From 9f397b433735d3fbba83e01601d00a8b96be19a9 Mon Sep 17 00:00:00 2001
From: John Estropia <rommel.estropia@gmail.com>
Date: Mon, 10 Jun 2019 18:34:15 +0900
Subject: [PATCH] Prevent crashing when DataStack is deallocated ahead of
 ListMonitor and child objects

---
 Sources/From.swift        | 12 ++++++++++--
 Sources/ListMonitor.swift | 11 +++++++++--
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/Sources/From.swift b/Sources/From.swift
index e75a1bb..5a9b778 100644
--- a/Sources/From.swift
+++ b/Sources/From.swift
@@ -140,8 +140,16 @@ public struct From<D: DynamicObject> {
     }
     
     internal func applyToFetchRequest<U>(_ fetchRequest: CoreStoreFetchRequest<U>, context: NSManagedObjectContext, applyAffectedStores: Bool = true) throws {
-        
-        fetchRequest.entity = context.parentStack!.entityDescription(for: EntityIdentifier(self.entityClass))!
+
+        guard let parentStack = context.parentStack else {
+
+            CoreStore.log(
+                .warning,
+                message: "Attempted to perform a fetch but the \(cs_typeName(DataStack.self)) has already been deallocated."
+            )
+            throw CoreStoreError.unknown
+        }
+        fetchRequest.entity = parentStack.entityDescription(for: EntityIdentifier(self.entityClass))!
         guard applyAffectedStores else {
             
             return
diff --git a/Sources/ListMonitor.swift b/Sources/ListMonitor.swift
index 9d8ab88..30f134b 100644
--- a/Sources/ListMonitor.swift
+++ b/Sources/ListMonitor.swift
@@ -963,8 +963,15 @@ public final class ListMonitor<D: DynamicObject>: Hashable {
                     
                     return
                 }
-                
-                try! newFetchedResultsController.performFetchFromSpecifiedStores()
+                do {
+
+                    try newFetchedResultsController.performFetchFromSpecifiedStores()
+                }
+                catch {
+
+                    // DataStack may have been deallocated
+                    return
+                }
                 self.fetchedResultsControllerDelegate.taskGroup.notify(queue: .main) {
                     
                     self.fetchedResultsControllerDelegate.enabled = false