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Andrew Pallant

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Caching Locally

Physical Link: Caching Locally


One of the applications I have been working recently is a windows based application. Most things that the user keys into the system results in a database hit validation. To cut back on this I have implemented classes that assist in caching to the user’s local system. Based on the user’s habits, it will cache what the user uses commonly.

I am using a datatable in this example, but you could use a dictionary object. Should you choose to use a dictionary object, you could use LINQ to query the object. You could also make the caching class an extension which could cut down on some code an make it a little cleaner.

At the end of the day, this is one example only of what could be done.

Class Example

public class CurrencyCodes
private static CurrencyCodes _instance; // Instance Of Self

private static DataTable dt = new DataTable("CurrencyCodes");

public static CurrencyCodes Instance
{
get
{
if (_instance == null)
{
_instance = new CurrencyCodes();
}
return _instance;
}
}

private CurrencyCodes()
{
dt.Columns.Add("CurrencyCode", typeof(String));
dt.Columns.Add("LastUpdated", typeof(DateTime));
}

public String Search(String value)
{
DataRow[] rows = dt.Select("CurrencyCode='" + value + "'");
if (rows.Count() == 1) return value;
return "";
}

public void Add(String value)
{
DataRow row = dt.NewRow();
row["CurrencyCode"] = value;
row["LastUpdated"] = DateTime.Now;
dt.Rows.Add(row);
}

public void ClearCache()
{
dt.Rows.Clear();
}

public void LoadCache(String xml)
{
StringReader theReader = new StringReader(xml);
dt.ReadXml(theReader);
}

public String SaveCache()
{
using (MemoryStream ms = new MemoryStream())
{
dt.WriteXml(ms);
ms.Position = 0;

StreamReader sr = new StreamReader(ms, System.Text.Encoding.UTF8);

return sr.ReadToEnd();
}
}
}

Calling the class

Directory.SetCurrentDirectory(Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments));
if (!Directory.Exists("YourSoftwareCache"))
{
Directory.CreateDirectory("YourSoftwareCache");
}

if (File.Exists("CurrencyCodes.XML"))
CurrencyCodes.Instance.LoadCache(File.ReadAllText("CurrencyCodes.XML"));

CachedCurrencyCodes cachedCurrencyCodes = CachedCurrencyCodes.Instance;
CurrencyCode = cachedCurrencyCodes.Search(Criteria);

Note Comments have been stripped to clean up the posting. Always Comment Your Code.

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Categories: C#, Caching


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