New keyword and polymorphism

The new keyword will block inherited methods referring to normally overridden methods.

In this case the base method will be called

public class Parent

    {

        public void msgShow2()

        {

            MessageBox.Show(this.show2()); 

        }

       

       

        public virtual string show2()

        {

            return "parent" + this.GetType().ToString();

        }

       

        public virtual string  show()

        {

            return  "parent" + this.GetType().ToString();   

        }

    }

public class Child1 : Parent

    {

        public override string show2()

        {

            return "Child1:override" + this.GetType().ToString();

        }

       

        public override string show()

        {

            return "Child1" + this.GetType().ToString();

        }

        public void message()

        {

            MessageBox.Show("Child1"); 

        }

    }

public class Child2 : Parent

    {

        public new string show2()

        {

            return "Child1:new" + this.GetType().ToString();

        }

        public override string show()

        {

            return "Child2" + this.GetType().ToString();

        }

        public void message()

        {

            MessageBox.Show("Child2");

        }

    }

            Running the following

            Child1 c1 = new Child1();

            Child2 c2 = new Child2();

            List<Parent> l = new List<Parent>();

            l.Add(c1);

            l.Add(c2);

            foreach (Parent p in l)

            {

                p.msgShow2();

              //c1 will be derived

              //c2 will call the base

            }

what causes a InvalidCastException?

when a parent reference refers to a child - then casting to the child works fine

Parent pt ;
pt = c1;
((Child1)pt).message();

When a parent object is instantiated, likewise this will work

Parent pt = new Parent() ;
pt = c1;
((Child1)pt).message();

However a child object set to a parent will not compile
Parent pt = new Parent();

c1 = pt;

and an explicit cast will cause a runtime error  InvalidCastException

Parent pt = new Parent();
c1 = (Child1)pt;//invalidcast


if however the parent is referencing a child then of course there is no runtime error

Parent pt = new Parent();
pt = c1;
c1 = (Child1)pt;

why is there explicit casting in c#

there are 2 basic places where this is needed - when the precision is being truncated in numeric value types
and to access the members of actual type ;for example, if a child object is referenced by a parent then to get to the childs method you would need
   
   ((Child1)parent1).message()
I believe that with a number (1).ToString() works because it is implicitly being casted to object

Cool things cross apply does

select * from

(

select 1 as customer_id, 'herby' as name

union select 2 as customer_id, 'george' as name

union select 3 as customer_id, 'ben' as name

) a

cross apply

(

select customer_id, sale,date,

sum(sale) over(partition by customer_id,month(date)) total_of_cust_month,

sum(sale) over(partition by month(date)) total_of_month

from

(

select 1 as customer_id, 34.67 as sale, '1/1/2011' as date

union select 1 as customer_id, 3464.67 as sale, '2/1/2011' as date

union select 1 as customer_id, 364.67 as sale, '2/5/2011' as date

union select 1 as customer_id, 3374.67 as sale, '3/1/2011' as date

union select 2 as customer_id, 3448.67 as sale, '1/1/2011' as date

union select 2 as customer_id, 3324.67 as sale, '2/1/2011' as date

union select 2 as customer_id, 4.67 as sale, '2/4/2011' as date

union select 2 as customer_id, 3443.67 as sale, '3/1/2011' as date

union select 3 as customer_id, 3344.67 as sale, '1/1/2011' as date

union select 3 as customer_id, 3544.67 as sale, '2/1/2011' as date

union select 3 as customer_id, 3.67 as sale, '2/3/2011' as date

union select 3 as customer_id, 6334.67 as sale, '3/1/2011' as date) as main

where main.customer_id = a.customer_id

) b

cool things

1. we can get multiple rows - subqueries cant
2. we can get multiple columns - subqueries cant

example of cross join

select * from 

(select 1 id , 'ball' item

 union select 2 id , 'bat' item

 union select 3 id , 'glove' item

) as a

cross join

(select 'New York' location

 union select 'Philadelphia' location

 union select 'Miami' location )

as b

google maps api key change

I used the windows 7 search for where the maps api was being called in a certain website - the search did not look into .master pages - pain in the neck.

I set it at the map call level and that helped on my local development environment but not on the website

I eventually found it in the master page and all is well

BTW visual studio didnt search the master pages either -

TABLESAMPLE example

SELECT
FROM id, name dbo.customers TABLESAMPLE SYSTEM(20 PERCENT)

BTW - This is better than the classic method of getting sample data
       select top 5 * from stats order by  newid()    
because in large amounts time will be spent creating the GUID

comma delimited lists in sql server

once upon a time I did this with cursors (cursors, cursors I say!)

  this is easier:

ALTER PROCEDURE [dbo].[getCommaDelim]

AS

BEGIN

      -- SET NOCOUNT ON added to prevent extra result sets from

      -- interfering with SELECT statements.

      SET NOCOUNT ON;

    declare  @list varchar(1000)

set @list = ''

   

      SELECT @list =@list + name + ',' from customers

select @list

END

if the @list is not set thusly:
set @list = ''
then the result will be null

intersect example

SELECT numFROM(SELECT 0 AS numUNION ALL
SELECT 0 AS Expr1UNION ALL
SELECT 5 AS Expr1UNION ALLSELECT - 55 AS Expr1) AS aINTERSECT
SELECT numFROM(SELECT 0 AS numUNION ALL
SELECT 0 AS Expr1UNION ALL


results : 0,5

Unions vs Union All

Unions return unique values - even from seperate selects

SELECT     num

FROM         (SELECT     0 AS num

                       UNION ALL

                       SELECT     0 AS Num

                       UNION ALL

                       SELECT     5 AS Num) AS a

UNION

SELECT     num

FROM         (SELECT     0 AS num

                       UNION ALL

                       SELECT     0 AS Num

                       UNION ALL

                       SELECT     5 AS Num) AS b

 returns 0,5
union all doesn't remove doubles in seperate selects  and returns
0
0
5
0
0
5

Join imitating not exists

select *  from

(

select 1 id,'herby' name

union select 2 id,'john' name

) a

left join

(select 1 id ,23.56 amount) b

on a.id = b.id

where b.id is null

except acting like a not in or not exists

with test (id,name)

as

(

select 1 id,'herby' name

union select 2 id,'john' name

)

select * from test

where id in

(

select id from test

except

 select 1 id

)

interesting sql tidbit

this:
(

select 3 as herby

union select 1

)

order  by herby

works

with group by - it doesnt

you need:

select * from

(

select 3 as herby

union select 1

) as main

group by main.herby

why do you need exists - why isnt an inner join enough?

inner join returns multiple rows

theoretically the database could quit looking for a specific row after its true


perhaps another reason why there is exists so there could be not exists

why are there events?

when you can handle events with a public intance of a delegate?

1)to disallow = operator , events allow only +=
2)to disallow delegate being directly called - with events it only works with an event handler

Proof that windowing comes last before order by

select id ,item, count(*) over()-- ,

-- sum(price) over(partition by id  )

/* running totals dont work yet */

from

(

select 1 id , 'beans' item, 1.66 price

union

select 2 id , 'tomatoes' item, 3.66 price

union

select 3 id , 'potatoes' item, 6.66 price

union

select 4 id , 'chips' item, 1.36 price

) main

where main.id <4

Giving CLR functions rights to writes

I created a CLR function to write to a file. This of course raised a permissions error to files

The following is what I had to do to get it to work

1)Check who is the owner of the database – make sure it’s the same as master

SELECT name, SUSER_SNAME(owner_sid)

FROM   sys.databases

2)If different

ALTER AUTHORIZATION ON database::xversions TO sa;

(or EXEC sp_changedbowner 'sa')

GO

3)Create the assembly with EXTERNAL_ACCESS

create assembly TSQLFunctions

from

'c:\program files\assemblies\TSQLFunctions.dll'

WITH PERMISSION_SET=EXTERNAL_ACCESS

go

how to script all stored procedures etc in a sql database

how to find who is locking a document

view state gaffe

a common error in  O'Reilly's programming c# 3.0 - that viewstate is needed for retaing choices in drop downs- the following disproves that: 

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="test_view_state._Default"  %>

<%@ Register src="property.ascx" tagname="property" tagprefix="uc1" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" >

<head runat="server">

    <title>Untitled Page</title>

</head>

<body>

    <form id="form1" runat="server">

    <div>

        <asp:Button ID="Button1" runat="server" Text="Button" onclick="Button1_Click" />

        <asp:Label ID="Label1" runat="server"

            Text="Label"></asp:Label>

        <asp:Button ID="Button2" runat="server" Text="Button" onclick="Button2_Click" />

       

        <br />

        <asp:ListBox ID="ListBox1" runat="server">

            <asp:ListItem>1</asp:ListItem>

            <asp:ListItem>2</asp:ListItem>

            <asp:ListItem>3</asp:ListItem>

        </asp:ListBox>

       

    </div>

    <uc1:property ID="property1" runat="server"  Text ="hhhhh"  />

    </form>

    </body>

</html>

namespace test_view_state

{

    [Author("george", version = 1.1)]

    public partial class _Default : System.Web.UI.Page

    {

        [Conditional("DEBUG")]

        private void callout()

        {

            this.EnableViewState = false;

        }

        protected void Page_Load(object sender, EventArgs e)

        {

        }

    }

    [System.AttributeUsage(System.AttributeTargets.Class |

                       System.AttributeTargets.Struct)]

    public class Author : System.Attribute

    {

        private string name;

        public double version;

        public Author(string name)

        {

            this.name = name;

            version = 1.0;

        }

    }

}