Sunday, September 29, 2013

SharePoint 2013 - Coding standards and best practices

In this post we will go through some of the coding standards and best practices that have been recommended by Microsoft for SharePoint 2013.

Using SharePoint Data and Objects Efficiently
Caching is one good way to improve system performance. However, you must weigh the benefits of caching against the need for thread safety. Additionally, you should not create certain SharePoint objects within event receivers because this will cause performance problems related to excessive database calls.

1) 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.

2) 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. For example, assume the SPListItemCollection object is cached in a thread. As other threads try to read this object, the application can fail or behave strangely because the embedded SPWeb object is not thread safe. For more information about the SPWeb object and thread safety, see the Microsoft.SharePoint.SPWeb class. The guidance in the following section describes how you can prevent multiple threads from attempting to read the same cached object.

3) 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 Coding Practice
Caching an Object That Multiple Threads Might Read
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.
}
}
}

Applying a Lock
Checking for null
// 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. The following recommendations for addressing performance concerns while working with large folders and lists are based on the test results reported in Steve Peschka's white paper, Working with Large Lists in Office SharePoint Server 2007.

1)  Do not use SPList.Items.SPList.Items 
Selects all items from all subfolders, including all fields in the list. Use the following alternatives for each use case.
Retrieving all items in a list 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. 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.

2) 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.

3) 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] andSPWeb.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.

4) Avoid creating and destroying objects unnecessarily in code
Avoid creating and destroying objects unnecessarily in code, as this may require that extra queries be made against the database and may even involve code that is incorrect.
In the following example, separate objects for the Tasks list must be instantiated each time the indexer is used to set properties and the method for updating is called. This is not a recommended practice.

Bad Practice
SPWeb myWeb = SPContext.Current.Web; 
myWeb.Lists["Tasks"].Title = "List_Title"; 
myWeb.Lists["Tasks"].Description = "List_Description"; 
myWeb.Lists["Tasks"].Update(); 

Good Practice
SPWeb myWeb = SPContext.Current.Web; 
SPList myList = myWeb.Lists["Tasks"]; 
myList.Title="List_Title"; 
myList.Description="List_Description"; 
myList.Update();

Note: 
a) The object models in the Microsoft.SharePoint assembly optimize performance and minimize the number of SQL queries that are made. However, to monitor code performance, it is recommended that you use the SQL Profiler.
b) To return a single item from a collection, always use a Get* method when one is provided through a parent object, instead of iterating through the entire collection and using an indexer. 

5) Handling large folders and lists
When the size of folders and lists increases, you must design custom code that works with them to optimize performance. Otherwise, your applications will run slowly and can cause service or page load timeouts. The two primary areas for concern when handling large folders and lists are the following:
Query throttling, which can cause the behavior of your code to change in unexpected and unpredictable ways over time as your site evolves and your queries begin to return items that exceed the query threshold.
Efficient retrieval of items from large folders and lists.

6) Throttling for Large List Queries
Microsoft SharePoint Foundation 2013 and Microsoft SharePoint Server 2013 apply a default query threshold of 5,000 items. Any custom code that relies on query result sets that can exceed this maximum will not perform as expected. Queries on lists consisting of more than 5,000 items that include fields that are not indexed in their query conditions will also fail, because those queries must scan all rows in a list. Follow the steps listed below to view and increase this limit or to enable the object model to override the limit:
To view and increase this threshold or to enable the object model to override the threshold
On the Central Administration site, under Application Management, click Manage Web Applications.
Click General Settings, and then click Resource Throttling.
View and update the threshold or allow the object model to override the limit.

7) 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 eachSPListItemVersion 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 Coding Practice
Deleting each SPListItemVersion object
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 Coding 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); 
}

8) 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 thickCreateChildControls 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 CreateChildControlsmethod 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.

Avoiding Unnecessary Construction of SPWeb and SPSite Objects
An SPWeb or SPSite object can occupy a lot of memory. Avoid constructing objects of these types simply to get a reference to a parent object. Instead, to get a reference to a web application, use the static SPWebApplication.Lookup(Uri) method, and pass it a Uri object that is created with the URI of the web application. You can then get a reference to the farm by using the Farm property of the web application object. (You can get a reference to a remote farm by using the static Open(String) method.) TheContentDatabases property of the web application object contains a collection of the content databases in the web application. You can get a reference to a particular content database through this property if you know its index in the collection. For more information, see the reference topic for the SPContentDatabaseCollection class. The following code illustrates some of these points.
SPWebApplication webApplication = SPWebApplication.Lookup(new Uri("http://localhost/"); 
SPFarm farm = webApplication.Farm
SPContentDatabase content = webApplication.ContentDatabases[0];

File Naming Restrictions 
For security reasons, SharePoint Foundation reads files in the %ProgramFiles%\Common Files\Microsoft Shared\web server extensions\15\TEMPLATE directory tree only if their names are composed of ASCII letters, numbers, periods, underscores, or dashes. In addition, file names cannot contain two or more consecutive periods. For example:
Following are permitted file names:
a) AllItems.aspx
b) Dept_1234.doc
c) Long.Name.With.Dots.txt
The following are not permitted file names:
a) Cæsar.wav
b) File Name With Spaces.avi
c) Wow...ThisIsBad.rtf
d) 揵.htm

Accessing Web and Site Objects

1) Get Current Site details using SPSite 
 SPSite oSiteCollection = SPContext.Current.Site;

2) Get Current Web details using SPWeb 
 SPWeb oWebSite = SPContext.Current.Web;

3) When your code is contained in an .aspx file or the "code behind" in an .aspx.cs file, you can use methods to get the SPWeb.
SPWeb oWebSite = SPControl.GetContextWeb(Context);  where Context = System.Web.UI.Page.Context

4) To get reference of the current web object from .aspx page that is inherited from LayoutsPageBase is :
SPWeb oWebSite = this.Web;

5) Use the Microsoft.SharePoint.SPSite.AllWebs property to obtain a reference to a Web site other than the current one. 
SPWeb oWebSite = SPContext.Current.Site.AllWebs["myOtherSite"];

6) Get reference of server farm or current physical server : 
SPFarm oFarm = SPFarm.Local;


Access external systems
When the data source is a Web service or database, consider using the Business Data Catalog (BDC) for SP 2007 and Business Connectivity Services (BCS) for SP 2013.
SharePoint Databases
Do not make calls directly to the SharePoint content and configuration databases.
Packaging
Structure your code project so that solution packaging is integrated into the project

Dispose Objects
We should not dispose any SPWeb, SPSite object create using SPContext.Current.Site, SPContext.Current.Web, SPControl.GetContextWeb(Context), this.Web
We should explicitly dispose of references to objects obtained through the AllWebs property
The code should dispose any SPSite or SPWeb object obtained by using a constructor.
Do not dispose dispose of the SPWeb.ParentWeb
The SPWeb.Webs property returns an SPWebCollection object. The SPWeb objects in this collection must be disposed.
The SPWeb.Webs.Add method (or Add) creates and returns a new SPWeb object. You should dispose of any SPWeb object returned from this method call.
If the object is obtained from the SharePoint context objects (GetContextSite method and GetContextWeb method), the calling application should not call the Dispose method on the object.
You should still dispose of an object that is created from these objects, for example, if a Web site is opened from an SPSite object that you obtained by using the GetContextSite method.

Wrong Way
void CombiningCallsLeak()
{
    using (SPWeb web = new SPSite(SPContext.Current.Web.Url).OpenWeb())
    {
        // ... New SPSite will be leaked.
    } // SPWeb object web.Dispose() automatically called.
}

Right Way
void CombiningCallsBestPractice()
{
    using (SPSite siteCollection = new SPSite(SPContext.Current.Web.Url))
    {
        using (SPWeb web = siteCollection.OpenWeb())
        {
        //Perform operations on site.
        } // SPWeb object web.Dispose() automatically called.
    }  // SPSite object siteCollection.Dispose() automatically called.
}

Exception Handling in SharePoint

1. Avoid empty Catch blocks
All the errors should be reported using error logging functionality, if not handled sufficiently.
Wrong Way
try
{
    // code
}
catch { }

2. Use throw; if you’re going to throw an exception
Wrong Way
try
{
    // code
}
catch (Exception ex)
{
    throw ex;
}

Right Way
try
{
    // code
}
catch
{
    throw;
}

3. Handle the specific exception wherever possible
Right Way
try
{
    spList = spWeb.GetList("/Path/List");
}
catch (FileNotFoundException ex)
{
    // handle exception
}
catch (ArgumentException ex)
{
    // handle exception
}

4. Try to check condition before it throws exception
Wrong Way
try
{
    myString = listItem["MyField"].ToString();
}
catch (Exception ex)
{
    // handle exception
}
Right Way
if (String.IsNullOrEmpty(listItem["MyField"]))
{
    myString = listItem["MyField"].ToString();
}

6. Use an appropriate form of logging exception.
 The most important takeaway is to ensure that the errors are logged. The 2 most logical locations to log the errors would be the ULS or Event Log, however this may not always be appropriate. If these locations aren’t regularly monitored or accessible by the people who need to know about the errors, then it is essentially no better than swallowing the errors in the first place. Email, CRM, a database or even a SharePoint list are other potential locations that could be more accessible. Logging to a file on the file system makes little sense seeing if that is an accessible option you could just use the ULS.

7. Use a custom error page.
Nothing looks worse on a public facing internet site or even an intranet application than when you get the SharePoint default error page. Wherever possible you should display a user friendly message rather than an ugly generic error page.

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