Rename *LookupTable data structures to *Map.

Frameworks/RSDatabase/Related Objects/RelatedObjectsMap.swift

@@ -0,0 +1,47 @@
+//
+//  RelatedObjectsMap.swift
+//  RSDatabase
+//
+//  Created by Brent Simmons on 9/10/17.
+//  Copyright © 2017 Ranchero Software, LLC. All rights reserved.
+//
+
+import Foundation
+
+// Map objectID to [DatabaseObject] (related objects).
+
+public struct RelatedObjectsMap {
+	
+	private let dictionary: [String: [DatabaseObject]] // objectID: relatedObjects
+	
+	init(relatedObjects: relatedObjects, lookupTable: LookupTable) {
+		
+		var d = [String: [DatabaseObject]]()
+		
+		let relatedObjectsDictionary = relatedObjects.dictionary()
+		let objectIDs = lookupTable.objectIDs()
+		
+		for objectID in lookupTable.objectIDs() {
+			
+			if let relatedObjectIDs = lookupTable[objectID] {
+				let relatedObjects = relatedObjectIDs.flatMap{ relatedObjectsDictionary[$0] }
+				if !relatedObjects.isEmpty {
+					d[objectID] = relatedObjects
+				}
+			}
+		}
+		
+		self.dictionary = d
+	}
+	
+	public func objectIDs() -> Set<String> {
+		
+		return Set(dictionary.keys)
+	}
+	
+	public subscript(_ objectID: String) -> [DatabaseObject]? {
+		get {
+			return dictionary[objectID]
+		}
+	}
+}