To continue on the topic of Velocity, I will explore versioning today.
As I showed previously, you can use DataCache.Add method to add an item to cache. This, of course, requires that this item’s key was not to be found in the cache already, or an exception will be thrown. This puts a damper on versioning, So, let’s look at a different method – Put.
You can use Put method to add/replace an item in cache. If a key already exists, the item will be replaced, otherwise it will be added.
// add an item to cache
CachablePerson person1 = new CachablePerson();
person1.FirstName = "Version1";
DataCacheItemVersion version1 = _defaultCache.Put("personwithversion", person1);
Now, I will explore versioning of items. In order to control versioning, I will use GetAndLock method to get an item from cache while locking it to ensure safe updates. I will update a property of an object I got from cache, then I will put it back into cache.
// get an item and lock it
CachablePerson temp = _defaultCache.GetAndLock("personwithversion", TimeSpan.FromSeconds(1), out handle, true) as CachablePerson;
/update an item
temp.FirstName = "Version2";
//put it back and get the new version
DataCacheItemVersion version2 = _defaultCache.PutAndUnlock("personwithversion", temp, handle);
Now I will version that versioning actually works by getting both initial and new items
// get initial item
CachablePerson ver1 = (CachablePerson)_defaultCache.Get("personwithversion");
// get the item with version 2
CachablePerson ver2 = (CachablePerson)_defaultCache.GetIfNewer("personwithversion", ref version1);
To proof that the process worked, I will output the results to a window or console. In my case ver1.FirstName is Version1 and ver2.FirstName is Version2 which is what is expected.
In this post I looked at the Put method that makes it easier to put items into cache without worrying if an item with the same key already exists. I also looked at the way to maintain many versioned items with the same key in cache in case versioning is important to the consuming application.
You can download the updated initial sample here.