New nested-transaction method

Author: marcoarment

FCModel/FCModel.h

@@ -189,6 +189,9 @@ typedef NS_ENUM(NSInteger, FCModelChangeType) {
 + (void)performTransaction:(BOOL (^)(void))block; // return YES to commit, NO to roll back
 + (BOOL)isInTransaction;
 
+// This variant has no control over commit/rollback; safe to potentially nest inside other transactions if you only want performance
++ (void)performInTransactionForPerformance:(void (^)(void))block;
+
 // Field info: You probably won't need this most of the time, but it's nice to have sometimes. FCModel's generating this privately
 //  anyway, so you might as well have read-only access to it if it can help you avoid some code. (I've already needed it.)
 //

FCModel/FCModel.m

@@ -1117,6 +1117,14 @@ + (BOOL)isInTransaction
     return inTransaction;
 }
 
++ (void)performInTransactionForPerformance:(void (^)(void))block
+{
+    [self inDatabaseSync:^(FMDatabase *db) {
+        if (db.inTransaction) block();
+        else [self performTransaction:^BOOL{ block(); return YES; }];
+    }];
+}
+
 + (void)performTransaction:(BOOL (^)(void))block
 {
     __block NSDictionary *changedFieldsToNotify = nil;