Living in the Tech Avalanche Generation

public interface ISpecification<T>
{
    Expression<Func<T, bool>> EvalPredicate { get; }
    Func<T, bool> EvalFunc { get; }
    bool Matches(T entity);
}

public void employees_from_uk()
{
    var all_employees_on_file =
        XDocument.Load(@"..\..\XML\Employees.xml").Descendants();

    Specification<XElement> aus_emp_spec =
        new Specification<XElement>
            (x => x.Attribute("Country").Value == "Australia");

    var aus_employees = from e in all_employees_on_file.Descendants()
                        .Where(aus_emp_spec.EvalFunc)
                        select e;

    aus_employees.ToList().ForEach(x =>
        { Console.WriteLine(x.ToString()); });
}

public void employees_from_uk_that_are_ceo()
{
    var all_employees_on_file =
        XDocument.Load(@"..\..\XML\Employees.xml").Descendants();

    var aus_emp_spec =
        new Specification<XElement>
            (x => x.Attribute("Country").Value == "UK");

    var ceo_emp_spec =
        new Specification<XElement>
            (x => x.Attribute("Title").Value == "CEO");

    var compound_spec = aus_emp_spec & ceo_emp_spec;

    var aus_employees = from e in all_employees_on_file.Descendants()
                        .Where(compound_spec.EvalFunc)
                        select e;

    aus_employees.ToList().ForEach(x =>
        { Console.WriteLine(x.ToString()); });
}

public void skip_while_employees_from_usa_then_return_the_rest_regardless()
{
    var all_employees_on_file =
        XDocument.Load(@"..\..\XML\Employees.xml").Descendants();

    var usa_empoyee_spec =
        new Specification<XElement>
            (x => x.Attribute("Country").Value == "USA");

    var usa_emps = from e in all_employees_on_file.Descendants()
                       .SkipWhile(usa_empoyee_spec.EvalFunc)
                       select e;

    usa_emps.ToList().ForEach(x =>
        { Console.WriteLine("Skipping from the USA : " +
            x.ToString()); });
}

public void customer_joined_with_customer_representative()
{
    var cust_rep_spec =
        new Specification<XElement>(x => x.Name == "CustomerRep");
    var emp_id_spec =
        new Specification<XAttribute>(x => x.Name == "EmployeeID");

    var all_employees_on_file =
        XDocument.Load(@"..\..\XML\Employees.xml").Descendants().Attributes();

    var all_customers_on_file =
        XDocument.Load(@"..\..\XML\Customers.xml").Root.Descendants().Elements();

    var customer_with_rep =
        from c in all_customers_on_file.Where(cust_rep_spec.EvalFunc)
        from e in all_employees_on_file.Where(emp_id_spec.EvalFunc)
        where c.Value == e.Value
        select new
        {
            c = c.Parent.Element("FirstName").Value + " " +
                c.Parent.Element("LastName").Value,
            e = e.Value
        };

    customer_with_rep.ToList().ForEach(x =>
    {
        Console.WriteLine(
            string.Format("Customer : {0} is represented by Rep Number {1}",
            x.c, x.e));
    });
}

 

For ease of reading this code without the necessity of downloading the code, I have included the XML directly in the post here.

 

 

<?xml version="1.0" encoding="utf-8" ?>
<Employees>
  <Employee EmployeeID="1" FirstName="Nancy"
            LastName="Davolio" Title="Sales Representative"
            HireDate="1992-05-01T00:00:00" Country="USA"
            Extension="5467" />
  <Employee EmployeeID="2" FirstName="Andrew"
            LastName="Fuller" Title="Vice President, Sales"
            HireDate="1992-08-14T00:00:00" Country="AUSTRALIA"
            Extension="3457" />
  <Employee EmployeeID="3" FirstName="Janet"
            LastName="Leverling" Title="Sales Representative"
            HireDate="1992-04-01T00:00:00" Country="USA"
            Extension="3355" />
  <Employee EmployeeID="4" FirstName="Margaret"
            LastName="Peacock" Title="Sales Representative"
            HireDate="1993-05-03T00:00:00" Country="AUSTRALIA"
            Extension="5176" />
  <Employee EmployeeID="5" FirstName="Steven" LastName="Buchanan"
            Title="Sales Manager" HireDate="1993-10-17T00:00:00"
            Country="UK" Extension="3453" />
  <Employee EmployeeID="6" FirstName="Michael"
            LastName="Suyama" Title="Sales Representative"
            HireDate="1993-10-17T00:00:00" Country="UK"
            Extension="428" />
  <Employee EmployeeID="7" FirstName="Robert" LastName="King"
            Title="CEO" HireDate="1994-01-02T00:00:00"
            Country="UK" Extension="465" />
  <Employee EmployeeID="8" FirstName="Laura" LastName="Callahan"
            Title="Inside Sales Coordinator"
            HireDate="1994-03-05T00:00:00" Country="USA"
            Extension="2344" />
  <Employee EmployeeID="9" FirstName="Anne" LastName="Dodsworth"
            Title="Sales Representative" HireDate="1994-11-15T00:00:00"
            Country="UK" Extension="452" />
</Employees>

<?xml version="1.0" encoding="utf-8" ?>
<Customers>
  <Customer>
    <FirstName>Simon</FirstName>
    <LastName>Segal</LastName>
    <JoinDate>19-10-2008</JoinDate>
    <Country>Australia</Country>
    <Email>simon.segal@techavalanche.com</Email>
    <MobilePhone>0405987367</MobilePhone>
    <CustomerRep>2</CustomerRep>
  </Customer>
  <Customer>
    <FirstName>Bob</FirstName>
    <LastName>Jones</LastName>
    <JoinDate>23-10-2008</JoinDate>
    <Country>Germany</Country>
    <Email>bob.j@bundes.com</Email>
    <MobilePhone>8983478347</MobilePhone>
    <CustomerRep>1</CustomerRep>
  </Customer>
  <Customer>
    <FirstName>Clair</FirstName>
    <LastName>Humgola</LastName>
    <JoinDate>10-10-2008</JoinDate>
    <Country>Australia</Country>
    <Email>chumg@telstra.com.au</Email>
    <MobilePhone>0458193487</MobilePhone>
    <CustomerRep>4</CustomerRep>
  </Customer>
  <Customer>
    <FirstName>Milton</FirstName>
    <LastName>Nomik</LastName>
    <JoinDate>20-12-2008</JoinDate>
    <Country>Australia</Country>
    <Email>milt.n@techavalanche.com</Email>
    <MobilePhone>09072625717</MobilePhone>
    <CustomerRep>6</CustomerRep>
  </Customer>
</Customers>

[LazyLoad("Customer", AttributeTargetMembers = @"regex:(Customer$)")]
[LazyLoad("Order_Details", AttributeTargetMembers = @"regex:(Order_Details$)")]
public partial class Order : IFetchable
{
    private IFetchingStrategy _strategy;
    public IFetchingStrategy FetchingStrategy
    {
        get { return _strategy; }
        set { _strategy = value; }
    }
}

Note that this attribute is already written and part of the code download, you don’t have to write any PostSharp attributes yourself to get the code to work. Once having applied the attribute and compiled, PostSharp kicks in and weaves code where it’s directed, in this case the Order entities Customer and Order_Details properties. A look at the code in Reflector confirms this:

Now cool as PostSharp is, this is not a job I was hoping to have to have ever used it for. Entity Framework shouldn’t need that much work for transparent lazy loading and we are promised that will change in a later (next?) version. The lazy loading however is only part of the story. As much as I want transparent Lazy Loading OOTB, I equally need the Eager Loading story to be dealt with. As I have said throughout this series of posts, part of the fetching strategy problem lies in the disconnect between Lazy and Eager fetching and something tells that I will still be rewriting this solution for a later version of Entity Framework.

This solution isn’t proven in battle and needs a lot more work to verify it’s bona fides, but I will push it forward on very small, low risk projects to see how it pans out. I for one really want the Entity Framework to ‘make good’ and reach the hearts and minds of the POCO and DDD audience into the bargain. The question is how long am I prepared to wait and ‘go via the cape’?