CODEWITHSUNDEEP
c#linqweb-services.net-3.5
Geoff Dalgas
Geoff Dalgas

Reputation: 6176

Filling a DataSet or a DataTable from a LINQ query result set

How do you expose a LINQ query as an ASMX web service?
Usually, from the business tier, I can return a typed DataSet or a DataTable which can be serialized for transport over ASMX.

How can I do the same for a LINQ query?
Is there a way to populate a typed DataSet or a DataTable via a LINQ query?

public static MyDataTable CallMySproc()
{
    string conn = "...";

    MyDatabaseDataContext db = new MyDatabaseDataContext(conn);
    MyDataTable dt = new MyDataTable();

    // execute a sproc via LINQ
    var query = from dr
                in db.MySproc().AsEnumerable
                select dr;

    // copy LINQ query resultset into a DataTable -this does not work !    
    dt = query.CopyToDataTable();
   
    return dt;
}

How could I put the result set of a LINQ query into a DataSet or a DataTable?
Alternatively, can the LINQ query be serializable so that I can expose it as an ASMX web service?

Upvotes: 159

Views: 88842

Answers (7)

Vijay S
Vijay S

Reputation: 292

If you use IEnumerable as the return type, it will return your query variable directly.

MyDataContext db = new MyDataContext();
IEnumerable<DataRow> query = 
    (from order in db.Orders.AsEnumerable()
        select new
        {
            order.Property,
            order.Property2
        })
    as IEnumerable<DataRow>;
return query.CopyToDataTable<DataRow>();

Upvotes: 6

Gabriel Magana
Gabriel Magana

Reputation: 4536

For the sake of completeness, these solutions do not work for EF Core (at least not for EF Core 2.2). Casting to IEnumerable<DataRow>, as suggested in the other answers here, fails. Implementing this class and extension methods worked for me https://learn.microsoft.com/en-us/dotnet/framework/data/adonet/implement-copytodatatable-where-type-not-a-datarow.

Why it's not built into EF Core, I have not idea.

Upvotes: 3

Daniel Flippance
Daniel Flippance

Reputation:

To perform this query against a DataContext class, you'll need to do the following:

MyDataContext db = new MyDataContext();
IEnumerable<DataRow> query = 
    (from order in db.Orders.AsEnumerable()
        select new
        {
            order.Property,
            order.Property2
        })
    as IEnumerable<DataRow>;
return query.CopyToDataTable<DataRow>();

Without the as IEnumerable<DataRow>; you will see the following compilation error:

Cannot implicitly convert type 'System.Collections.Generic.IEnumerable' to 'System.Collections.Generic.IEnumerable'. An explicit conversion exists (are you missing a cast?)

Upvotes: 32

Brian Childress
Brian Childress

Reputation: 1158

Create a class object and return a list(T) of the query.

Upvotes: 15

Jon Galloway
Jon Galloway

Reputation: 53125

As mentioned in the question, IEnumerable has a CopyToDataTable method:

IEnumerable<DataRow> query =
    from order in orders.AsEnumerable()
    where order.Field<DateTime>("OrderDate") > new DateTime(2001, 8, 1)
    select order;

// Create a table from the query.
DataTable boundTable = query.CopyToDataTable<DataRow>();

Why won't that work for you?

Upvotes: 99

Dave Ward
Dave Ward

Reputation: 60580

If you use a return type of IEnumerable, you can return your query variable directly.

Upvotes: 19

Lars M&#230;hlum
Lars M&#230;hlum

Reputation: 6102

Make a set of Data Transfer Objects, a couple of mappers, and return that via the .asmx.
You should never expose the database objects directly, as a change in the procedure schema will propagate to the web service consumer without you noticing it.

Upvotes: 25

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