Sharepoint Coding Best Practices [MSDN]

This post is straight away from MSDN, but reason being, i found it very interesting and usefull while tuning the performance or while developing custom development projects.

Using SharePoint Data and Objects Efficiently

Caching Data and Objects

 Many developers use the Microsoft .NET Framework caching objects (for example, System.Web.Caching.Cache) to help take better advantage of memory and increase overall system performance. But many objects are not "thread safe" and caching those objects can cause applications to fail and unexpected or unrelated user errors.

Caching SharePoint Objects That Are Not Thread Safe

You might try to increase performance and memory usage by caching SPListItemCollection objects that are returned from queries. In general, this is a good practice; however, the SPListItemCollection object contains an embedded SPWeb object that is not thread safe and should not be cached.

Understanding the Potential Pitfalls of Thread Synchronization

You might not be aware that your code is running in a multithreaded environment (by default, Internet Information Services, or IIS, is multithreaded) or how to manage that environment. The following example shows the code some developers use to cache Microsoft.SharePoint.SPListItemCollection objects.

Bad Practice:

public void CacheData()
{
   SPListItemCollection oListItems;

   oListItems = (SPListItemCollection)Cache["ListItemCacheName"];
   if(oListItems == null)
   {
      oListItems = DoQueryToReturnItems();
      Cache.Add("ListItemCacheName", oListItems, ..);
   }
}

If the query in the preceding example takes 10 seconds to complete, many users could try to access that page simultaneously during that amount of time. In this case, all of the users would run the same query, which would attempt to update the same cache object. If that same query runs 10, 50, or 100 times, with multiple threads trying to update the same object at the same time—especially on multiprocess, hyperthreaded computers—performance problems would become especially severe.

Good Practice: Locking

private static object _lock =  new object();

public void CacheData()
{
   SPListItemCollection oListItems;

   lock(_lock) 
   {
      oListItems = (SPListItemCollection)Cache["ListItemCacheName"];
      if(oListItems == null)
      {
         oListItems = DoQueryToReturnItems();
         Cache.Add("ListItemCacheName", oListItems, ..);
     }
   }
}

Better Practice:

private static object _lock =  new object();

public void CacheData()
{
   SPListItemCollection oListItems;
       oListItems = (SPListItemCollection)Cache["ListItemCacheName"];
      if(oListItems == null)
      {
         lock (_lock) 
         {
              //Ensure that the data was not loaded by a concurrent thread while waiting for lock.
              oListItems = (SPListItemCollection)Cache[“ListItemCacheName”];
              if (oListItems == null)
              {
                   oListItems = DoQueryToReturnItems();
                   Cache.Add("ListItemCacheName", oListItems, ..);
              }
         }
     }
}

Using Objects in Event Receivers 
 Do not instantiate SPWeb, SPSite, SPList, or SPListItem objects within an event receiver. Event receivers that instantiate SPSite, SPWeb, SPList, or SPListItem objects instead of using the instances passed via the event properties can cause the following problems:

• They incur significant additional roundtrips to the database. (One write operation can result in up to five additional roundtrips in each event receiver.)
  
  
• Calling the Update method on these instances can cause subsequent Update calls in other registered event receivers to fail.

Bad Practice:

public override void ItemDeleting(SPItemEventProperties properties)
{
    using (SPSite site = new SPSite(properties.WebUrl))

    using (SPWeb web = site.OpenWeb())
        {
        SPList list = web.Lists[properties.ListId];
        SPListItem item = list.GetItemByUniqueId(properties.ListItemId);
        // Operate on item.
        }
    }
}

Good Practice:

// Retrieve SPWeb and SPListItem from SPItemEventProperties instead of
// from a new instance of SPSite.
SPWeb web = properties.OpenWeb();
// Operate on SPWeb object.
SPListItem item = properties.ListItem;
// Operate on item.

Working with Folders and Lists
When folders and lists grow in size, custom code that works with them needs to be designed in ways that optimize performance. Otherwise, your applications will run slowly and even cause timeouts to occur.

Do not use SPList.Items

Use SPList.GetItems(SPQuery query) instead. Apply filters, if appropriate, and specify only the fields you need to make the query more efficient. If the list contains more than 2,000 items, you will need to paginate the list in increments of no more than 2,000 items. The following code example shows how to paginate a large list.

Good Practice: using SPList.GetItems() 

SPQuery query = new SPQuery();
SPListItemCollection spListItems ; 
string lastItemIdOnPage = null; // Page position.
int itemCount = 2000
 
while (itemCount == 2000)
{
    // Include only the fields you will use.
    query.ViewFields = "";   
    query.RowLimit = 2000; // Only select the top 2000.
    // Include items in subfolder (if necessary).
    query.ViewAttributes = "Scope=\"Recursive\"";
    StringBuilder sb = new StringBuilder();
    // To make it order by ID and stop scanning the table, specify the OrderBy override attribute.
    sb.Append("");
    //.. Append more text as necessary ..
    query.Query = sb.ToString();
    // Get 2,000 more items.
 
    SPListItemCollectionPosition pos = new SPListItemCollectionPosition(lastItemIdOnPage);
    query.ListItemCollectionPosition = pos; //page info
    spListItems = spList.GetItems(query);
    lastItemIdOnPage = spListItems.ListItemCollectionPosition.PagingInfo;
    // Code to enumerate the spListItems.
    // If itemCount <2000, we finish the enumeration.
    itemCount = spListItems.Count;

}

Paginating Large Lists Using SPList.GetItems()

SPWeb oWebsite = SPContext.Current.Web;
SPList oList = oWebsite.Lists["Announcements"];

SPQuery oQuery = new SPQuery();
oQuery.RowLimit = 10;
int intIndex = 1;

do
{
    Response.Write("
Page: " + intIndex + "
");
    SPListItemCollection collListItems = oList.GetItems(oQuery);

    foreach (SPListItem oListItem in collListItems)
    {
        Response.Write(SPEncode.HtmlEncode(oListItem["Title"].ToString()) +"
");
    }

    oQuery.ListItemCollectionPosition = collListItems.ListItemCollectionPosition;
    intIndex++;
} while (oQuery.ListItemCollectionPosition != null);

Getting items by identifier

Instead of using SPList.Items.GetItemById, use SPList.GetItemById(int id, string field1, params string[] fields). Specify the item identifier and the field that you want.

Do not enumerate entire SPList.Items collections or SPFolder.Files collections

Accessing the methods and properties that are listed in the left column of the following table will enumerate the entire SPList.Items collection, and cause poor performance and throttling for large lists. Instead, use the alternatives listed in the right column.

Whenever possible, acquire a reference to a list by using the list's GUID or URL as a key.

You can retrieve an SPList object from the SPWeb.Lists property by using the list's GUID or display name as an indexer. Using SPWeb.Lists[GUID] and SPWeb.GetList(strURL) is always preferable to using SPWeb.Lists[strDisplayName]. Using the GUID is preferable because it is unique, permanent, and requires only a single database lookup. The display name indexer retrieves the names of all the lists in the site and then does a string comparison with them. If you have a list URL instead of a GUID, you can use the GetList method to look up the list's GUID in the content database before retrieving the list. 

Deleting Multiple Versions of a List Item
When you delete multiple versions of a list item, use the DeleteByID method; do not use the Delete method. You will experience performance problems if you delete each SPListItemVersion object from an SPListItemVersionCollection object. The recommended practice is to create an array that contains the ID properties of each version and then delete each version by using the SPFileVersionCollection.DeleteByID method. The following code examples demonstrate both the approach that is not recommended and the recommended approach to deleting all versions of the first item of a custom list.

Bad Practice:

SPSite site = new SPSite("site url");
SPWeb web = site.OpenWeb();
SPList list = web.Lists["custom list name"];
SPListItem item = list.GetItemById(1); 
SPListItemVersionCollection vCollection = item.Versions;
ArrayList idList = new ArrayList();
foreach(SPListItemVersion ver in vCollection)
{
  idList.Add(ver.VersionId);
}
foreach(int verID in idList)
{
  SPListItemVersion version = vCollection.GetVersionFromID(verID); 
try
{
  version.Delete();
}
catch (Exception ex)
{
  MessageBox.Show(ex.Message);  
}
}

Good Practice:Deleting each version of a list item by using the SPFileVersionCollection.DeleteByID method

SPSite site = new SPSite("site url");
SPWeb web = site.OpenWeb();
SPList list = web.Lists["custom list name"];
SPListItem item = list.GetItemById(1);
SPFile file = web.GetFile(item.Url);
SPFileVersionCollection collection = file.Versions;
ArrayList idList = new ArrayList();
foreach (SPFileVersion ver in collection)
{
  idList.Add(ver.ID);
}
foreach (int verID in idList)
{
try
{
  collection.DeleteByID(verID);
}
catch (Exception ex)
{
  MessageBox.Show(ex.Message);  
}
}

If you are deleting versions of items in a document library, you can use a similar approach by retrieving the SPListItem.File.Versions property, as in the following code example.
Good Coding Practice: Deleting each version of a list item in a document library by using the SPFileVersionCollection.DeleteByID method

SPSite site = new SPSite("site url");
SPWeb web = site.OpenWeb();
SPList list = web.Lists["custom list name"];
SPFile file = list.RootFolder.Files[0];
SPFileVersionCollection collection = file.Versions;

ArrayList idList = new ArrayList();
foreach (SPFileVersion ver in collection)
{
  idList.Add(ver.ID);
}
foreach (int verID in idList)
{
try
{
  collection.DeleteByID(verID);
}
catch (Exception ex)
{
  MessageBox.Show(ex.Message);  
}
}

Using SPQuery Objects

SPQuery objects can cause performance problems whenever they return large result sets. The following suggestions will help you optimize your code so that performance will not suffer greatly whenever your searches return large numbers of items.

• Do not use an unbounded SPQuery object.
  
  An SPQuery object without a value for RowLimit will perform poorly and fail on large lists. Specify a RowLimit between 1 and 2000 and, if necessary, page through the list.
  
  
• Use indexed fields.
  
  If you query on a field that is not indexed, the query will be blocked whenever it would result in a scan of more items than the query threshold (as soon as there are more items in the list than are specified in the query threshold). Set SPQuery.RowLimit to a value that is less than the query threshold.
  
  
• If you know the URL of your list item and want to query by FileRef, use SPWeb.GetListItem(string strUrl, string field1, params string[] fields) instead.
  
  

Using Web Controls

When you inherit and override controls in the Microsoft.SharePoint.WebControls namespace, remember that SharePoint Web controls are templated controls. Unlike Microsoft ASP.NET Web controls, they are defined and rendered with templates instead of with the CreateChildControls method. Instead of having a thick CreateChildControls method that uses the new operator to create child controls, perform most child control creation and rendering by using the rendering templates that are referenced in the Template, AlternateTemplate, DisplayTemplate, CustomTemplate, and AlternateCustomTemplate properties of the SharePoint Web control. SharePoint Web controls do inherit the CreateChildControls method, but that method should typically do little or nothing beyond calling the parent control's CreateChildControls method and perhaps a bit of "final polish" rendering, such as assigning default values to child control properties in New mode or assigning the current values in Edit mode.

Creating Timer Jobs

Design your timer jobs so that they consist of small, manageable pieces. Because administrators and other events, such as system restarts, can stop timer jobs, you can minimize the amount of rework after any interruption by breaking timer jobs into small pieces of work.

If you consider these issues when you write your code, your SharePoint system will run more efficiently and your users will have a much better experience. You can also help to prevent unexpected failures and errors in your system.

Is it helpful for you? Kindly let me know your comments / Questions.