LINQ to SQL (Part 4 - Updating our Database)
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by Scott Guthrie
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Northwind Database Modeled using LINQ to SQL

In Part 2 of this series I walked through how to create a LINQ to SQL class model using the LINQ to SQL designer that is built-into VS 2008.  Below is a class model created for the Northwind sample database and which I'll be using in this blog post:

Figure 1

When we designed our data model using the LINQ to SQL data designer above we defined five data model classes: Product, Category, Customer, Order and OrderDetail.  The properties of each class map to the columns of a corresponding table in the database.  Each instance of a class entity represents a row within the database table.

When we defined our data model, the LINQ to SQL designer also created a custom DataContext class that provides the main conduit by which we'll query our database and apply updates/changes.  In the example data model we defined above this class was named "NorthwindDataContext".  The NorthwindDataContext class has properties that represent each Table we modeled within the database (specifically: Products, Categories, Customers, Orders, OrderDetails).

As I covered in Part 3 of this blog series, we can easily use LINQ syntax expressions to query and retrieve data from our database using this NorthwindDataContext class.  LINQ to SQL will then automatically translate these LINQ query expressions to the appropriate SQL code to execute at runtime.

For example, I could write the below LINQ expression to retrieve a single Product object by searching on the Product name:

Figure 2

I could then write the LINQ query expression below to retrieve all products from the database that haven't yet had an order placed for them, and which also cost more than $100:

Figure 3

Note above how I am using the "OrderDetails" association for each product as part of the query to only retrieve those products that have not had any orders placed for them.


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User Comments

Title: Good Article   
Name: Vishnu Shanmugam
Date: 2010-12-11 12:46:40 AM
Comment:
Excellent article.
Title: very clear   
Name: tarun
Date: 2010-08-13 7:31:17 AM
Comment:
thanks for the clear explanation
Title: this is terrible   
Name: mac
Date: 2010-08-02 4:56:22 PM
Comment:
this is by far the worst display of CRUD i have seen yet.
Title: How can I insert dates   
Name: Ernie Smart
Date: 2010-03-17 1:08:05 PM
Comment:
How can I parse or convert dates? Let's say I have a text box (txtDate) to enter the dates and the database has a field called OrderDate. If either of the follwoing two:
OrderDate = Convert.ToDateTime(txtDate)
OrderDate = DateTime.Parse(txtDate)
I get System.FormatException: String was not recognized as a valid DateTime error.
If I do OrderDate = DateTime.Now, the code executes correctly.
How can convert the date entered in the text box so the program will work?
Thanks
Title: i can't find add,update or delete methods for my data context.   
Name: Enow Mbi
Date: 2010-02-19 11:10:15 AM
Comment:
GREAT ARTICLE.
I can't figure out why i can't find,add,update or delete methods of my data context despite the fact that my table has a primary key.
Title: More Article   
Name: twinsf
Date: 2010-01-28 2:09:59 AM
Comment:
thank youu for helpfull
Title: Bad advice   
Name: Simon
Date: 2008-12-28 11:59:06 PM
Comment:
The partial class validation logic you demonstrate is not testable and is therefore useless to me. Isn't it better advice to put the validation logic in business objects (as Rocky Lhotka would urge). Or alternatively, to put it in a service layer or repository that is testable. Baking your validation logic into these proprietary, tightly coupled, LINQ DTOs seems wrong.
Title: Create items together   
Name: Tom
Date: 2008-12-24 1:49:56 PM
Comment:
Is there a way to create a category and product together? From what I've seen, beverages.Products would be null, so you can't call "Add" on it. You also can't set Products equal to a new EntitySet, because the setter assumes a non-null EntitySet already which it calls "Assign" on.

Thanks!
Title: Very helpful   
Name: Alexander
Date: 2008-11-13 9:20:30 PM
Comment:
Just great. Killed a few days with msdn stuff trying to comprehend logic of Entity Insert/Update/Delete customisatiton. Just got it from this article in a couple of minutes.
Thank you.
Title: Linq doesn't update   
Name: Moez Tounsi
Date: 2008-10-07 12:15:53 PM
Comment:
Following the example above, ling will add a new record with the new parameters.
We have to handle the deletion of the old element.
Title: Excellent   
Name: Wayne
Date: 2008-07-23 12:27:59 AM
Comment:
Excellent article, Well done, a really good read.
Title: Thanks a lot   
Name: Andi
Date: 2007-12-02 11:25:10 AM
Comment:
Thank you for this great article!!!






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