如何从表格中仅获得一列？

Question

i have a table named "table_1" which contains id, col_1, col_2, col_3. col_1 is the summary property, so, when i query "table_1" (by any filter), i get the query result summarized by the summary property "col_1".

I need to get the same result but summarized by "col_2" that isn't the summary property. Can anyone help me?

Here's my query code:

partial void table_1_PreprocessQuery(ref IQueryable<table_1Item> query)
{
    query = (from item in query
    select item.col_2).Execute().Distinct();
}

It doesn't work because it throw me an exception like this:

"Cannot implicitly convert type 'System.Linq.IQueryable in System.Linq.IQueryable"

col_2 is a string type. So i need that the query result type is System.Linq.IQueryable<table_1Item> .

Answer 1

change

partial void table_1_PreprocessQuery(ref IQueryable<table_1Item> query)
    {
        query = (from item in query
                 select item.col_2).Execute().Distinct();
    }

to

partial void table_1_PreprocessQuery(ref IQueryable<table_1Item> query)
    {
        query = (IQueryable<table_1Item>)(from item in query
                 select item.col_2).Execute().Distinct();
    }

This will cast explicitly.