Entity Framework Include with Func next

Un pattern şi trei implementări (partea 2)

Tudor Turcu - blog — Sun, 15 Nov 2009 14:27:50 GMT

După *** spuneam în postul precedent , fiecare O/RM are propria metodă de a descrie graful de obiecte

re: Entity Framework Include with Func next

Matthieu MEZIL — Sun, 08 Nov 2009 15:08:40 GMT

Try with DirectCast instead of TryCast. It was stupid in my case to use the as operator instead a direct cast.

re: Entity Framework Include with Func next

Ralf — Thu, 22 Oct 2009 08:50:48 GMT

Hello,

Thanks a lot for this code.

I was looking for something like that since I do not want to have strings for names sitting there too.

Now, I only have a strange problem: When I build a query and .Include it passes the data to the FuncToString routine as a ExpressionType.Convert (10) and not one of the three defined to work with.

I added another line to the case section, like this

Case ExpressionType.Convert

Return TryCast(TryCast(TryCast(selector, UnaryExpression).Operand, MemberExpression).Member, Reflection.PropertyInfo).Name (VB Syntax)

which is exactly the same as the .MemberAccess case except for another TryCase selector to UnaryExpression first.

I have no idea what I am doing there, how why what when, but it seems to work. Has anybody a hint why this change is needed, or what I was doing wrong in the first place? Why do I end up with ExpressionType Convert??

I have a second far harder question too: If you have two entities mapped m:n and the middle table of the database does not appear in your entity model (I like that...) I cannot get the function to work at all.

Any hint on that?

Thanks a lot!

Ralf

re: Entity Framework Include with Func next

Matthieu MEZIL — Thu, 17 Sep 2009 13:05:00 GMT

the problem with your solution is with collection : customers.Include("Orders.OrderDetails")

That's why I did it like this

Matthieu

re: Entity Framework Include with Func next

Kamil — Thu, 17 Sep 2009 12:53:59 GMT

I thinkk this is better:

public static ObjectQuery<T,K> Include<T>(this ObjectQuery<T> mainQuery, Expression<Func<T, K>> subSelector)

{

var sb = new StringBuilder();

FuncToString(sb, keyExpression.Body);

return mainQuery.Include(sb.ToString());

}

private static void FuncToString(StringBuilder sb, Expression selector)

{

switch (selector.NodeType)

{

case ExpressionType.Parameter:

// sb.Append(((ParameterExpression) selector).Name);

return;

case ExpressionType.MemberAccess:

FuncToString(sb, ((MemberExpression) selector).Expression);

sb.Append(".");

sb.Append(((MemberExpression) selector).Member.Name);

return;

}

throw new InvalidOperationException();

}

And now you can use like this:

query.Include(c=>c.Session)

.Incude(c=>c.Session.User)

re: Entity Framework Include with Func next

Matthieu MEZIL — Thu, 23 Jul 2009 20:47:12 GMT

Thanks a lot Diego

re: Entity Framework Include with Func next

Diego Vega — Thu, 23 Jul 2009 20:39:11 GMT

@Ken, I too wish we had addressed this in .NET 4.0, but unfortunately it didn’t climb to the top of the priority list as we were implementing other features (i.e. POCO support, functions exposed in LINQ, model defined functions, T4 integration, FK support, Contains, DefaultIfEmpty, Single/First/OrDefault, better stored procedure support, ExecuteStoreQuery/Translate, OrderBy Lifting, improvements for StartsWith, optimizations for non-unicode columns, EntityDataSource improvements including LINQ support, etc).

It is hard to get any new feature in for .NET 4.0 at this point, but I promise I will bring it up for the next version.

re: Entity Framework Include with Func next

Ken Smith — Wed, 22 Jul 2009 00:33:22 GMT

Very cool! I also hate using strings in this context: it seems counterintuitive, and very susceptible to mistakes. At the same time, I'm not sure I'll be using this method. Which of the following is easier for the next guy looking at my code to understand?

Room room = ctx.Room

.Include("Sessions.User")

.Include("Sessions.Whiteboards.Owner")

.Include("Sessions.Whiteboards.WhiteboardShape")

.Include("Sessions.MediaStreams")

.Include("Owner")

.FirstOrDefault(r => r.OwnerID == ownerUserID && r.Name == roomName);

Room room2 = ctx.Room

.Include(r => r.Sessions.Include<Session, User>(s => s.User))

.Include(r => r.Sessions.Include<Session, Whiteboard>(s => s.Whiteboards).Include<Whiteboard, User>(w => w.Owner))

.Include(r => r.Sessions.Include<Session, Whiteboard>(s => s.Whiteboards).Include<Whiteboard, WhiteboardShape>(w => w.WhiteboardShape))

.Include(r => r.Sessions.Include<Session, MediaStream>(s => s.MediaStreams))

.Include(r => r.Owner)

.FirstOrDefault(r => r.OwnerID == ownerUserID && r.Name == roomName);

They both do the same thing, but it requires a great deal more effort to understand what the second one is doing. I don't like the first way at all -- but the second way is, if anything, uglier and more complicated.

That's not to say I don't appreciate the code -- I very much do! You're trying to solve a problem that MS really should have solved itself. There just doesn't seem to be an easy way to solve it.

Does anyone know if MS has addressed this in .NET 4.0?

Entity Framework Include with Func

Jiří {x2} Činčura — Tue, 21 Apr 2009 21:49:01 GMT

Really good extension methods. msmvps.com/.../entityframework-include-with-func.aspx

re: Entity Framework Include with Func next

Matthieu MEZIL — Tue, 26 Aug 2008 19:09:06 GMT

Thanks

re: Entity Framework Include with Func next

Mike L — Tue, 26 Aug 2008 19:04:12 GMT

Absolutely incredible! I don't know what else to say