LINQ to SQL (Part 4 - Updating our Database)
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by Scott Guthrie
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Updates across Relationships

What makes O/R mappers like LINQ to SQL extremely flexible is that they enable us to easily model cross-table relationships across our data model.  For example, I can model each Product to be in a Category, each Order to contain OrderDetails for line-items, associate each OrderDetail line-item with a Product, and have each Customer contain an associated set of Orders.  I covered how to construct and model these relationships in Part 2 of this blog series.

LINQ to SQL enables me to take advantage of these relationships for both querying and updating my data. For example, I could write the below code to create a new Product and associate it with an existing "Beverages" category in my database like so:

Figure 8

Note above how I'm adding the Product object into the Category's Products collection.  This will indicate that there is a relationship between the two objects, and cause LINQ to SQL to automatically maintain the foreign-key/primary key relationship between the two when I call "SubmitChanges()".

For another example of how LINQ to SQL can help manage cross-table relationships for us and help clean up our code, let's look at an example below where I'm creating a new Order for an existing customer.  After setting the required ship date and freight costs for the order, I then create two order line-item objects that point to the products the customer is ordering.  I then associate the order with the customer, and update the database with all of the changes.

Figure 9

As you can see, the programming model for performing all of this work is extremely clean and object oriented. 


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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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