change-tracking

Change Tracking

Manages entity states and detects changes for SaveChanges().

Core Components

• StateManager — owns tracked entries, identity/reference maps, fixup, cascades, notifications, and changed counts
• InternalEntryBase and derived classes — own per-entry state, flags, values, snapshots, and ordered state transitions
• ChangeDetector — compares current values with baselines and reports changes through entry mutation APIs
• SnapshotFactoryFactory subclasses — create passive original- and relationship-value baselines
• IdentityMap — permits one active entry per key; shared identity pairs a replacement with the prior Deleted entry
• PropertyAccessorsFactory, ClrPropertyGetterFactory and ClrPropertySetterFactory compile property accessors for efficient snapshotting and change detection
  • Ordinals in indices parameter specify element at each complex collection depth

Change Detection

• Snapshot and notification strategies both call SetPropertyModified() to keep property flags and entity state consistent.
• SetEntityState() validates values, updates flags and complex entries, changes state, then runs manager bookkeeping hooks.

Shared-Identity Replacement

SharedIdentityEntry is the invariant that distinguishes an old deleted entry from its replacement with the same identity. When attaching a replacement graph, a deleted nested entry should be reconsidered only when its source entry has a replacement; do not broadly process every deleted node. Likewise, cascading from the old replaced principal must not delete dependents that belong to the replacement graph. Keep synchronous and asynchronous graph-attach paths equivalent and preserve unrelated values in replacement tests so they isolate the identity transition.

Testing

Unit tests: test/EFCore.Tests/ChangeTracking/. Functional tests: test/EFCore.Specification.Tests/GraphUpdates/.

Common Pitfalls

Pitfall	Solution
State-based checks treat every Added/Deleted entry as a replacement	Scope replacement behavior through SharedIdentityEntry and the graph source

Validation

• DetectChanges() identifies modified properties via snapshot comparison
• Setting original values marks properties as modified or unchanged based on comparison with current values