Change the behavior of user manager to only update values that actually changed when editing users (part of #2229)

(This also removes an additional db roundtrip when updating per-db user privileges that previously was needed to differentiate between user actions „Only removing privileges from user“ and „Backtracking on adding privileges to user“. Since we now only update changed values and the latter one would be an empty changeset this is no longer needed)

Author: dmoagx

Source/SPUserManager.m

@@ -1156,27 +1156,23 @@ - (BOOL)grantDbPrivilegesWithPrivilege:(SPPrivilegesMO *)schemaPriv skippingRevo
 	NSString *dbName = [schemaPriv valueForKey:@"db"];
     dbName = [dbName stringByReplacingOccurrencesOfString:@"_" withString:@"\\_"];
 
-	NSString *statement = [NSString stringWithFormat:@"SELECT USER, HOST FROM mysql.db WHERE USER = %@ AND HOST = %@ AND DB = %@",
-									  [[schemaPriv valueForKeyPath:@"user.parent.user"] tickQuotedString],
-									  [[schemaPriv valueForKeyPath:@"user.host"] tickQuotedString],
-									  [dbName tickQuotedString]];
-	
-	NSArray *matchingUsers = [connection getAllRowsFromQuery:statement];	
+	NSArray *changedKeys = [[schemaPriv changedValues] allKeys];
 
 	for (NSString *key in [self privsSupportedByServer])
 	{
 		if (![key hasSuffix:@"_priv"]) continue;
 
+		//ignore anything that we didn't change
+		if (![changedKeys containsObject:key]) continue;
+		
 		NSString *privilege = [key stringByReplacingOccurrencesOfString:@"_priv" withString:@""];
 
 		NS_DURING
 			if ([[schemaPriv valueForKey:key] boolValue] == YES) {
 				[grantPrivileges addObject:[privilege replaceUnderscoreWithSpace]];
 			}
 			else {
-				if ([matchingUsers count] || [grantPrivileges count] > 0) {
-					[revokePrivileges addObject:[privilege replaceUnderscoreWithSpace]];
-				}
+				[revokePrivileges addObject:[privilege replaceUnderscoreWithSpace]];
 			}
 		NS_HANDLER
 		NS_ENDHANDLER
@@ -1236,10 +1232,15 @@ - (BOOL)grantPrivilegesToUser:(SPUserMO *)user skippingRevoke:(BOOL)skipRevoke
 		NSMutableArray *grantPrivileges = [NSMutableArray array];
 		NSMutableArray *revokePrivileges = [NSMutableArray array];
 
+		NSArray *changedKeys = [[user changedValues] allKeys];
+		
 		for (NSString *key in [self privsSupportedByServer])
 		{
 			if (![key hasSuffix:@"_priv"]) continue;
 
+			//ignore anything that we didn't change
+			if (![changedKeys containsObject:key]) continue;
+			
 			NSString *privilege = [key stringByReplacingOccurrencesOfString:@"_priv" withString:@""];
 
 			// Check the value of the priv and assign to grant or revoke query as appropriate; do this