From 2cb74a032dc089ff86fd5fe7353db91721a85fbe Mon Sep 17 00:00:00 2001
From: Raadad Elsleiman <raadad@gmail.com>
Date: Tue, 6 Jan 2015 13:02:44 +1100
Subject: [PATCH] get and pass up feature to update higher caches

---
 lib/multi_caching.js       | 24 ++++++++++++++++++
 test/multi_caching.unit.js | 52 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 76 insertions(+)

diff --git a/lib/multi_caching.js b/lib/multi_caching.js
index 2dc52e7..4cb4b77 100644
--- a/lib/multi_caching.js
+++ b/lib/multi_caching.js
@@ -31,6 +31,30 @@ var multi_caching = function (caches) {
         }, cb);
     }
 
+     /**
+     * Looks for an item in cache tiers.
+     *
+     * When a key is found in a lower cache, all higher levels are updated
+     */
+
+    self.get_and_pass_up = function(key, cb) {
+        get_from_highest_priority_cache(key, function(err, result, index) {
+            if (err) {
+                return cb(err);
+            }
+
+            result = result || {};
+            cb(err, result);
+
+            if (result && index) {
+                var cachesToUpdate = caches.slice(0, index);
+                async.forEach(cachesToUpdate, function(cache, async_cb) {
+                    cache.set(key, result, result.ttl, async_cb);
+                });
+            }
+        });
+    };
+
     /**
      * Wraps a function in one or more caches.
      * Has same API as regular caching module.
diff --git a/test/multi_caching.unit.js b/test/multi_caching.unit.js
index 746c951..37ba211 100644
--- a/test/multi_caching.unit.js
+++ b/test/multi_caching.unit.js
@@ -178,6 +178,58 @@ describe("multi_caching", function () {
         });
     });
 
+    describe("get_and_pass_up()", function () {
+        var value;
+        var key;
+
+        describe("using a single cache store", function () {
+            beforeEach(function () {
+                multi_cache = multi_caching([memory_cache3]);
+                key = support.random.string(20);
+                value = support.random.string();
+            });
+
+            it("gets data from first cache that has it", function (done) {
+                memory_cache3.set(key, value, ttl, function (err) {
+                    check_err(err);
+
+                    multi_cache.get_and_pass_up(key, function (err, result) {
+                        check_err(err);
+                        assert.equal(result, value);
+                        done();
+                    });
+                });
+            });
+        });
+
+        describe("using multi cache store", function () {
+            beforeEach(function () {
+                multi_cache = multi_caching([memory_cache,memory_cache2,memory_cache3]);
+                key = support.random.string(20);
+                value = support.random.string();
+            });
+
+            it("checks to see if higher levels have item", function (done) {
+                memory_cache3.set(key, value, ttl, function (err) {
+                    check_err(err);
+
+                    multi_cache.get_and_pass_up(key, function (err, result) {
+                        check_err(err);
+                        assert.equal(result, value);
+
+                        process.nextTick(function() {
+                            memory_cache.get(key, function (err, result) {
+                                assert.equal(result, value);
+                                check_err(err);
+                                done();
+                            });
+                        });
+                    });
+                });
+            });
+        });
+    });
+
     describe("wrap()", function () {
         describe("using a single cache store", function () {
             beforeEach(function () {