Skip to main content

Basics of LINQ

LINQ
It stands for Language Integrated Query. By using LINQ we can query database using statements that are built into LINQ-enabled languages such as MS C# and VB 2010.
LINQ works with any collection that implements the IEnumerable or the generic IEnumerable<T> interface. The generic IEnumerable interface has only one method, GetEnumerator, that returns an object that implements the generic IEnumertaor interface. The generic IEnumertaor interface has a Current property, which references the current item in the collection, and two methods, MoveNext and Reset. 
The result of the LINQ query is assigned to a range variable called the query object. The data source is not touched until you iterate on the query object, but if you iterate on the query object multiple times, you access the data source each time.

LINQ Providers:
.NET framework comes with a LINQ to Objects provider. The LINQ provider work as a middle tier between the datastore and the language environment.
To create a LINQ provider, we need to implement IQueryable interface. It has a Provider propety whose type is IQueryProvider, which is called to initialize and execute LINQ expressions.

Comments

Popular posts from this blog

Show Image on canvas HTML5

Here is the sample code to select image from system and display it on html5 canvas and javascript: <input type= "file" id= "selectedImage" /> <canvas id= "myCanvas" width= "500" height= "500" > </canvas> Javascript code: $( "#selectedImage" ).change( function (e) { var URL = window .URL; var url = URL.createObjectURL(e.target.files[ 0 ]); img.src = url; img.onload = function () { var canvas = document .getElementById( "myCanvas" ); var ctx = canvas.getContext( "2d" ); var imgSize = calculateAspectRatioFit(img.width, img.height, canvas.clientWidth, canvas.clientHeight); ctx.clearRect( 0 , 0 , canvas.width, canvas.height); ctx.drawImage(img, 0 , 0 , imgSize.width, imgSize.height); } }); function calculateAspectRatioFit(srcWidth, srcHeight, maxWidth, maxHeight) { var ratio = Math .min(maxWi

Pass byte array from C# to C++ and vice-versa

Pass byte array from C# to C++                           If you want to pass a byte array to native DLL as parameter, you can use the Intptr to do this, please check the demo below. /C++ API code: TestDLL_API void TestArrayPara (BYTE * pArray, int nSize) { for ( int i= 0 ; i<nSize; i++) printf( "%d\n" , pArray[i]); } //C# code: class TestClass { [DllImport(@"TestDll.dll")] public static extern void TestArrayPara (IntPtr pArray, int nSize); public static void Test () { byte [] array = new byte [ 16 ]; for ( int i = 0 ; i < 16 ; i++) { array[i] = ( byte )(i + 97 ); } int size = Marshal.SizeOf(array[ 0 ]) * array.Length; IntPtr pnt = Marshal.AllocHGlobal(size); try { // Copy the array to unmanaged memory. Marshal.Copy(array, 0 , pnt, array

Display Tooltip for Combo Box item C#.NET Winforms

In windows form combo box control sometimes while adidng items dynamically we have items whose width is greater than width of combox box control. In this case for making UI more user friendly we can show tooltip over such item. Here is the sample C# code to display such tooltip:  Add a Tooltip control on the form.  Add following code : this . combo_box1 . DropDownStyle = System . Windows . Forms . ComboBoxStyle . DropDownList; this . combo_box1 . DrawMode = DrawMode . OwnerDrawFixed; this . combo_box1 . DrawItem += new DrawItemEventHandler(combo_box1_DrawItem); this . combo_box1 . DropDownClosed += new EventHandler(combo_box1_DropDownClosed); this . combo_box1 . MouseLeave += new EventHandler(combo_box1_Leave); void combo_box1_DrawItem( object sender, DrawItemEventArgs e) { if (e . Index < 0 ) { return ; } string text = combo_box1 . GetItemText(combo_box1 . Items[e . Index