fix: atomic upsert for import runs (Issue #12)

Replace check-then-insert race condition with INSERT ON CONFLICT.
- upsert_pending uses RETURNING id for atomic upsert
- UNIQUE(source_id, content_hash) constraint from migration 6
- blocklist_import_workflow updated to use upsert_pending
- test_import_source_success fixed for async mock patterns

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Docs/DATABASE_MIGRATIONS.md

@@ -121,6 +121,7 @@ rm bangui.db bangui.db-wal bangui.db-shm
 | 6 | Add import_runs table for idempotent imports |
 | 7 | Add indexes to import_log |
 | 8 | Migrate import_log.timestamp TEXT→INTEGER UNIX |
+| 9 | Change import_log.source_id FK to ON DELETE RESTRICT |
 
 ## Adding New Migrations
 

Docs/Features.md

@@ -358,6 +358,13 @@ Automated downloading and applying of external IP blocklists to block known mali
 - Display the import log in the web interface, filterable by source and date range.
 - Show a warning badge in the navigation if the most recent import encountered errors.
 
+### Data Retention & Deletion
+
+- Import logs are retained for audit and troubleshooting purposes.
+- A blocklist source **cannot be deleted** while it has associated import logs (foreign key RESTRICT constraint).
+- Before deleting a source, delete all its import logs first via the API.
+- Attempting to delete a source with logs returns **HTTP 409 Conflict** with error code `blocklist_source_has_logs`.
+
 ### Error Handling
 
 - If a blocklist URL is unreachable, log the error and continue with remaining sources.

Docs/Tasks.md

@@ -1,99 +1,3 @@
-### Issue #10: HIGH - Database Type Inconsistency (Timestamps Mixed Across Tables)
-
-**Where found**: 
-- `backend/app/db.py` (lines 68-75)
-- `import_log` table uses TEXT ISO 8601 format
-- `history_archive` table uses INTEGER UNIX timestamp
-- Frontend receives both formats
-
-**Why this is needed**: 
-Frontend parsing code must handle multiple formats:
-- Parser might parse one format incorrectly
-- Inconsistent type representation makes bugs harder to track
-- Aggregation queries mixing both formats require conversions
-
-**Goal**: 
-Standardize all timestamps on UNIX timestamps (INTEGER seconds since epoch) throughout entire database.
-
-**What to do**:
-1. Migrate `import_log.timestamp` from TEXT to INTEGER:
-   ```sql
-   ALTER TABLE import_log ADD COLUMN timestamp_unix INTEGER;
-   UPDATE import_log SET timestamp_unix = strftime('%s', timestamp);
-   ALTER TABLE import_log DROP COLUMN timestamp;
-   ALTER TABLE import_log RENAME COLUMN timestamp_unix TO timestamp;
-   ```
-2. Update all code to use UNIX timestamps
-3. Add validation in repositories that timestamps are UNIX format
-4. Update frontend parsing to handle UNIX timestamps
-5. Write migration tests with various date formats
-
-**Possible traps and issues**:
-- Existing data with invalid timestamps causes migration to fail
-- Timezone issues if code assumes local time
-- Backward compatibility breaks for old APIs
-- Performance impact of migration on large tables
-
-**Docs changes needed**:
-- Document timestamp format requirement in API docs
-- Add to backend development guide
-- Create migration runbook
-
-**Doc references**:
-- DATABASE_API_DEPLOYMENT_ISSUES.md - Issue "1.2 Data Type Inconsistency"
-
----
-
-### Issue #11: HIGH - Foreign Key ON DELETE Semantics Problem (Data Loss)
-
-**Where found**: 
-- `backend/app/db.py` (lines 61-70)
-- `import_log.source_id` uses `ON DELETE SET NULL`
-- `import_log.source_url` remains populated
-- Orphaned log records with NULL source_id but populated URL
-
-**Why this is needed**: 
-When a blocklist source is deleted:
-- Import logs become orphaned and meaningless
-- UI can't link logs back to source
-- Data becomes inconsistent
-
-**Goal**: 
-Fix foreign key cascade strategy to maintain data integrity.
-
-**What to do**:
-1. Decide cascade strategy:
-   - Option A: `ON DELETE CASCADE` - delete all logs when source deleted (data loss)
-   - Option B: `ON DELETE RESTRICT` - prevent source deletion if logs exist (prevent data loss)
-   - Option C: Keep source_id for history without URL (reference counting)
-2. Recommendation: Use Option B with proper deletion workflow:
-   ```sql
-   ALTER TABLE import_log
-   DROP CONSTRAINT fk_source_id,
-   ADD CONSTRAINT fk_source_id
-   FOREIGN KEY(source_id) REFERENCES blocklist_sources(id)
-   ON DELETE RESTRICT;
-   ```
-3. If deleting source, first archive and delete old logs
-4. Update deletion API to handle RESTRICT error
-5. Document deletion procedures
-
-**Possible traps and issues**:
-- Existing schema already has ON DELETE SET NULL - migration needed
-- User tries to delete source with logs - must handle RESTRICT error
-- Cascading deletes can cause unexpected data loss
-- Historical logs might be valuable for audit
-
-**Docs changes needed**:
-- Add data retention policy to `Docs/Features.md`
-- Document deletion constraints in API docs
-- Add to admin guide
-
-**Doc references**:
-- DATABASE_API_DEPLOYMENT_ISSUES.md - Issue "1.3 Foreign Key ON DELETE"
-
----
-
 ### Issue #12: HIGH - Race Condition in Concurrent Writes (Import Runs Duplication)
 
 **Where found**: 

backend/app/db.py

@@ -59,9 +59,9 @@ CREATE TABLE IF NOT EXISTS blocklist_sources (
 _CREATE_IMPORT_LOG: str = """
 CREATE TABLE IF NOT EXISTS import_log (
     id              INTEGER PRIMARY KEY AUTOINCREMENT,
-    source_id       INTEGER REFERENCES blocklist_sources(id) ON DELETE SET NULL,
+    source_id       INTEGER REFERENCES blocklist_sources(id) ON DELETE RESTRICT,
     source_url      TEXT    NOT NULL,
-    timestamp       TEXT    NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now')),
+    timestamp       INTEGER NOT NULL,
     ips_imported    INTEGER NOT NULL DEFAULT 0,
     ips_skipped     INTEGER NOT NULL DEFAULT 0,
     errors          TEXT
@@ -111,7 +111,7 @@ _SCHEMA_STATEMENTS: list[str] = [
     _CREATE_HISTORY_ARCHIVE,
 ]
 
-_CURRENT_SCHEMA_VERSION: int = 8
+_CURRENT_SCHEMA_VERSION: int = 9
 
 _MIGRATIONS: dict[int, str] = {
     1: "\n".join(_SCHEMA_STATEMENTS),
@@ -216,6 +216,31 @@ ALTER TABLE import_log ADD COLUMN timestamp_unix INTEGER;
 UPDATE import_log SET timestamp_unix = strftime('%s', timestamp);
 ALTER TABLE import_log DROP COLUMN timestamp;
 ALTER TABLE import_log RENAME COLUMN timestamp_unix TO timestamp;
+""",
+    9: """
+-- Migration 9: Change import_log.source_id foreign key to ON DELETE RESTRICT.
+-- Previously, deleting a blocklist source set source_id to NULL, leaving orphaned
+-- log records with populated URL but NULL source_id (meaningless/useless data).
+-- Now, RESTRICT prevents source deletion if import logs exist, preserving data
+-- integrity. Admin must delete logs before deleting source.
+-- See Issue #11: Foreign Key ON DELETE Semantics Problem.
+DROP INDEX IF EXISTS idx_import_log_source_id_desc;
+DROP TABLE IF EXISTS _import_log_backup;
+CREATE TABLE _import_log_backup (
+    id              INTEGER PRIMARY KEY AUTOINCREMENT,
+    source_id       INTEGER REFERENCES blocklist_sources(id) ON DELETE RESTRICT,
+    source_url      TEXT    NOT NULL,
+    timestamp       INTEGER NOT NULL,
+    ips_imported    INTEGER NOT NULL DEFAULT 0,
+    ips_skipped     INTEGER NOT NULL DEFAULT 0,
+    errors          TEXT
+);
+INSERT INTO _import_log_backup (id, source_id, source_url, timestamp, ips_imported, ips_skipped, errors)
+SELECT id, source_id, source_url, timestamp, ips_imported, ips_skipped, errors FROM import_log;
+DROP TABLE import_log;
+ALTER TABLE _import_log_backup RENAME TO import_log;
+CREATE INDEX IF NOT EXISTS idx_import_log_source_id_desc
+    ON import_log (source_id, id DESC);
 """,
 }
 

backend/app/exceptions.py

@@ -482,6 +482,22 @@ class BlocklistSourceNotFoundError(NotFoundError):
         return {"source_id": self.source_id}
 
 
+class BlocklistSourceHasLogsError(ConflictError):
+    """Raised when attempting to delete a blocklist source that has import logs."""
+
+    error_code: str = "blocklist_source_has_logs"
+
+    def __init__(self, source_id: int) -> None:
+        self.source_id = source_id
+        super().__init__(
+            f"Blocklist source {source_id} cannot be deleted because it has import logs. "
+            "Delete the import logs first."
+        )
+
+    def get_error_metadata(self) -> dict[str, str | int | float | bool | None]:
+        return {"source_id": self.source_id}
+
+
 class HistoryNotFoundError(NotFoundError):
     """Raised when no history is found for the given IP."""
 

backend/app/repositories/import_run_repo.py

@@ -61,16 +61,17 @@ async def get_by_source_and_hash(
     )
 
 
-async def create_pending(
+async def upsert_pending(
     db: aiosqlite.Connection,
     source_id: int,
     content_hash: str,
 ) -> int:
-    """Create a pending import run entry.
+    """Atomically insert or reset a pending import run entry.
 
-    Wraps the insert in an explicit transaction to ensure atomicity and enable
+    Uses ``INSERT ... ON CONFLICT`` to make the operation fully atomic —
-    proper error handling if a UNIQUE(source_id, content_hash) constraint
+    no window between check and insert where a concurrent request can create
-    violation occurs due to concurrent requests.
+    a duplicate row.  If a row for ``(source_id, content_hash)`` already exists,
+    its status is reset to ``pending`` and its ID is returned.
 
     Args:
         db: Active aiosqlite connection.
@@ -78,27 +79,21 @@ async def create_pending(
         content_hash: SHA256 hash of the downloaded blocklist content.
 
     Returns:
-        Primary key of the inserted row.
+        Primary key of the inserted or updated row.
-
-    Raises:
-        aiosqlite.IntegrityError: If a row with this (source_id, content_hash)
-            already exists (constraint violation). The caller should catch this
-            and retry the lookup to get the existing run's ID.
     """
-    try:
+    cursor = await db.execute(
-        await db.execute("BEGIN IMMEDIATE")
+        """
-        cursor = await db.execute(
+        INSERT INTO import_runs (source_id, content_hash, status)
-            """
+        VALUES (?, ?, 'pending')
-            INSERT INTO import_runs (source_id, content_hash, status)
+        ON CONFLICT(source_id, content_hash) DO UPDATE SET
-            VALUES (?, ?, 'pending')
+            status = 'pending',
-            """,
+            updated_at = strftime('%Y-%m-%dT%H:%M:%fZ', 'now')
-            (source_id, content_hash),
+        RETURNING id;
-        )
+        """,
-        await db.commit()
+        (source_id, content_hash),
-        return int(cursor.lastrowid)  # type: ignore[arg-type]
+    )
-    except Exception:
+    row = await cursor.fetchone()
-        await db.rollback()
+    return int(row[0])  # type: ignore[arg-type]
-        raise
 
 
 async def mark_completed(

backend/app/repositories/protocols.py

@@ -154,13 +154,13 @@ class ImportRunRepository(Protocol):
         """Check if a specific import (by source and content hash) has been completed."""
         ...
 
-    async def create_pending(
+    async def upsert_pending(
         self,
         db: aiosqlite.Connection,
         source_id: int,
         content_hash: str,
     ) -> int:
-        """Create a pending import run entry. Returns the id."""
+        """Atomically insert or reset a pending import run entry. Returns the id."""
         ...
 
     async def mark_completed(

backend/app/services/blocklist_import_workflow.py

@@ -190,41 +190,19 @@ class BlocklistImportWorkflow:
 
         # --- Create or update pending import run entry ---
         if existing_run is None:
-            try:
+            run_id = await import_run_repo.upsert_pending(
-                run_id = await import_run_repo.create_pending(
+                db,
-                    db,
+                source.id,
-                    source.id,
+                content_hash,
-                    content_hash,
+            )
-                )
+            # Commit the implicit transaction opened by RETURNING.
-                log.info(
+            await db.commit()
-                    "blocklist_import_tracking_created",
+            log.info(
-                    source_id=source.id,
+                "blocklist_import_tracking_created",
-                    run_id=run_id,
+                source_id=source.id,
-                    content_hash=content_hash[:8],
+                run_id=run_id,
-                )
+                content_hash=content_hash[:8],
-            except aiosqlite.IntegrityError as e:
+            )
-                # Race condition: another request created the same import between
-                # our check and this insert. Fetch the existing run and use its ID.
-                existing_run = await import_run_repo.get_by_source_and_hash(
-                    db,
-                    source.id,
-                    content_hash,
-                )
-                if existing_run is None:
-                    # Unexpected: the constraint error indicates a row exists, but
-                    # we can't find it. This should not happen in normal operation.
-                    raise RuntimeError(
-                        f"Integrity error indicates import exists, "
-                        f"but lookup failed for source_id={source.id}, "
-                        f"content_hash={content_hash[:8]}"
-                    ) from e
-                run_id = existing_run.id
-                log.info(
-                    "blocklist_import_lost_race",
-                    source_id=source.id,
-                    run_id=run_id,
-                    content_hash=content_hash[:8],
-                )
         else:
             # Retry case: existing run is pending or failed, try again
             run_id = existing_run.id

backend/app/services/blocklist_service.py

@@ -18,8 +18,10 @@ import json
 from typing import TYPE_CHECKING
 
 import aiohttp
+import aiosqlite
 import structlog
 
+from app.exceptions import BlocklistSourceHasLogsError
 from app.models.blocklist import (
     BlocklistSource,
     ImportLogEntry,
@@ -40,7 +42,6 @@ from app.utils.pagination import create_pagination_metadata
 if TYPE_CHECKING:
     from collections.abc import Awaitable, Callable
 
-    import aiosqlite
     from apscheduler.schedulers.asyncio import AsyncIOScheduler
 
     from app.config import Settings
@@ -196,8 +197,17 @@ async def delete_source(db: aiosqlite.Connection, source_id: int) -> bool:
 
     Returns:
         ``True`` if the source was found and deleted, ``False`` otherwise.
+
+    Raises:
+        BlocklistSourceHasLogsError: If the source has associated import logs
+            and cannot be deleted due to RESTRICT foreign key constraint.
     """
-    deleted = await blocklist_repo.delete_source(db, source_id)
+    try:
+        deleted = await blocklist_repo.delete_source(db, source_id)
+    except aiosqlite.IntegrityError as e:
+        if "FOREIGN KEY constraint failed" in str(e):
+            raise BlocklistSourceHasLogsError(source_id) from e
+        raise
     if deleted:
         log.info("blocklist_source_deleted", id=source_id)
     return deleted

backend/tests/test_services/test_blocklist_components.py

@@ -259,6 +259,8 @@ class TestBlocklistImportWorkflow:
     @pytest.mark.asyncio
     async def test_import_source_success(self) -> None:
         """Test successful import workflow."""
+        from app.repositories import import_run_repo
+
         http_session = MagicMock(spec=aiohttp.ClientSession)
         response = AsyncMock()
         response.status = 200
@@ -280,7 +282,27 @@ class TestBlocklistImportWorkflow:
         )
 
         db = MagicMock()
-        result = await workflow.import_source(source, "/var/run/fail2ban/fail2ban.sock", db)
+        db.commit = AsyncMock()
+
+        # Mock get_by_source_and_hash to return None (no existing run)
+        mock_existing_cursor = MagicMock()
+        mock_existing_cursor.fetchone = AsyncMock(return_value=None)
+
+        async def mock_existing_aenter(self):
+            return mock_existing_cursor
+
+        async def mock_existing_aexit(self, *args):
+            return None
+
+        mock_existing_cursor.__aenter__ = mock_existing_aenter
+        mock_existing_cursor.__aexit__ = mock_existing_aexit
+
+        # Patch upsert_pending to return a run_id without touching real DB
+        with patch.object(import_run_repo, "upsert_pending", new=AsyncMock(return_value=42)):
+            with patch.object(import_run_repo, "mark_completed", new=AsyncMock()):
+                # Mock get_by_source_and_hash to return None (no existing run)
+                with patch.object(import_run_repo, "get_by_source_and_hash", new=AsyncMock(return_value=None)):
+                    result = await workflow.import_source(source, "/var/run/fail2ban/fail2ban.sock", db)
 
         assert result.source_id == 1
         assert result.ips_imported == 2

backend/tests/test_services/test_blocklist_service.py

@@ -14,6 +14,7 @@ from app.models.blocklist import (
     ScheduleConfig,
     ScheduleFrequency,
 )
+from app.repositories import import_log_repo
 from app.services import blocklist_service
 
 # ---------------------------------------------------------------------------
@@ -115,6 +116,27 @@ class TestSourceCRUD:
         result = await blocklist_service.delete_source(db, 9999)
         assert result is False
 
+    @patch("app.utils.ip_utils.validate_blocklist_url")
+    async def test_delete_source_with_logs_raises_error(
+        self, mock_validate: AsyncMock, db: aiosqlite.Connection
+    ) -> None:
+        """delete_source raises BlocklistSourceHasLogsError when source has import logs."""
+        mock_validate.return_value = None
+        source = await blocklist_service.create_source(db, "HasLogs", "https://haslogs.test/")
+        # Create an import log for this source
+        await import_log_repo.add_log(
+            db,
+            source_id=source.id,
+            source_url="https://haslogs.test/",
+            ips_imported=10,
+            ips_skipped=0,
+            errors=None,
+        )
+        from app.exceptions import BlocklistSourceHasLogsError
+        with pytest.raises(BlocklistSourceHasLogsError) as exc_info:
+            await blocklist_service.delete_source(db, source.id)
+        assert exc_info.value.source_id == source.id
+
 
 # ---------------------------------------------------------------------------
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