Querying data from Sql Server Compact database gets easier!
“LINQ” stands for .net Language INtegrated Query. LINQ-enabled languages can provide full type-safety and compile-time checking of query expressions, and development tools can provide full intellisense, debugging, and rich refactoring support when writing LINQ code.
What is LINQ to SQL?
LINQ to SQL provides a runtime infrastructure for managing relational data as objects (object relational mapping) without losing the ability to query. You can query the database using LINQ and also update, insert or delete from it. LINQ to SQL stays in the background tracking your changes automatically.
LINQ to SQL provides an easy way to integrate data validation and business logic rules into your data model. Best of all, LINQ to SQL applications are easy to get started. LINQ to SQL: .NET Language-Integrated Query for Relational Data is an informative article on the topic.
Note: LINQ to SQL was formerly called DLINQ.
The good news for SQL Compact developers is that from Visual Studio ‘Orcas’ Beta2, LINQ to SQL will support SQL Compact as an underlying database!
Creating your first LINQ to SQL application over SQL Server Compact:
· Run the Windows SDK tool Program Files\Microsoft SDKs\Windows\v6.0A\Bin\SqlMetal.exe against your favorite sdf file. This will generate a .cs file.
e.g. >Sqlmetal.exe Northwind.sdf /code: Northwind.cs
· Create a new project and add the SqlMetal generated file to it.
· In solution explorer, add a reference to System.Data.Linq.dll.
· Instantiate the class that derives from DataContext (e.g. Northwind class for Northwind.cs) using connection string.
· Start writing queries against the instance just created.
Note: We didn’t specify SQL Compact as the provider anywhere! It is determined at runtime (unless you choose to override the default as a SQLMetal command line option).
Here’s a sample program:
static void Main(string args)
string connectionstring = "...";
Northwind db = new Northwind(connectionstring);
db.Log = Console.Out; // This lets you see the SQL we generate easily
var q = from c in db.Customers
where c.City == "London"
foreach (Customer cust in q) Console.WriteLine(cust.ContactName);
Now that you have your first program running, the article LINQ to SQL: .NET Language-Integrated Query for Relational Data should help discover other features of LINQ to SQL – a comprehensive but concise piece of write up! There are also numerous good posts on writing LINQ applications. I’ll point you to some of my favorites at the end of this post.
Differences between LINQ to SQL for SQL Server and SQL Server Compact:
- Notice the command line tool I referred you to for generating the object-relational mapping. While SQL Server will have a nice designer to do the same thing, atleast till Orcas, SQL Compact will have to do with SqlMetal command line tool. No designer support. (If you prefer command line tools like me, you shall have no problem!)
- Note: SQLMetal extracts SQL metadata from your database and generates a source file containing entity class declarations. Alternatively, you can split the process into two steps, first generating an XML file representing the SQL metadata and then later translating that XML file into a source file containing declarations. This split process allows you to retain the metadata as a file so you may edit it.
- LINQ queries are eventually mapped to SQL queries. Since SQL supported by SQL Server Compact is a strict subset of that on SQL Server, LINQ follows suit. (To see the SQL which is generated, set db.Log = Console.Out where db is the DataContext.).
- Stored procedures and views are not supported by SQL Server Compact, and so will not be supported through LINQ to SQL either.
Here are some of my favorite LINQ/ LINQ to SQL resources:
- LINQ to SQL: .NET Language-Integrated Query for Relational Data on MSDN.
- Overview of LINQ on MSDN
- ScottGu’s blogs