Question

How to use LINQ for entity classes

Asked by: RadicalSoftwareSolutions

Hi

I have a very simple requirement which I'm struggling to get my head round

I have linked my SQL datatables up to my VS2008 VB.NET app and I want to use the generated classes in the following manner (this is to keep it consistent with existing code structure which I inherited)
---------------------------------------------------------------------------------------------
dim _Customer as (some LINQ class - this is one of my questions)

_customer.get(me.cust_id.text)     'retrieves the customer record from the db
_customer.Turnover = 123456
_customer.update
----------------------------------------------------------------------------------------------

so it looks VERY simple but hwo do I get to do that with LINQ classes?

Many thanks in advance



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Asked On
2008-09-03 at 23:16:09ID23701659
Tags

vb.net

Topics

Language Integrated Query - LINQ

,

Microsoft Visual Basic.Net

Participating Experts
1
Points
500
Comments
4

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Answers

 

by: naspinskiPosted on 2008-09-03 at 23:30:42ID: 22384654

This is very simple, you just have to do a few things:

First, you have to make your DBML, which will make your DataContext class which is the go-between for LINQ and your DB.  To do this:
-Right click on your solution and add->new item, click LINQ-to-SQL Classes, name it something like 'Customers.dbml'
-Now that you are in your dbml, open your server explorer and find the table(s) you want to use from your database, and drag them into your dbml.  Save your DBML.

Now that that is made, you have your business layer set up and you can access it like this:

CustomersDataContext db = new CustomersDataContext();//allows you to use your dbml
 
var record = db.table_name.First(r => r.id == cust_id.text); //get the record you want to use
record.Turnover = 123456; //change value
db.SubmitChanges(); // submit the changes
 
//now this is in c#, I will check with the vb context

                                              
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by: naspinskiPosted on 2008-09-03 at 23:40:30ID: 22384691

Here is the syntax for VB.  I am calling your table as 'table_name' as I don't know it's real name :P

Dim db As New getPropertiesDataContext() 'prepare your data context'
Dim record = (From r In db.table_name Where r.id = CType(cust_id.text, Int32) Select r).First()
'you have to use First otherwise it will return an IEnumerable, not just a record'
record.Turnover = 123456
db.SubmitChanges()

                                              
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by: naspinskiPosted on 2008-09-03 at 23:41:04ID: 22384696

woops, forgot to change something

Dim db As New CustomersDataContext() 'prepare your data context'
Dim record = (From r In db.table_name Where r.id = CType(cust_id.text, Int32) Select r).First()
'you have to use First otherwise it will return an IEnumerable, not just a record'
record.Turnover = 123456
db.SubmitChanges()

                                              
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by: RadicalSoftwareSolutionsPosted on 2008-09-04 at 01:59:12ID: 31493055

Many thanks for excellent response - works a dream, saved me hours of searching

20120131-EE-VQP-002

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