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Override a Linq Datacontext Container

Posted on 2010-09-01
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Last Modified: 2012-05-10
I would like to have a sort of override on a specific class of a linq-2-sql.
Like when fetching data from that class, automatically use a filter.

Something.DataContext db = new Something.DataContext();
var items = db.Items.Where(d=>d.SomeValue > 10);

Which gave me a resultset to items.

The problem is, that I have rows in the items-table that reminds of a "visible = false" or a "validUntilDate < date" that I want to take care of without have to specify it everytime i use that class in the datacontext.

I will remember that  there are possible to create a sort of public partial class that inherits the datacontext and add something to it, which will be refered on use from elsewhere. Though, i'm not sure how to format and where to place it.

Some help would be nice!
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Question by:dingir
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13 Comments
 
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Expert Comment

by:Gururaj Badam
ID: 33579438
Why don't you try writing an extension method?
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Author Comment

by:dingir
ID: 33579524
Please guide me,
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Expert Comment

by:Gururaj Badam
ID: 33579587
what exactly you're trying achieve in your code? I may need that to help me understand it correctly before saying further
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Author Comment

by:dingir
ID: 33579859
Hi

I just want to continue getting data like

var items = db.Items.Where(d=>d.SomeValue > 10);

and feel safe that there are an underlying type/method that filter out the unwanted records,
which means something the above codes in princip rans on already filtered data, but you wouldnt recognize it.
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Expert Comment

by:Gururaj Badam
ID: 33580335
The Linq pattern will only allow you to write Query like expression. In this case the Where clause will help you to exclude unwanted objects. I don't think there's other way to do it.
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Expert Comment

by:nireliyahu
ID: 33588882
Hi,

i have a solution for you:

put in your class variable
public IQueryable<Item> FilteredItems;

and in your class ctor put the filter u want :

Something.DataContext db = new Something.DataContext();
FilteredItems =  db.Items.Where(i => i.visible == false || validUntilDate < date);

and than wrote youre quiry from   FilteredItems

var items = FilteredItems .Where(d=>d.SomeValue > 10);

with this solution you create any filter you want.
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Author Comment

by:dingir
ID: 33593784
Hi

Thanks. That will probably done it but still affect the way i / someone suspect to use the datacontext.

I feel there must be a way to put an override or psrtial class that being inherited by the datacontext class.

Maybe the problem lies in your answer. U can't, but can create a method that making it feel mostly like that.

Maybe a sort of db.items and a db.itemsfiltered. maybe also set the items datacontext class to private.
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Expert Comment

by:nireliyahu
ID: 33595872
Look i know that the datacontext overide solution is viable just need to search more.
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Author Comment

by:dingir
ID: 33698761
Something more on this topic?
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Expert Comment

by:Gururaj Badam
ID: 33698802
This is kind of Extension Method I was talking about. But like you see it's not straight forward and flexible too
public static class ListExtension
    {
        public static IList<T> Where<T>(this IList _list, int _filterValue)
        {
            IList<T> list = new List<T>();

            foreach (T item in _list)
            {
                if (item.SomeValue > _filterValue)
                    list.Add(item);
            }

            return list;
        }
    }

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Accepted Solution

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Gururaj Badam earned 500 total points
ID: 33698812
The other extension Method, in this you're not doing any good though. You're simply hardcoding the filter expression with the extension method which means it won't be flexible.

The original version is far better than this.
public static class DataContextExtension
    {
        public static IList<T> GetItems<T>(this DataContext _dataContext, int _filterValue)
        {
            return (from item in _dataContext.Items.Where(x => x.SomeValue > _filterValue) select item).ToList<T>();
        }
    }

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Author Comment

by:dingir
ID: 33722764
Your probably right. There might be a solution / several but no one of them doin any good with the drawbacks in mind.

I understand as that I need to use a stored procedure or database-stored view giving this full functionality?
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Author Closing Comment

by:dingir
ID: 33873381
We're both aware that the solution is accurace, but not optimal to the need,
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