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How to handle multiple users

I have a page which has a text box at the top. When the page is loaded, the code runs for the value of text box i.e Textbox.text= something. The logic of that code is:
bring the last value of the specific column of specific table from database (Integer always)
add 1 to it
show in text box.
It works perfectly fine. But I want to know that if two users are accessing the same page how should I handle this scenario when page is loaded.
Example the last value in DB column was 8 when the page loaded it incremented it and showed 9 in text box.
But what if two users loaded the page same time on different browsers it will cause problem because I don't want duplicate in my columns.

What you can do here is before you insert into db first get the last value from the colum and then +1 the value and then insert it into db.
but there is one catch which is if your User1 and User2 are seeing 8 value in textbox and User1 clicks on button 9 will get stored in db column and then User2 clicks on button 10 value will get stored.

Your best bet would be to load the database value into memory (e.g. a static variable) and have a method that uses a lock before incrementing and returning the result to the respective users. e.g.
private static object _syncRoot = new object();
private static int? dbValue;
public static int GetNewDbValue()
{
if (dbValue == null)
{
// load db value from database
}
// lock ensures only one user can increment at a time
lock (_syncRoot)
{
dbValue++;
return dbValue;
}
}
This will work as long as you are not running a web farm or load balancing. If you want to stay away from static, by all means you can, just make sure the object you use instead is centrally accessible.

Get Identity Attribute value before inserting in Database

I have a table and it has one of the attribute set as identity. I want to get the value of the identity attribute that would be generated after I enter a value to the database.
I have EmpTable made of EmpID and EmpName. EmpID is set as Identity. I want to fetch the EmpID value before inserting a new row to the database.

I would advise against trying to do this with a table that is set up to use an integer column as the primary key. You will run into concurrency problems if you simply fetch the previous ID and increment it. Instead you should use a GUID (uniqueidentifier in SQL) as your primary key.
This will allow you to generate a new GUID in your code that can safely be saved to the database at a later stage.
http://msdn.microsoft.com/en-us/library/system.guid.newguid.aspx
http://msdn.microsoft.com/en-us/library/ms187942.aspx

Sure the server knows where the auto-increment count is in its sequence, but there is almost nothing useful you can do with that information. Imagine you go to the Post Office and they hand out numbered tickets so they can serve customers in order. Of course you could ask them what the next number they'll give out is, but since anyone can walk in at any time you don't know you'll get that number. If you don't know that you'll get it, you can't do anything with it - e.g. writing it as a reference number on a form would be a mistake.
Depending on what you're trying to do, your two main options are:
Use a client-generated guid as your identifier. This kind of messes up the order so the analogy isn't great, but imagine if each customer who walked in could generate a random number that they are sure would never have been used before. They could use that to fill out forms before taking a number.
Take a number, but do it in a transaction with the other operations. A customer can take a number and use it to fill out some paperwork. If they realize they left their money at home, they just throw everything away and you never call their number.
Why do you think you need this information? Can you use either of these strategies instead?

How to set a property value to auto increment in visual studio lightswitch 2012

i want to set a property value in a table to default auto increment,but their are no options to do so in lightswitch2012 to my knowledge which is given that i recently started learning lightswitch,very light.
ok heres the real problem,this is the table
[customer][id,customer_id,name]
i want to set customer_id by default to id unless it is manually changed to different value.
how to acheive this?

In the Entity designer make your Customer_ID not required.
Write Code for Customers_Inserted.
Then, check to see if the Customer_ID is null. If it is, copy the ID field to it.
private void Customers_Inserted(Customer entity)
{
if (entity.Customer_ID == null) {
entity.Customer_ID = entity.ID;
}
}

You're right, there is no "auto-increment" data type available in LightSwitch. The ID property auto-increments, but that's a special case, handled by LightSwitch.
If you were attaching to an external SQL database, if you added a column that was an Integer Identity column, although it'll just appear as an Integer property in LightSwitch, it would still auto-increment because that's actually done in the SQL database itself.
The problem with all auto-increment properties is that you won't get the actual value until the record is saved.
Can I ask why you need an auto-increment property?

I may be misunderstanding what you are trying to achieve, but if you are using either a table or a grid, and you want to set the values for various entities for each new row your user adds (like customer_id = id, etc.), you can use the _Changed method and Add event to programmatically set any of the new row entities.
If this is along the lines of what you're looking for, watch Beth Massi's video How Do I: Copy Data from One Row into a New Row? You should be able to adapt her code to accomplish what you have in mind I think.

"Predict" next model ID

Sheesh...
I think this can be done but I just can't figure it out at the moment.
So I've created this app, that's working fine. But for some reason (too long to explain sorry) I would need to predict next ID to come from data table.
Note that last id + 1 will not work. I've tried this.
var lastProperty = db.Properties.OrderByDescending(p => p.PropertyID).FirstOrDefault();
int propID;
if (lastProperty == null)
{
propID = 1;
}
else
{
propID = 1 + lastProperty.PropertyID;
}
And as long as properties don't get deleted it works...
As soon as one is deleted, it messes up of course, since lets say we delete 6th Property,
last one will be 5th now, and with that code we'll get 6 5(last one) + 1, and I save my model related to Property with PropertyID 6 which I got from that code, and next Property will be 7 since database still remembers that 6 existed and was deleted... Model I intended to have same PropertyID as THAT last Property will not have it, and it'll fail...
Also, I can't add this AFTER saving Property, I realize that might seem as a solution but it's not. It has to be predicted.
Thank you... Please help...
UPDATE
This is the use case I'm trying to accomplish.
Property model with ID Name DataType properties.
List model with ID ListValue PropertyID properties.
When new Property is created user types in the Name, and from premade dropdown list for DataType selects a value, if that value is List, it opens additional form that contains a listbox, textbox and a button (add_Button). User types in the value in a textbox, and clicks the add_Button to add it to List.
Listbox is populated from List model, and add_Button, saves values from textbox to ListValue property of List, also as you've seen, I'm trying to manually add PropertyID to List by predicting it's value...
Then, upon finishing adding all the elements wanted through textbox, by clicking Create button, Property is then saved.
Hope this was clear enough.

It seems like you want to know the current state of the identity column:
SELECT IDENT_CURRENT('Table')

When need to know what your primary key values are going to be before committing to the Db you could use a uniqueidentifier (GUID) as the Pk for your Property and therefore as the Fk for your List entity. That way you can create it your self and it'll always be unique on committal.

You mention Entity Framework, have you tried adjusting your model?
StoreGeneratedPattern can be adjusted to allow automatic update of your local model when you store to the database.

Defining Status of data via Enum or a relation table

I have an application which has rows of data in a relation database the table needs a status which will always be either
Not Submitted, Awaiting Approval, Approved, Rejected
Now since these will never change I was trying to decide the best way to implement them I can either think of a Status enum with the values and an int assigned where the int is placed into the status column on the table row.
Or a status table that linked to the table and the user select one of these as the current status.
I can't decide which is the better option as I currently have a enum in place with these values for the approval pages to populate the dropdown etc and setup the sql (as it currently using to bool Approved and submitted for approval but this is dirty for various reasons and needs changed).
Wondering what your thought on this were and whether I should go for one or the other.
If it makes any difference I am using Entity framework.

I would go with the Enum if it never changes since this will be more performant (no join to get the status). Also, it's the simpler solution :).

Now since these will never change...
You can count on this assumption being false, and sooner than you think.
I would use a lookup table. It's far easier to add or change values in a lookup table than to change the definition of an enum.
You can use a natural primary key in the lookup table so you don't need to do a join to get the value. Yes a string takes a bit more space than an integer id, but if your goal is to avoid the join this will accomplish that goal.

I use Enums and use the [Description("asdf")] attribute to bind meaningful sentences or other things that aren't allowed in Enums. Then use the Enum text itself as a value in drop downs and the Description as the visible text.