LINQ
Providers
1.
LINQ to Objects
2.
LINQ to XML (XLINQ)
3.
LINQ to SQL (DLINQ)
4.
LINQ to DataSets
5.
LINQ to Entities
![LINQ.jpg]()
LINQ
to Objects
LINQ
to Objects allows .NET developers to write “queries” over collections of
objects.The code generated by this provider refers to the implementation of the
standard query operators as defined on the Sequence pattern and allows IEnumerable<T> collections to be
queried locally.
In
a basic sense, LINQ to Objects represents a new approach to collections. In the
old way, you had to write complex for each loops that specified how to retrieve
data from a collection. In the LINQ approach, you write declarative
code that describes what you want to retrieve.
Following
is an example which takes the first four integers from the collection
(using LINQ)-
IEnumerable<int>
firstFourNumbers = integers.Take(4);
Console.WriteLine("First 4 numbers:");
foreach (var
num in firstFourNumbers)
{
Console.WriteLine(num);
}
LINQ to XML (XLINQ)
The LINQ to XML provider converts
an XML document to a collection of XElement objects, which are then queried
against using the local execution engine
that is provided as a
part of the implementation of the standard query operator.
LINQ to XML allows us to
create, read and edit XML files and what's more important is that it is done in
a very easy and understandable way. To use LINQ
to XML you should add a
reference to the System.Xml.Linq.dll (for the XDocument and the other classes)
and use the System.Linq namespace (for the LINQ syntax).
LINQ to SQL (DLINQ)
LINQ to SQL provides a
runtime infrastructure for managing relational data as objects without losing
the ability to query. Your application is free to manipulate
the objects while LINQ to
SQL stays in the background tracking your changes automatically.
LINQ to SQL does not use
the query engine of LINQ. Instead, it converts a LINQ query to a SQL query that
is then sent to SQL Server for
processing.
The mapping is done by
defining classes that correspond to the tables in the database.
Example-
[Table(Name="Customers")]
public class Customer
{
[Column(IsPrimaryKey = true)]
public int CustID;
[Column]
public string CustName;
}
LINQ to DataSets
LINQ to DataSet makes it
easier and faster to query over data cached in a DataSet object. Specifically,
LINQ to DataSet simplifies querying by enabling
developers to write
queries from the programming language itself, instead of by
using a separate query language
LINQ to DataSet allows us
to make use of the new superior LINQ querying features in legacy applications
without having to rewrite the whole data access
layer.
LINQ to Entities
LINQ
to Entities provides Language-Integrated Query (LINQ) support that enables
developers to write queries against the Entity Framework conceptual model using
Visual Basic or Visual C#. Queries against the Entity Framework are represented
by command tree queries, which execute against the object context. LINQ to
Entities converts Language-Integrated Queries (LINQ) queries to command tree
queries, executes the queries against the Entity Framework, and returns objects
that can be used by both the Entity Framework and LINQ. The following is the
process for creating and executing a LINQ to Entities query:
- Construct an
ObjectQuery instance from ObjectContext.
- Compose a LINQ
to Entities query in C# or Visual Basic by using the ObjectQuery
instance.
- Convert LINQ
standard query operators and expressions to command trees.
- Execute the
query, in command tree representation, against the data source. Any
exceptions thrown on the data source during execution are passed directly
up to the client.
- Return query
results back to the client.