Solved

Entity Framework doesn't update Many to Many relation

Posted on 2013-06-18
10
442 Views
Last Modified: 2013-06-20
Hi Experts,

I have the following tables in an SQL2008 database:

Accommodation
code	varchar(18)
name	varchar(80)

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This table has more columns but i have removed them here for simplicity.

Attributes
code	int
name	varchar(50)

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AccommodationAttributes
AccommodationCode	varchar(18)
AttributeCode	int

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As you may get, AccommodationAttributes describes the many to many relationship between Accommodations and Attributes.

I have created my model (EF5) using database first, and it has created two classes linked with a navigation property.

All this seems correct.

What i am trying to do is add values in the db, but though i am able to add Accommodations and Attributes, i don't seem to be able to make it add the corresponding values in the AccommodationAttributes table.

I am reading from an XML file.
Bellow is a code sample of what i am trying to do.

var Accommodations = from a in xe.Elements("accommodation") select a;
foreach (var accommodation in Accommodations)
{
   var AccCode = accommodation.Element("code").Value;
   Accommodation a = context.Accommodations.Where(x=>x.code == AccCode).SingleOrDefault();
   bool newAccommodation = a == null ? true : false;
   a = !newAccommodation ? a :
      new Accommodation
      {
          code = accommodation.Element("code") == null ? null : accommodation.Element("code").Value,
          name = accommodation.Element("name") == null ? null : accommodation.Element("name").Value
      };
      foreach (var attribute in accommodation.Elements("attributes").Elements("attribute").Select(x=>x.Value))
      {
         Attribute at = context.Attributes.Where(x => x.name == attribute).SingleOrDefault();
         a.Attributes.Add(at);
      }
      context.SaveChanges();
}

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After running this code i Run the following in SQL:
select COUNT(*) from Accommodations
select COUNT(*)from Attributes
select COUNT(*)from AccommodationAttributes

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But though i see entries in the two tables, the link table comes with 0 rows.

I have tried other variations, like attaching the objects to the context, or implicitly specifying that it is a modified object.

By the time that this code will run i am sure that the Attributes are allready inserted in the db, but the Accommodation is either an Insert or Update.

I am eager to hear your thoughts,

Giannis
0
Comment
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10 Comments
 
LVL 15

Accepted Solution

by:
jorge_toriz earned 500 total points
Comment Utility
I did it with this code and everything worked so fine :s

EFModel.ExpertsExchangeEntities db = new EFModel.ExpertsExchangeEntities();
EFModel.Accommodation myAccommodation = new EFModel.Accommodation();
myAccommodation.Code = "Acc01";
myAccommodation.Name = "Accommodation 01";

myAccommodation.Attributes.Add(new EFModel.Attribute()
{
    Code = 1,
    Name = "Attribute 1"
});

myAccommodation.Attributes.Add(new EFModel.Attribute()
{
    Code = 2,
    Name = "Attribute 2"
});

db.AddToAccommodations(myAccommodation);

db.SaveChanges();

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0
 
LVL 23

Author Comment

by:Ioannis Paraskevopoulos
Comment Utility
Hi,

Thanks for the response...
Can you please elaborate a little bit?

Is db the context in my example?
I don't have a method AddToAccommodations.

Giannis
0
 
LVL 15

Expert Comment

by:jorge_toriz
Comment Utility
your "context" variable is my "db" variable, the method AddToAccommodations was generated by the Entity Framework wizard.

I'm attaching the project in this reply.

I renamed the file EFModel\EE.edmx to EFModel\EE.txt to be able to send you the project in the zip, just fix the extension and the project should run without problems.
Project.zip
0
 
LVL 23

Author Comment

by:Ioannis Paraskevopoulos
Comment Utility
Hi,

I do see that in your project. One question, is that EF4? I am using EF5.

Giannis
0
 
LVL 15

Expert Comment

by:jorge_toriz
Comment Utility
Yes, I'm working with 4 :s
0
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LVL 23

Author Comment

by:Ioannis Paraskevopoulos
Comment Utility
Is it possible that EF4 is somewhat different from EF5 in that manner?
0
 
LVL 15

Expert Comment

by:jorge_toriz
Comment Utility
I'm really sorry pal, I haven't worked on EF5, but let me search something about many to may relationships in EF5 and verify if there is something different that you must take care of
0
 
LVL 23

Author Comment

by:Ioannis Paraskevopoulos
Comment Utility
Hi,

After further investigation, it seems that it works when i add a new Accommodation, but it fails when the Accommodation is already in the db and i just add new attributes. In my case in the process of developing i had first added the Accommodation and in a later step of development i created the process to import attributes. So i need to find a way to update the relationship when both accommodation and  attribute are already in the db. Thanks for the help.

Giannis
0
 
LVL 23

Author Comment

by:Ioannis Paraskevopoulos
Comment Utility
I found the solution...The problem was i had set the AutoDetectChangesEnabled to False. When i commented out this line it worked. I am marking the answer as accepted because it was correct in its core and the expert could not know my settings due to information provided.

Thanks a lot for the help, even indirectly it helped me get the solution i needed.

Giannis
0
 
LVL 23

Author Closing Comment

by:Ioannis Paraskevopoulos
Comment Utility
Thanks a lot for your help and patience.

Giannis
0

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