Rajat Saddi's List: LINQ

• LINQ is a codename for a project which is a set of extensions to the .NET  Framework that encompasses language-integrated query, set and transform  operations. It extends C# and VB with native language syntax for queries and  provides class libraries to take advantage of these capabilities, available only  in .NET Framework 3.5. For developers who write code that regularly access a  recordset, this means a lot. The fact that queries are usually expressed in a  specialized query language for different data sources makes it difficult for  developers to learn a query language for each data source or data format that  they must access. This is what LINQ is all about.
• It simplifies data access by providing a consistent model for working with data  across various kinds of sources and formats.

  • This is test
• Notice that by simply creating a project that targets the .NET Framework 3.5  automatically adds a using directive for the System.Linq  namespace as this is already a part of the System.Core assembly.
• These are obtaining the data source, creating the query and executing the  query.
• Any LINQ query consists of three distinct actions.
• A queryable type does not require special modification to serve as a LINQ data  source as long as it is already loaded in memory.
• If not, you would have to load it into memory so LINQ can query the objects.
• A query specifies information to retrieve from the data source. This is similar  to a SQL query which includes syntaxes like SELECT, FROM, WHERE, GROUP BY, etc.  Looking at the code above, you'll notice that its not like your typical SQL  statement as the FROM clause appeared before the SELECT clause. There are a  couple of reasons for this. One, it adheres to the programming concept of  declaring the variable before using it. Also, from the point of view of Visual  Studio, this makes it easy to provide the IntelliSense feature using the dot (.) notation as the variable has already  been declared and that the framework has already inferred the correct type to  the object.  This provides the appropriate properties and methods, making  it easy for the developers to write their code.

  • Reason for the LINQ sysntax
• The from
• The from clause specifies the data  source, in this case, the carNames  collection. The where clause applies  the filter, in this case, the list of all elements in the collection containing  the letter 'e'. The select clause specifies the type of the  returned elements.
• Simply defining the query variable does not return any data nor takes any  action.
• The actual execution of the query is when we iterate over the query variable.
• This concept is called deferred query  execution.
• The use of a foreach statement  iterates thru the query variable and execute it as well.
• Another way is to bind the collection to a data-bound control in either a web or  windows form control similar to how you would do it in previous versions of  Visual Studio - specifying the DataSource property of the control to be the  query variable and calling the DataBind() method.

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• XElement
• XElement class which represents an XML element