSE NULL END
+            ) VIRTUAL,
+            ADD UNIQUE INDEX uq_app_default_kb_per_app (unique_default_app_id);
+            """
+        )
+    )
+
+    # 3️⃣ Migrate existing data from apps.knowledge_base_id
+    conn = op.get_bind()
+    conn.execute(
+        text(
+            """
+            INSERT INTO app_knowledge_bases (
+                app_id, knowledge_base_id, is_default,
+                created_at, updated_at
+            )
+            SELECT id, knowledge_base_id, TRUE, NOW(), NOW()
+            FROM apps
+            WHERE knowledge_base_id IS NOT NULL;
+            """
+        )
+    )
+
+    # 4️⃣ Drop old column from apps
+    op.drop_column("apps", "knowledge_base_id")
+
+
+def downgrade():
+    # 1️⃣ Re-add the old column
+    op.add_column(
+        "apps", sa.Column("knowledge_base_id", sa.Integer(), nullable=True)
+    )
+
+    # 2️⃣ Restore default KB relationships from app_knowledge_bases
+    conn = op.get_bind()
+    conn.execute(
+        text(
+            """
+            UPDATE apps
+            JOIN (
+                SELECT akb.app_id,
+                    COALESCE(
+                        MAX(CASE WHEN akb.is_default = TRUE THEN akb.knowledge_base_id END),
+                        MAX(akb.knowledge_base_id)
+                    ) AS knowledge_base_id
+                FROM app_knowledge_bases akb
+                GROUP BY akb.app_id
+            ) AS sub ON apps.id = sub.app_id
+            SET apps.knowledge_base_id = sub.knowledge_base_id;
+            """
+        )
+    )
+
+    # 3️⃣ Drop unique index and virtual column
+    op.execute(
+        text(
+            """
+            ALTER TABLE app_knowledge_bases
+            DROP INDEX uq_app_default_kb_per_app,
+            DROP COLUMN unique_default_app_id;
+            """
+        )
+    )
+
+    # 4️⃣ Drop table
+    op.drop_table("app_knowledge_bases")