在Linq2Sql或实体框架查询中查找记录位置

Question

I'm trying to implement IBindingListView that will work with any Linq query as data source, but I'm stuck on the implementation of Find(PropertyDescriptor, Object) method which should find position of the record containg some value in specific property.

I don't want to iterate over all records in memory. I want database to do it.
Unfortunately Linq doesn't support row_number() SQL function and I'm unable to find any other way to do it while preserving ordering and filtering.

In other words:
Given

class Entity
{
   public string StringProperty {get; set;}
   public int IntProperty {get; set;}
   public string StringProperty2 {get; set;}
}

|StringProperty | IntProperty | StringProperty2|
|ccc            | 102         | value 2        |
|aaa            | 100         | value 0        |
|ddd            | 103         | value 3        |
|aaa            | 101         | value 1        |

and query

var query = from e in Entities
            where e.IntProperty > 100
            orderby e.StringProperty

Which gives me

|StringProperty | IntProperty | StringProperty2|
|bbb            | 101         | value 1        |
|ccc            | 102         | value 2        |
|ddd            | 103         | value 3        |

Find() with arguments StringProperty2 = 'value 2' should return 1 (0 based index), but it should be found using Linq so that it will be executed in database.

I don't have a problem if there will be 2 or 3 queries executed, but please don't assume I know anything about primary keys or specific Linq provider. We can assume that if Linq to SQL or Entity Framework is able to translate something to SQL than it can be used.

How can I implement IBindingListView.Find() method that works on any Linq query as a data source?

Answer 1

You can use lambda expression form for capture row data and row index. Example:

var query = youCollection
            .Select((r, i) => new {Row = r, Index = i});