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Hello !
I'm using Entity Framework6 with VB.net and SQL server 2008R2.
I have this case :
This is my model :
Partial Public Class Myobj
Public Property id As Integer
Public property name as string
Public Overridable Property chld As ICollection(Of chld) = New HashSet(Of chld)
End Class
Partial Public Class Myobj
Public shared cond1 as DateTime
<NotMapped> Public ReadOnly Property vls As integer
Get
Return chld.AsQueryable.Where(Function(t2) t2.date1<cond1).Select(Function(t3) t3.quantity).DefaultIfEmpty.Sum()
End Get
End Property
End Class
Partial Public Class chld
Public Property id As Integer
Public Property date1 as DateTime
Public Property quantity as Integer
Public Property ParentID as integer
Public Overridable Property MyObj1 As MyObj
End Class
Now on my form, I have this code :
Dim dt1 as DateTime=CDate("08/08/2014")
Myobj.cond1=dt1
Dim list1 = (From t In context.MyObj Select New With { _
.Parent = t, _
.chl = (From t2 In t.chld.AsQueryable.Where(Function(t3) t3.Date1>=dt1) Select t2)
}).ToList
This query always produces 0 in vls property for each item in Myobj1.( !! but it's not true according to data in database!!).
Why this query product a such result?
Thank you!
modified 20-Feb-15 15:38pm.
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You have to .Include(related) the related tables if you want the related objects rehydrated in EF.
Discussed here[^]
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Sorry , but what I should to include ?
If you can see , each Myobj1 object has a Calculated property vls that have a query that calculate the sum
Why should I include these ? I don't want to read from database the child's items before the date 08/08/2014 , but I want to get only the quantity's sum.
and if the query inside the partial class will be a normal query outside the class , will be work as expected without including nothing.
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It's because all of your child objects are null. They don't get re-hydrated unless they are listed in an Include on the original query.
That's why you're getting 0's in the calculated field. There is nothing to run any calculations on!
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In my main query , the first part is :
Dim list1 = (From t In context.MyObj Select New With { _
.Parent = t, _
In this moment , one of the property in"t" is vls. And this property get the value form that query inside the partial class. This query doesn't get executed ?
and why this is working ok :
Dim dt1 as DateTime=CDate("08/08/2014")
Myobj.cond1=dt1
Dim list1 = (From t In context.MyObj Select New With { _
.Parent = t, _
.chl = (From t2 In t.chld.AsQueryable.Where(Function(t3) t3.Date1>=dt1) Select t2)
.sum1 =(From t2 in t.chld.AsQueryable.Where(Function(t2) t2.date1<cond1).Select(Function(t3) t3.quantity).DefaultIfEmpty
}).ToList
In this case the sum1 results are ok ( as you can see it's the same query as inside the partial class )
The vls property inside the partial class have the same query.
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The concept is called "deferred execution". Your query isn't actually run until the code gets to the call to .ToList().
The reason why the vls property is 0 is because your property getter is not part of the query that re-hydrates the objects. That code isn't run until you call the property from some other code. I already told you why that property is returning 0. Because the objects it's working with don't exist yet.
Your original query never re-hydrated the chld objects, so the vls property didn't have anything to work with. That's why you need the .Includes().
It works if the code is part of the query because it gets baked into the SQL that is sent to the database. Again, you can SEE THIS by following the technique I told you about before. Get the SQL SELECT statement and paste it into a query window or into Notepad and READ IT.
Do you actually read any of the links we post? They would help you to understand what's going on in EF because you don't seem to have a grasp of it yet. Seriously, before you waste a ton of time whould why things are working, pickup the Programming Entity Framework and/or the Code First books by Julie Lerman and read them.
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Thank you !
But can you get me a suggestion how resolve the situation ?
Is there any method to put those sum in the Calculated property ?
Actually , I try to run like this :
Dim dt1 as DateTime=CDate("08/08/2014")
Dim list1 = (From t In context.MyObj Select New With { _
.Parent = t, _
.chl = (From t2 In t.chld.AsQueryable.Where(Function(t3) t3.Date1>=dt1) Select t2)
.sum1 =(From t2 in t.chld.AsQueryable.Where(Function(t2) t2.date1<dt1).Select(Function(t3) t3.quantity).DefaultIfEmpty
}).ToList
and after :
For Each l In list1
l.Parent.vls=l.sum1
Next
But this is executed very slow.
Is there any better method ?
Thank you !
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I already told you what to do. I gave you a link that shows you how to do it. I've even told you why your code doesn't work.
Dim list1 = (From t in context.MyObject.Include("chld") Select New ...
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Yes , but I think you don't understand that I don't want to include all the childs.
For the childs with date before 08/08/2014 I want to get only the quantity's sum.
The childs with date after 08/08/2014 I want to include.
The code that I write in my last post , do what I want , but the part " From each...... run very slow.
Do you know a better solution ?
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You have a choice. You can either
1) The slow way. Do the calculation in your property getter where you have to wait for EF to re-hydrate all the related child objects into memory and then your getter code applies its filter and does the calculation.
Or
2) You drop the property getter code and move the filtering to the query and let the database filter the child objects and do the math for you. Something the database engine was designed to do very well.
The choice is up to you.
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Thank you !.
The problem is that for some reasons I need to have the sum values in a Myobj's property.
Do you think that is possible that I can realize your second variant with my above condition ?
Thank you !
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Ho many minutes would it take you to TRY IT?
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the problem is I don't know how ?
Could you explain how can I do ?
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I ALREADY HAVE! MULTIPLE TIMES! Go back and re-read these posts!
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Quote: You have a choice. You can either
1) The slow way. Do the calculation in your property getter where you have to wait for EF to re-hydrate all the related child objects into memory and then your getter code applies its filter and does the calculation.
Or
2) You drop the property getter code and move the filtering to the query and let the database filter the child objects and do the math for you. Something the database engine was designed to do very well.
Can you explain how to do the second ?
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yes , but after these instructions , I need to put those sums in the .vls .
and to do this I know only this way :
For Each l In list1
l.Parent.vls=l.sum1
Next
But as I wrote in one of my previous messages this is too slow
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I told you you can't do what you want to do and get the speed out of it. It just isn't possible.
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Quote: You have a choice. You can either
1) The slow way. Do the calculation in your property getter where you have to wait for EF to re-hydrate all the related child objects into memory and then your getter code applies its filter and does the calculation.
Or
2) You drop the property getter code and move the filtering to the query and let the database filter the child objects and do the math for you. Something the database engine was designed to do very well.
The choice is up to you.
Yes but you call the first way as "slow way" an not the second. Why the second is slow ?
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Dude. I don't have your database. I don't know what your overall objective is. I don't know what you're reasons are for anything and you've put up so many code snippets, I have no idea what you're referring to or what you're referring to when you say "slow". Without that stuff, I'm at a severe disadvantage in diagnosing your problems.
YOU have to understand how EF works and you're not going to get that information from a few forum posts. I already told you, pick up a book on EF and Code First and work through them.
I've already told you why your queries are returning 0's for values, but you don't seems to get it and you don't seem to understand the limitations of your design or of EF.
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Hello Friend ! ( not dude ! )
You don't have my database , but you have my EF model from my first post.
And as you have a lot's of experience , you can imagine how the database is.
Anyway , my last question was not for database , but for a simple In memory For.. each loop that run slow.
And I think it's not good to tell a someone " You have asked about this , ok take these books and read" .
Then why this forum is still open , replace your webpage with a big poster :
You that have problems with Entity ------ Read this book
You that have problems with C# ------------ Read this book.
.......
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dilkonika wrote: You don't have my database , but you have my EF model from my first post.
Model, yes. Data, no.
dilkonika wrote: Anyway , my last question was not for database , but for a simple In memory For.. each loop that run slow.
Oh, but it IS about your database. You just refuse to listen to why when I've told you time and time again. Your data is NOT in memory!! You have a proxy object that EF must go back to requery the data for and that's why it's so slow! That's why I keep telling you to use an Include to get the child elements into memory! That's why I keep telling you to pick up a book on EF so you understand all of these little details you don't understand about EF, such a "deferred execution" and "lazy loading"!
dilkonika wrote: You that have problems with Entity ------ Read this book
You that have problems with C# ------------ Read this book.
There's simply too much information to cover in a few forum posts! Forums can NOT answer all questions because forum posts can NOT convey all of the little details of an answer in the limited space available to us. If we could... if we did that we'd all be writing entire book chapters for forum posts! 
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Dim dt1 as DateTime=CDate("08/08/2014")
Dim list1 = (From t In context.MyObj Select New With { _
.Parent = t, _
.chl = (From t2 In t.chld.AsQueryable.Where(Function(t3) t3.Date1>=dt1) Select t2)
.sum1 =(From t2 in t.chld.AsQueryable.Where(Function(t2) t2.date1<dt1).Select(Function(t3) t3.quantity).DefaultIfEmpty
}).ToList
and after :
For Each l In list1
l.Parent.vls=l.sum1
Next
After the Tolist , all List1's : .Parent , .chl , .sum1 are in memory ? (That's the book's say about the .ToList , or show me an article that say the opposite ).
So now the following , For...each is run on memory ? Or I'm wrong ?
Thank you !
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Hello !
This is my last question :
I don't know why , but this is working :
Partial Public Class Myobj
Public Property id As Integer
Public property name as string
Public Overridable Property chld As ICollection(Of chld) = New HashSet(Of chld)
End Class
Partial Public Class Myobj
<NotMapped> Public Property vls As integer
End Class
Partial Public Class chld
Public Property id As Integer
Public Property date1 as DateTime
Public Property quantity as Integer
Public Property ParentID as integer
Public Overridable Property MyObj1 As MyObj
End Class
Public Class PseudoMyObj
Inherits MyObj
End Class
Now on my form, I have this code :
Dim dt1 as DateTime=CDate("08/08/2014")
Dim list1 = (From t In context.MyObj Select New With { _
.Parent = New PseudoMyObj With { _
.chld = (From t2 in t.chld.AsQueryable.Where(Function(t3) t3.Date1>=dt1) Select t2), _
.vls=(t.chld.AsQueryable.Where(Function(t2) t2.date1<dt1).Select(Function(t3) t3.quantity).DefaultIfEmpty.Sum()) _
}).ToList
dim mylist as IEnumerable(of MyObj)=list1.Select(Function(t2) t2.Parent)
Please , I want your opinion , do you see anything wrong with this code ?
Thank you !
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I already told you why it works. Your first query, and the sub-queries, on the database engine.
Getting the SQL query statement from the debugger and examining it in Notepad or in SQL Server Manager would have told you that.
Your second query, the last statement in your post, is executed client-side, not on the database engine.
I'm not telling you these things, like the above technique, because I like hearing myself type this crap. I tell you these things because this is how I debug and examine the functionality of EF.
Have a nice life.
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