This tutorial is brought to you by NetroStar, a website development company.
Storing data can significantly improve performance of your applications and it can make them more user friendly by for instance remembering their settings. Then in the second part I'll compare them and show you similarities and differences between them.
Cache
Caching in ASP.NET is a very useful feature. It allows you to build complex and sophisticated applications without worrying too much about performance issues. Basically it saves already rendered HTML of your website, controls or some other objects in memory and later when they are needed by client's browser they are downloaded directly from cache without a need to generate them again. If data requested by client actually is in cache then it's called a cache hit. The more cache hits the better because then your application simply works faster. The number of cache hits depends of course on the size of the memory and the implementation of caching.
In ASP.NET there are three types of caching:
- Page Level Caching - it's simply caching whole HTML code of generated page
- Fragment Caching - caching small fragments of your website like for example user controls
- Caching Data Objects - allows you to cache objects from your application such as a table for instance
Now I'll describe briefly all three kinds of caching:
Page Level Caching
In this type of caching we want to save whole web page. To do so in ASP.NET is very easy, all you have to do is to put the following directive in your code:
The parameters used in this directive are the following (both are required):
- Duration - it defines time in seconds for how long the page should be in cache
- VaryByParam - parameters for which the page should be cached separately, value "none" means that there will be one page cached for all parameters, value "*" means that for each parameter the page will be cached separately. Each parameter should be separated using semicolon character (;)
And that's all you have to do to cache the whole page. As you see it's quite easy but it can provide huge performance gains depending on the content of your page.
Fragment Caching
Instead of caching whole website there is also a possibility to cache only a fragment such as a control. Implementation is exactly the same as for caching the whole page. The only difference is that OutputCache directive should be placed within a given control.
While using caching for a user control you can also use parameter VaryByControl with value being the name of some user-control on your web page. Then different options of this control (like for example different choices in drop down list) will be cached separately.
Caching Data Object
You can also save data to cache simply by using cache object, it's working like the standard dictionary with key-pairs value. It's best to show this on an example. Take a look how to add some data to cache:
Retrieving data is equally simple:
Please note that firstly we have to check if data stored in cache still exists, it could have been deleted by client's browser.
Session
Session state is simply a dictionary with key-value pairs and you can read or write it whenever you need during duration of a session. Session is a time when one concrete user interacts with your web application. Session state unlike application state is separate for each user. Using session state is very easy, you can for example save data from a user control to it:
Then you can use this data in any other part of your application simply by referring to it like in the following example:
One of the biggest advantages of session state in ASP.NET is that they are process independent, that means that session state can be saved in separate process so other processes can't affect it. Another advantage is that it also can work without cookies enabled in client's browser.
If you want to learn more about types of sessions check out our previous tutorials.
Cookies
Cookies are small files saved on client's disc used to store data concerning a concrete user. It can for example contain some preferences that user have chosen before so later the same preferences can be applied instantly.
You should keep in mind that you don't have complete control over cookies. Some browsers may accept cookies smaller than some size or even they may not accept cookies at all. What's more user can always delete all cookies from their browser so you shouldn't rely on them.
To create a cookie we'll use HttpCookie class like in the following example:
And now take a look at code that will allow you to read your cookie:
Comparison between caching, sessions and cookies
You should already have an idea about differences between these techniques but I'll present here a short summary. Choosing the right method of storage is very easy and straightforward if you follow few basic rules:
When to use caching
Cache is shared between all users of a given web application, that's why you should not store there data concerning individual users. You should use it to store whole web pages, controls or complex objects to enhance performance of your application.
When to use session
Session state unlike cache is separate for each session so you should store there data concerning only current session. Each session is valid only for one user so data stored there can't be accessed by other user's application. You can treat it as a storage for user data. Session state can also be store externally (for example in the database).
When to use cookies
Cookies should be used to store only data concerning user. What's more this data should be persistent like for example login name or some setting from your web application.
Summary
In this tutorial I have described caching, session state and cookies and explained also how to use them. It can be very useful in web design. As you see in ASP.NET it's quite easy and does not require much work. After reading the last part of this article choosing which technique of storing data to use should not be a big deal for you.
This tutorial was brought to you by NetroStar, a Miami-based global web design company.