LINQ to Objects
LINQ to ADO.NET -|-LINQ to SQL
|-LINQ to DataSet
|-LINQ to Entiries
LINQ to XML
(SOAP)Simple Object Access Protocol
LINQ to Object
LINQ query that gets temporary files greater than 10,000 bytes, ordered by size
string tempPath = Path.GetTempPath();
DirectoryInfo dirInfo = new DirectoryInfo( tempPath );
var query =
from f in dirInfo.GetFiles()
where f.Length > 10000
orderby f.Length descending
select f;
LINQ to ADO.NET
LINQ to ADO.NET includes different LINQ implementations that share the need to manipulate
relational data. It includes other technologies that are specific to each particular persistence layer:
■ LINQ to SQL Handles the mapping between custom types in C# and the physical table
schema.
■ LINQ to Entities Is in many ways similar to LINQ to SQL. However, instead of using the
physical database as a persistence layer, it uses a conceptual Entity Data Model (EDM).
The result is an abstraction layer that is independent from the physical data layer.
■ LINQ to DataSet Makes it possible to query a DataSet using LINQ.
LINQ to SQL and LINQ to Entities have similarities because they both access information
stored in a relational database and operate on object entities that represent external data in
memory. The main difference is that they operate at a different level of abstraction. While
LINQ to SQL is tied to the physical database structure, LINQ to Entities operates over a con-
ceptual model (business entities) that might be far from the physical structure (database
tables).
The reason for these different options for accessing relational data through LINQ is that
different models for database access are in use today. Some organizations implement all access
through stored procedures, including any kind of database query, without using dynamic
queries. Many others use stored procedures to insert, update, or delete data and dynamically
built SELECT statements to query data. Some see the database as a simple object persistence
layer, while others put some business logic into the database using triggers, stored proce-
dures, or both. LINQ tries to offer help and improvements in database access without forcing
everyone to adopt a single comprehensive model.
LINQ to XML
LINQ to XML offers a slightly different syntax that operates on XML data, allowing query and
data manipulation. A particular type of support for LINQ to XML is offered by Visual Basic
9.0, which includes XML literals in the language. This enhanced support simplifies the code
necessary to manipulate XML data. In fact, you can write such a query in Visual Basic 9.0:
Dim book = _
<Book Title="Introducing LINQ">
<%= From person In team _
Where person.Role = "Author" _
Select <Author><%= person.Name %></Author> %>
</Book>
This query corresponds to the following C# 3.0 syntax:
dim book =
new XElement( "Book",
new XAttribute( "Title", "Introducing LINQ" ),
from person in team
where person.Role == "Author"
select new XElement( "Author", person.Name ) );