Re: VS2008: How to access properties of a table in O/R designer

  • From: "Ricks Place" <OFBGMail@xxxxxxxxx>
  • To: <programmingblind@xxxxxxxxxxxxx>
  • Date: Sat, 14 Jun 2008 11:21:09 -0400

Thanks for the write-up Varun. I will take a further look at coding syntax for LINQ. Have you done any cross table or multi-table queries and inserts using transactions or anything that would require accessing multiple tables? I am thinking of something llike an insert running as a transaction requireing 2 tables to be updated or a rollback to occur.Also, have you tried any joins on multiple tables? 

Rick Farmington Mich. USA
----- Original Message ----- From: "Varun Khosla" <varun.lists@xxxxxxxxx> 
To: <programmingblind@xxxxxxxxxxxxx>
Sent: Saturday, June 14, 2008 4:31 AM
Subject: Re: VS2008: How to access properties of a table in O/R designer



Hi Rick,
See below why you may find LINQ more easier than ADO.net.


Language-Integrated Query (LINQ)

Language-Integrated Query (LINQ) is a set of features in Visual Studio
2008 that extends powerful query capabilities to the language syntax
of C# and Visual Basic. LINQ introduces standard, easily-learned
patterns for querying and updating data, and the technology can be
extended to support potentially any kind of data store. Visual Studio
2008 includes LINQ provider assemblies that enable the use of LINQ
with .NET Framework collections, SQL Server databases, ADO.NET
Datasets, and XML documents.


Language-Integrated Query (LINQ) is a groundbreaking innovation in
Visual Studio 2008 and the .NET Framework version 3.5 that bridges the
gap between the world of objects and the world of data.

Traditionally, queries against data are expressed as simple strings
without type checking at compile time or IntelliSense support.
Furthermore, you have to learn a different query language for each
type of data source: SQL databases, XML documents, various Web
services, and so on. LINQ makes a query a first-class language
construct in C# and Visual Basic. You write queries against strongly
typed collections of objects by using language keywords and familiar
operators. The following illustration shows a partially-completed LINQ
query against a SQL Server database in C# with full type checking and
IntelliSense support.


In Visual Studio you can write LINQ queries in Visual Basic or C# with
SQL Server databases, XML documents, ADO.NET Datasets, and any
collection of objects that supports IEnumerable or the generic
IEnumerable<(Of <(T>)>) interface. LINQ support for the ADO.NET Entity
Framework is also planned, and LINQ providers are being written by
third parties for many Web services and other database
implementations.

You can use LINQ queries in new projects, or alongside non-LINQ
queries in existing projects. The only requirement is that the project
target version 3.5 of the .NET Framework.

http://msdn.microsoft.com/en-us/library/bb397897.aspx

You can even now query variables as if they are database objects! :-)


On 6/12/08, Ricks Place <OFBGMail@xxxxxxxxx> wrote:
Man! That looks way diferent than Ado or even regular old Select statements! That problem with the ReadOnly is the one I have run up against. It is the 
same in DataSet methodology. We are working with PreDefined rows in the
schema so any changes must be applied to an instance of the PreDefined row and if we select only 2 columns and tried to update them the other columns 
would not have any values because they were not a part of the original
select statement. Have you found Linq any easier than Ado? It looks verbose. 
Rick USA
----- Original Message -----
From: "Varun Khosla" <varun.lists@xxxxxxxxx>
To: <programmingblind@xxxxxxxxxxxxx>
Sent: Wednesday, June 11, 2008 12:47 AM
Subject: Re: VS2008: How to access properties of a table in O/R designer



Hi Ricks,
In linq when we query the database like this:
dim resultRow = (from tableVar in dataContext.TableName where
tableVar.key = matchingKeyVar select tableVar).take(1).single()

the resultRow variable is filled up with first row resulting from the
where condition. Now suppose the queried table has 15 columns, and we
want to update the value of column5&6, we can do that like this:
resultRow.column5 = "some value"
resultRow.column6 = "some another value"
And call submit changes like this:
dataContext.SubmitChanges()
It will update those two columns. since resultRow contained values of
all the 15 columns, we don't need to specify the value of each but
only those which we want to update.
But if you had specified a select statement in the linq query like this:
dim resultRow = (from tableVar in dataContext.TableName where
tableVar.key = matchingKeyVar select tableVar.column5,
tableVar.column6).take(1).single()
This query will result in only two columns being members of resultRow,
but as I have seen, these columns are read-only and you cannot change
their value.

HTH

On 6/8/08, Ricks Place <OFBGMail@xxxxxxxxx> wrote:

Hi Guys:
Along these lines:
When I use a DataTable, DataSet, I get Rows on any select. I can limit
the
data returned to a couple of columns but it seems I have to provide
values
for an entire row or the values are messed up during an update. I don't
think I can just set and update a couple of columns using the DataSet
Update
function. Is this the case with Linq? Can you just Select a couple of
columns, set them and then apply an update for them or will that tip
other
columns in the original row?
I hope I explained this well enough to understand and my understanding is 
correct. I had problems like this some time ago so always just read
entire
rows, update whatever columns I want then ReWrite the entire row. This
is,
of course, pretty inefficient and I even had to write a TableAdapter
extension to avoid Optimistic Concurrency for a particular update since
it
was so blasted slow and unnessisary for the particular update.
Anyway, while on the Linq topic I thought I would ask in case someone has 
had experience with this situation.
Rick Farmington Mich. USA
If you knowal Message -----
From: "Varun Khosla" <varun.lists@xxxxxxxxx>
To: <programmingblind@xxxxxxxxxxxxx>
Sent: Sunday, June 08, 2008 3:10 AM
Subject: Re: VS2008: How to access properties of a table in O/R designer 



By the way, I've found an alternative for this. Locate the table in
the designer window, press shortcut key, open add sub-menu, click
property - it will take you to the list of the columns for that table
focussing an edit box forcing you to specify a name for the new
property. Pressing the shift+tab creates a new property with the
default name property1, since it's not required one can delete it by
selecting it in the listbox and pressing the dell key.

I know that this is not the right way to go about it, but this is the
only way I'm able to know to go about it. (smile)


On 6/7/08, Varun Khosla <varun.lists@xxxxxxxxx> wrote:

P.P.S. is additional postscript

On 6/1/08, Chris Hallsworth <christopherhallsworth71@xxxxxxxxxxxxxx>
wrote:

Hi what's PPS? I've heard of PS but not PPS? Thanks and sorry for my
ignorance.
--
Chris Hallsworth
  ----- Original Message -----
  From: Varun Khosla
  To: programmingblind@xxxxxxxxxxxxx
  Sent: Monday, June 02, 2008 8:13 AM
Subject: VS2008: How to access properties of a table in O/R designer 


  Hello listers,
  Has anybody worked on VS2008? It has new feature called LINQ
(Language-Integrated Query) designed to further increased the
speed/object
orientation of working with database. It has added an O/R designer for 
this
purpose. User can drag-drop tables from server explorer to the
designer
to
create a data context which is the focle point of LINQ.
Dragging/dropping
part is okay because Jaws has a shortcut key for this purpose. The
problem
I'm facing is how to access properties of the table object (don't
confuse
properties here with the general properties of any components such as 
Name
which can be accessed via f4 in O/R as well, but with the properties
here
I
mean by columns of a table) so that I can delete specific columns that 

I
don't require (only from the table class of O/R designer and not from 
the
database).

  Has anybody gotten an idea as to how it can be done?
P.S. I've not been able to find a shortcut key for this anywhere on 
the
net.
  P.P.S. Sighted folks can access it with the mouse, but there's no
text
written at that point to make jaws cursor do the job.

  Thanks

  --
  Varun



--
Varun




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