Thursday, 17 May 2012

C# Programming : Get selected fields LINQ query using LINQ To Objects

There are situations where you do not want all fields in LINQ query you want only selected fields.
You can also say that Creating a custom projection with LINQ.
Here are sample example for that.
In this Example we only want Title and ISBN Fields.

C# Example :
    public class Books
    {
        public string Title { get; set; }
        public string ISBN { get; set; }
        public DateTime ReleaseDate { get; set; }
        public int Pages { get; set; }
    }

    protected void Page_Load(object sender, EventArgs e)
    {
        var bookslist = GetBooksList();
        //var query = from bl in bookslist select bl;
        var query = from bl in bookslist
                    select new { bl.Title,bl.ISBN };
        this.gvBooks.DataSource = query;
        this.gvBooks.DataBind();
    }
    public List<Books> GetBooksList()
    {
        return new List<Books> {
                        new Books { Title="ASP.NET",ISBN="asp1",ReleaseDate= DateTime.Parse( "11/11/2010") ,Pages=200},
                        new Books { Title="C#.NET",ISBN="c#2",ReleaseDate= DateTime.Parse( "10/11/2010") ,Pages=500},
                        new Books { Title="VB.NET",ISBN="vb3",ReleaseDate= DateTime.Parse( "5/5/2009") ,Pages=400},
                        new Books { Title="SQL Server",ISBN="sql4",ReleaseDate= DateTime.Parse( "6/9/2010"),Pages=300 },
                        new Books { Title="JAVA",ISBN="java5",ReleaseDate= DateTime.Parse( "8/5/2011"),Pages=400 }
        
        };

    }

VB.net Example :
    Public Class Books
        Public Property Title() As String
        Public Property ISBN As String
        Public Property ReleaseDate As Date
        Public Property Pages As Integer
    End Class
    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Dim bookslist = GetBooksList()
        'Dim query = From bl In bookslist _
        '            Select bl
        Dim query = From bl In bookslist _
                    Select New With {bl.Title, bl.ISBN}
        gvBooks.DataSource = query
        gvBooks.DataBind()
    End Sub
    Public Function GetBooksList() As List(Of Books)
        Dim lstBooks As New List(Of Books) From { _
                                New Books With {.Title = "ASP.NET", .ISBN = "asp1", .ReleaseDate = DateTime.Parse("11/11/2010"), .Pages = 200}, _
                                New Books With {.Title = "C#.NET", .ISBN = "c#2", .ReleaseDate = DateTime.Parse("10/11/2010"), .Pages = 500}, _
                                New Books With {.Title = "VB.NET", .ISBN = "vb3", .ReleaseDate = DateTime.Parse("5/5/2009"), .Pages = 400}, _
                                New Books With {.Title = "SQL Server", .ISBN = "sql4", .ReleaseDate = DateTime.Parse("6/9/2010"), .Pages = 300}, _
                                New Books With {.Title = "JAVA", .ISBN = "java5", .ReleaseDate = DateTime.Parse("8/5/2011"), .Pages = 400}}

        Return lstBooks
    End Function

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