C# – Linq – how to connect to a database

.net-4.0clinq

I have created a database with Microsoft SQL Server Management Studio (Microsoft SQL Server 2008).
I've been searching around but either I don't understand it or can't find it, but how do I connect from within my project (Visual Studio 2010 Enterprise) so that I can send and receive data from the DB?
My database name is MyDB.

var database = new MyDB();

In Solution Explorer, right-click References, and then click Add Reference.

In the Add Reference dialog box, click .NET, click the System.Data.Linq assembly, and then click OK.

The assembly is added to the project.

Add the following directives at the top of Program.cs:

Best Answer

The easiest way to add the ability to have an app communicate with a SQL Server database is to use LINQ to SQL. Assuming you've already made a database connection in the Server Explorer pane, then:

Add a new item to the project and choose teh LINQ to SQL Classes template
Enter an appropriate name (default is DataClasses1.dbml) and click add. The name you choose will also be used to create the class name of the DataContext by appending "DataContext" to the name you choose (e.g., Test.dbml is the filename and TestDataContext will be the classname.)
Then, from the Server Explorer window, drag the tables that you want to use into the dbml file that you created in step 2.
Search the web for resources on using LinqToSQL (my suggestion is to start with ScottGu's blog at http://weblogs.asp.net/scottgu/archive/2007/05/19/using-linq-to-sql-part-1.aspx)

Caveat: While this is the arguably the simplest way to get quick connectivity to a database, there are others that will have better performance and/or features like nHibernate or Microsoft's Entity Framework as Coding Gorilla also suggested.

Related Solutions

C# – LINQ query on a DataTable

You can't query against the DataTable's Rows collection, since DataRowCollection doesn't implement IEnumerable<T>. You need to use the AsEnumerable() extension for DataTable. Like so:

var results = from myRow in myDataTable.AsEnumerable()
where myRow.Field<int>("RowNo") == 1
select myRow;

And as @Keith says, you'll need to add a reference to System.Data.DataSetExtensions

AsEnumerable() returns IEnumerable<DataRow>. If you need to convert IEnumerable<DataRow> to a DataTable, use the CopyToDataTable() extension.

Below is query with Lambda Expression,

var result = myDataTable
    .AsEnumerable()
    .Where(myRow => myRow.Field<int>("RowNo") == 1);

C# – How to cast int to enum

From an int:

YourEnum foo = (YourEnum)yourInt;

From a string:

YourEnum foo = (YourEnum) Enum.Parse(typeof(YourEnum), yourString);

// The foo.ToString().Contains(",") check is necessary for enumerations marked with an [Flags] attribute
if (!Enum.IsDefined(typeof(YourEnum), foo) && !foo.ToString().Contains(","))
{
    throw new InvalidOperationException($"{yourString} is not an underlying value of the YourEnum enumeration.")
}

Update:

From number you can also

YourEnum foo = (YourEnum)Enum.ToObject(typeof(YourEnum) , yourInt);

Best Answer

Related Solutions

C# – LINQ query on a DataTable

C# – How to cast int to enum

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