Business logic for property on LINQ class

[wdudek]

Hi,

I have a situation where I am writing an applicaiton against a legacy
database that uses Y/N for it's boolean fields. Using LINQ I generated a
class that exposed these fields as a char. What I would like to do is expose
them to consumers of the class as a bool. I tried to edit the property that
was autogenerated by LINQ but this didn't work and caused numerous compiler
errors.
Is there a recomended approach to doing this? so far the only way I can
see to achieve this would be to wrap the LINQ class inside of another one and
expose it to the calling code through this wrapper, using a property marked
internal to allow code inside my library to work against the LINQ generated
class and the data context.
Any thoughts? in the end I want to achieve this

char _myValue;

public bool MyValue
{
get
{
if (_myValue)
return 'Y';
else
return 'N';
}
set
{
char temp = value ? 'Y' : 'N';
if (_myValue != temp)
_myValue = temp;
}


}


thanks Bill

 

[Steven Cheng [MSFT]]

Hi Bill,

From your description, you have an existing database table which contains a
single char column(represent boolean state), the LINQ class will generate
the table field as char, and you're wondering how to make the column/field
become boolean so as to ease the operation of the data at front layer,
correct?

As for this case, in my opinion, if the most requirement is make your front
layer(such as UI layer) be able to process with the object with that field
as boolean(instead of char), I think you can use LINQ query to customize
the output records. For example:

# suppose "cbcontext.cb_tables" is the generatred linq table which contains
that 'char' column

======================
private void button1_Click(object sender, EventArgs e)
{
LinqTestApp.cb_linqDataContext cbcontext = new
cb_linqDataContext();

var items = from c in cbcontext.cb_tables
select new {c.id, c.name, Enabled=
c.enabled=='Y'?true:false};

dataGridView1.DataSource = new BindingSource(items,"");

}
==============================

the query use a new class object(I used anonymous object while you can
define a typed class if you want) which contains boolean field(converted
from the char field in the original table class).

Then, you can use the modified output datas in other UI controls or code.
This can keep the generated DataContext and table mapping unchanged(this is
preferred as the automatically generated table mapping reflect the actual
underlying database table schema).

Another approach is adding some addtional method on your DataContext which
execute custom SQL script. Then, you can consider make the field converting
at SQL script layer(use T-SQL to convert the char value to a bool field).

#LINQ to SQL (Part 8 - Executing Custom SQL Expressions)
http://weblogs.asp.net/scottgu/archive/2007/08/27/linq-to-sql-part-8-executi
ng-custom-sql-expressions.aspx

IMO, I would prefer the first approach since it require minimal changes in
code. How do you think?

Sincerely,

Steven Cheng

Microsoft MSDN Online Support Lead


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--------------------

 

[wdudek]

I'm probably going to take your appraoch to this, I was hoping that I would
be able to mess with the property generated by the linq code so that if
anyone else I work with tried to use the library it owuld be more obvious to
them what this field was.

Thanks

Bill

 

[Steven Cheng [MSFT]]

Thanks for your reply Bill,

Yes, it'll be nice if we can directly assocate the generated linq table
property to our new property logic. Anyway, I think so far it's better to
keep the original generated code as that'll ensure the LINQ work correct
with the backend database table.

Also, another idea is you can add an additional custom property in the
auto-generated LINQ table class which use the auto-generated property to
calculate the actual property value you want to use in front end code.
Here is an example, I used a separated partial class code file to define
this propety so that it won't be overwrite when the IDE regenerate the LINQ
class code:

#"MyTable" is the table class name autogenarated by IDE
====================================

public partial class MyTable
{
public bool MyEnabled
{
get
{
return _enabled == 'Y' ? true : false;
}

set
{
_enabled = value ? 'Y' : 'N';
}
}
}

====================================

And in your LINQ query code you can just return object collection of the
generated Table class,but choose to use the certain properties(that you
want to use).

Hope this also helps.

Sincerely,

Steven Cheng

Microsoft MSDN Online Support Lead


Delighting our customers is our #1 priority. We welcome your comments and
suggestions about how we can improve the support we provide to you. Please
feel free to let my manager know what you think of the level of service
provided. You can send feedback directly to my manager at:
(e-mail address removed).

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--------------------

From: =?Utf-8?B?d2R1ZGVr?= <[email protected]>
References: <[email protected]>

Subject: RE: Business logic for property on LINQ class
Date: Wed, 6 Aug 2008 07:57:01 -0700

 

[wdudek]

I like that, I'm not at a project with LINQ to SQL right now, but I'm
assuming I can even make the other properties I'm trying to hide private or
internal to completely achieve what I was originally looking for in effect at
least.

Thanks
Bill

 

[Steven Cheng [MSFT]]

Thanks for the followup Bill,

No problem. If you continue to work on this later and need any help, please
feel free to post here.

Sincerely,

Steven Cheng

Microsoft MSDN Online Support Lead


Delighting our customers is our #1 priority. We welcome your comments and
suggestions about how we

can improve the support we provide to you. Please feel free to let my
manager know what you think of

the level of service provided. You can send feedback directly to my manager
at: (e-mail address removed).

--------------------

From: =?Utf-8?B?d2R1ZGVr?= <[email protected]>
Subject: RE: Business logic for property on LINQ class
Date: Thu, 14 Aug 2008 13:19:02 -0700