improved migrationchain validation

CoreStore/Internal/NSManagedObjectModel+Setup.swift

@@ -33,7 +33,7 @@ internal extension NSManagedObjectModel {
     
     // MARK: Internal
     
-    @nonobjc internal class func fromBundle(bundle: NSBundle, modelName: String, modelVersion: String? = nil) -> NSManagedObjectModel {
+    @nonobjc internal class func fromBundle(bundle: NSBundle, modelName: String, modelVersionHints: Set<String> = []) -> NSManagedObjectModel {
         
         guard let modelFilePath = bundle.pathForResource(modelName, ofType: "momd") else {
             
@@ -46,19 +46,34 @@ internal extension NSManagedObjectModel {
         guard let versionInfo = NSDictionary(contentsOfURL: versionInfoPlistURL),
             let versionHashes = versionInfo["NSManagedObjectModel_VersionHashes"] as? [String: AnyObject] else {
                 
-                fatalError("Could not load \(typeName(NSManagedObjectModel)) metadata from path \"\(versionInfoPlistURL)\"."
-                )
+                fatalError("Could not load \(typeName(NSManagedObjectModel)) metadata from path \"\(versionInfoPlistURL)\".")
         }
         
         let modelVersions = Set(versionHashes.keys)
         let currentModelVersion: String
-        if let modelVersion = modelVersion {
+        if let plistModelVersion = versionInfo["NSManagedObjectModel_CurrentVersionName"] as? String where modelVersionHints.isEmpty || modelVersionHints.contains(plistModelVersion) {
             
-            currentModelVersion = modelVersion
+            currentModelVersion = plistModelVersion
+        }
+        else if let resolvedVersion = modelVersions.intersect(modelVersionHints).first {
+            
+            CoreStore.log(
+                .Warning,
+                message: "The MigrationChain leaf versions do not include the model file's current version. Resolving to version \"\(resolvedVersion)\"."
+            )
+            currentModelVersion = resolvedVersion
+        }
+        else if let resolvedVersion = modelVersions.first ?? modelVersionHints.first {
+            
+            CoreStore.log(
+                .Warning,
+                message: "The MigrationChain leaf versions do not include any of the model file's embedded versions. Resolving to version \"\(resolvedVersion)\"."
+            )
+            currentModelVersion = resolvedVersion
         }
         else {
             
-            currentModelVersion = versionInfo["NSManagedObjectModel_CurrentVersionName"] as? String ?? modelVersions.first!
+            fatalError("No model files were found in URL \"\(modelFileURL)\".")
         }
         
         var modelVersionFileURL: NSURL?

CoreStore/Logging/DefaultLogger.swift

@@ -69,7 +69,7 @@ public final class DefaultLogger: CoreStoreLogger {
     public func handleError(error error: NSError, message: String, fileName: StaticString, lineNumber: Int, functionName: StaticString) {
         
         #if DEBUG
-            Swift.print("⚠️ [CoreStore: Error] \(fileName.stringValue.lastPathComponent):\(lineNumber) \(functionName)\n  ↪︎ \(message): \(error)\n")
+            Swift.print("⚠️ [CoreStore: Error] \(fileName.stringValue.lastPathComponent):\(lineNumber) \(functionName)\n  ↪︎ \(message)\n    \(error)\n")
         #endif
     }
     

CoreStore/Migrating/DataStack+Migration.swift

@@ -413,7 +413,7 @@ public extension DataStack {
         
         while let nextVersion = migrationChain.nextVersionFrom(currentVersion),
             let sourceModel = model[currentVersion],
-            let destinationModel = model[nextVersion] {
+            let destinationModel = model[nextVersion] where sourceModel != model {
                 
                 if let mappingModel = NSMappingModel(
                     fromBundles: mappingModelBundles,

CoreStore/Migrating/MigrationChain.swift

@@ -29,6 +29,37 @@ import CoreData
 
 // MARK: - MigrationChain
 
+/**
+A `MigrationChain` indicates the sequence of model versions to be used as the order for incremental migration. This is typically passed to the `DataStack` initializer and will be applied to all stores added to the `DataStack` with `addSQLiteStore(...)` and its variants.
+
+Initializing with empty values (either `nil`, `[]`, or `[:]`) signifies to use the .xcdatamodel's current version as the final version, and to disable incremental migrations:
+
+    let dataStack = DataStack(migrationChain: nil)
+
+This means that the mapping model will be computed from the store's version straight to the `DataStack`'s model version.
+To support incremental migrations, specify the linear order of versions:
+
+    let dataStack = DataStack(migrationChain: 
+        ["MyAppModel", "MyAppModelV2", "MyAppModelV3", "MyAppModelV4"])
+
+or for more complex migration paths, a version tree that maps the key-values to the source-destination versions:
+
+    let dataStack = DataStack(migrationChain: [
+        "MyAppModel": "MyAppModelV3",
+        "MyAppModelV2": "MyAppModelV4",
+        "MyAppModelV3": "MyAppModelV4"
+    ])
+
+This allows for different migration paths depending on the starting version. The example above resolves to the following paths:
+- MyAppModel-MyAppModelV3-MyAppModelV4
+- MyAppModelV2-MyAppModelV4
+- MyAppModelV3-MyAppModelV4
+
+The `MigrationChain` is validated when passed to the `DataStack` and unless it is empty, will raise an assertion if any of the following conditions are met:
+- a version appears twice in an array
+- a version appears twice as a key in a dictionary literal
+- a loop is found in any of the paths
+*/
 public struct MigrationChain: NilLiteralConvertible, StringLiteralConvertible, DictionaryLiteralConvertible, ArrayLiteralConvertible {
     
     // MARK: NilLiteralConvertible
@@ -96,10 +127,28 @@ public struct MigrationChain: NilLiteralConvertible, StringLiteralConvertible, D
             }.map { $1 }
         )
         
+        let isVersionAmbiguous = { (start: String) -> Bool in
+            
+            var checklist: Set<String> = [start]
+            var version = start
+            while let nextVersion = versionTree[version] where nextVersion != version {
+                
+                if checklist.contains(version) {
+                    
+                    return true
+                }
+                checklist.insert(nextVersion)
+                version = nextVersion
+            }
+            
+            return false
+        }
+        
         self.versionTree = versionTree
         self.rootVersions = Set(versionTree.keys).subtract(versionTree.values)
         self.leafVersions = leafVersions
         self.valid = valid
+            && Set(versionTree.keys).union(versionTree.values).filter { isVersionAmbiguous($0) }.count <= 0
     }
     
     

CoreStore/Observing/DataStack+Observing.swift

@@ -78,6 +78,10 @@ public extension DataStack {
             NSThread.isMainThread(),
             "Attempted to observe objects from \(typeName(self)) outside the main thread."
         )
+        CoreStore.assert(
+            fetchClauses.filter { $0 is OrderBy }.count > 0,
+            "A ListMonitor requires an OrderBy clause."
+        )
         
         return ListMonitor(
             dataStack: self,
@@ -114,6 +118,10 @@ public extension DataStack {
             NSThread.isMainThread(),
             "Attempted to observe objects from \(typeName(self)) outside the main thread."
         )
+        CoreStore.assert(
+            fetchClauses.filter { $0 is OrderBy }.count > 0,
+            "A ListMonitor requires an OrderBy clause."
+        )
         
         return ListMonitor(
             dataStack: self,

CoreStore/Observing/ListMonitor.swift

@@ -500,21 +500,9 @@ public final class ListMonitor<T: NSManagedObject> {
             self.sectionIndexTransformer = { $0 }
         }
         
-        
         fetchedResultsControllerDelegate.handler = self
         fetchedResultsControllerDelegate.fetchedResultsController = fetchedResultsController
-        
-        do {
-            
-            try fetchedResultsController.performFetch()
-        }
-        catch {
-            
-            CoreStore.handleError(
-                error as NSError,
-                "Failed to perform fetch on \(typeName(NSFetchedResultsController))."
-            )
-        }
+        try! fetchedResultsController.performFetch()
     }
     
     

CoreStore/Observing/ObjectMonitor.swift

@@ -202,19 +202,7 @@ public final class ObjectMonitor<T: NSManagedObject> {
         
         fetchedResultsControllerDelegate.handler = self
         fetchedResultsControllerDelegate.fetchedResultsController = fetchedResultsController
-        
-        
-        do {
-            
-            try fetchedResultsController.performFetch()
-        }
-        catch {
-            
-            CoreStore.handleError(
-                error as NSError,
-                "Failed to perform fetch for \(typeName(NSFetchedResultsController))."
-            )
-        }
+        try! fetchedResultsController.performFetch()
         
         self.lastCommittedAttributes = (self.object?.committedValuesForKeys(nil) as? [String: NSObject]) ?? [:]
     }

CoreStore/Saving and Processing/Into.swift

@@ -44,11 +44,6 @@ public struct Into<T: NSManagedObject> {
     
     // MARK: Public
     
-    internal static var defaultConfigurationName: String {
-        
-        return "PF_DEFAULT_CONFIGURATION_NAME"
-    }
-    
     /**
     Initializes an `Into` clause.
     Sample Usage:
@@ -139,6 +134,11 @@ public struct Into<T: NSManagedObject> {
     
     // MARK: Internal
     
+    internal static var defaultConfigurationName: String {
+        
+        return "PF_DEFAULT_CONFIGURATION_NAME"
+    }
+    
     internal let entityClass: AnyClass
     internal let configuration: String?
     internal let inferStoreIfPossible: Bool

CoreStore/Setting Up/DataStack.swift

@@ -49,7 +49,7 @@ public final class DataStack {
     
     - parameter modelName: the name of the (.xcdatamodeld) model file. If not specified, the application name will be used.
     - parameter bundle: an optional bundle to load models from. If not specified, the main bundle will be used.
-    - parameter migrationChain: the `MigrationChain` that indicates the heirarchy of the model's version names. If not specified, will default to a non-migrating data stack.
+    - parameter migrationChain: the `MigrationChain` that indicates the sequence of model versions to be used as the order for incremental migration. If not specified, will default to a non-migrating data stack.
     */
     public required init(modelName: String = applicationName, bundle: NSBundle = NSBundle.mainBundle(), migrationChain: MigrationChain = nil) {
         
@@ -61,7 +61,7 @@ public final class DataStack {
         let model = NSManagedObjectModel.fromBundle(
             bundle,
             modelName: modelName,
-            modelVersion: migrationChain.leafVersions.first
+            modelVersionHints: migrationChain.leafVersions
         )
         
         self.coordinator = NSPersistentStoreCoordinator(managedObjectModel: model)