How to create a complex type from a stored procedure that uses exec()?

Question

I want to create a complex type to use within an entity manager from a query constructed dynamically and executed with exec(). Is it possible?; since I'm writing a filter, what would you do instead if it is not possible?

Also, I'm evaluating using linq, but the filter needs many tables and their registers, therefore efficiency is a concern.

Thanks...

Answer 1

Yes, you can use Entity Framework 4 and LINQ on top, it generates the parametrized query and executes it, that's the option.

Another option is (and I did several times) to create a base class/interface, let's say:

public interface IExecutable
{
    void Execute(IConnection connection);
}
public interface IExecutable<TResult> : IExecutable
{
    TResult Result { get; }
}

public abstract ActionBase<TResult> : IExecutable<TResult>
{
    protected void AddParameter(....);

    protected IDataReader ExecuteAsReader(string query) {
        //create a DB Command, open transaction if needed, execute query, return a reader.
    }

    protected object ExecuteAsScalar(string query) {
        //....
    }

    //the concrete implementation
    protected abstract TResult ExecuteInternal();

    IExecutable.Execute(IConnection connection) {
        //keep the connection
        this.Result = ExecuteInternal();
    }

    //another common logic: 

}

Then you can create your concrete actions:

public sealed class GetUsersAction : ActionBase<<IList<User>>
{
    //just a constructor, you provide it with all the information it neads
    //to be able to generate a correct SQL for this specific situation
    public GetUsersAction(int departmentId) {
        AddParameter("@depId", departmentId);
    }

    protected override IList<User> ExecuteInternal() {
        var command = GenerateYourSqlCommand();

        using(var reader = ExecuteAsReader(command)) {
            while(reader.Read) {
                //create your users from reader
            }
        }
        //return users you have created
    }
}

Very easy to create concrete actions!

Then, to make it even easier, create an ExecutionManager whose concern is how to get the connection and execute the action:

public sealed ExecutionManager() {

    TResult Execute<TResult>(IExecutable<TResult> action) {
        var connection = OhOnlyIKnowHowTOGetTheConnectionAnfHereItIs();
        action.Execute(connection);
        return action.Result;
    }
}

Now just use it:

var getUsersAction = new GetUsersAction(salesDepartmentId);

//it is not necessary to be a singletone, up to you
var users = ExecutionManager.Instance.Execute(getUsersAction);

//OR, if you think it is not up to ExecutionManager to know about the results:
ExecutionManager.Instance.Execute(getUsersAction);
var users = getUsersAction.Result

Using this simple technique it is really easy to move all the connection/command/execution logic away from the concrete actions into the base class, and the concrete actions' concerns are just generating SQLs and converting database output into some meaningful results.

Good luck :)

Answer 2

If you decide to go the Linq route and are looking for a good way to do filtering. LinqKit is a great library for building ad-hoc predicates. The problem with the built-in linq library is that you can only ad-hoc combine AND statements, you can not ad-hoc combine OR statements. Linqkit makes that a breeze to accomplish.