How to create a simple data access layer

[Jeet2004]

Hi,
It might be simple but i dont know how to go about it. I have all my sql calls and code in the app itself and now i have been told to have all data base iterations using data access layer. Now Q's i have is
1. what all should be there in a DAL
2. how to create one

Any code snippets would be appreciated.
Thanks.

 

[Juice05]

I would create a Module called DAL and within it put all functions and procedures that contact the database. If you are using stored procedures this will help as far as reusablility of code.

 

[Jeet2004]

Juice05 do you have any code sample or example code or a url ??

 

[Juice05]

Code for what? Just create a module and move all of your functions and procedures into that module. When you access it just reference the module and then function or procedure.

 

[BobRodes]

Generally, putting things in a 3 tier (presentation, business, data) architecture involves creating classes. Do you need help with this?

Bob

 

[Jeet2004]

Actually what i need is an example to look at how the data access layer is created.
I guess you have function to connect to database, disconnect and what else?

Please let me know if i am not clear ?

 

[chiph]

You would have methods for your basic CRUD operations: to create, retrieve, update, and delete rows from each of your tables.

You're not limited to one of each, of course. You could have both RetrieveById and RetrieveByLastName methods.

Chip H.


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[BobRodes]

Are you familiar with ADO?

 

[Jeet2004]

yeah

 

[BobRodes]

Well, that's how you do it. Read up on ADO to get functions to connect, disconnect and so on. As for "what else?" you'll need to basically view and alter the data.

You also need to put your data routines into objects, and retrieve the data by using those objects.

As for what should be in the data access layer, all the routines that involve getting and changing data should, expressed in terms of a group of related classes.

Bob

 

[BobRodes]

<I guess you have function to connect to database, disconnect and what else?

Yes, to both of those, and use an ADO Connection object. As for what else, you need to retrieve data and/or alter it. Depends on your business rules.

Basically, get clear on what you want to see (Presentation layer), and what data you want to store (data layer). How do you interact between these two? (Business layer.) Does the presentation layer permit alterations to the data? (Can you enter values into the database from a window?) What kind of data needs to show in the window?

Once you have answered these questions for yourself, it might be easier for you to ask deeper questions, and get deeper answers.

HTH

Bob

 

[Jeet2004]

Thanks bob for your patients and suggestions.
Appreciate your help.

 

[BobRodes]

You're welcome. Feel free to ask further as you move along.

Bob