亚音速-将linq查询转换为sql查询/ DataReader

Question

Let's say I have a the following query:

int x = 5;
var result = from p in db.products
             where p.CategoryId == x
             select p;

int count = result.Count();
List<product> products = result.ToList();

That's what I have now. But aditionally I need to have a DataReader from result:

// that's what I need:
var reader = ConvertSubSonicLinqQueryToDataReader(result);

How can I convert the linq statement to something I can work with? A DataReader or a DbCommand or even plain sql with a list of paramters.

I know SubSonic can do that (since it translates the query to plain sql anyway) but I haven't found anything in the public accessible methods yet.

Any suggestions?

Answer 1

Converting the LINQ query is the wrong approach. LINQ returns results at a level of abstraction higher than a DataReader works at.

There's also the issue of deferred execution so your LINQ query may not be executed as a single SQL statement anyway.

Rater than use a LINQ statement why not just use an SqlQuery instead?

var qry = new Select().From(Product.Schema).Where(Product.CategoryIdColumn).IsEqualTo(x);

return qry.ExecuteReader();

Edit:
Just seen you're using SubSonic3 (not 2 as the above code would be for) but the potential misuse of LINQ and duplication of work still stands.

Answer 2

The code that creates object from the DataReader can be found in DbDataProvider.ToEnumerable. It's called from DbQueryProvider's Execute method (line 227). The best way to "understand" the LINQ magic is to place some breakpoints on DbQueryProvider methods.