Question

LINQ to SQL - 1 to many update / insert

Asked by: iziizi

I have created a simple blog which I am having some issues with. It saves OK, but updating causes an error:

"Server Error in '/' Application.
Violation of PRIMARY KEY constraint 'PK_Blog_CategoryMapping'. Cannot insert duplicate key in object 'dbo.Blog_CategoryMapping'."

I think this is because its trying to insert the same keys again instead of updating the keys.

Please see capture.png for a screen grab of my linq ORM.

See my code snip below for saving.

I think the problem is : be.BlogCategoryMappings.Add(bcm);

What I need to do is delete / update the mappings in CategoryMappings table, not try and insert them again. How is this done?

Thanks in advance

##SAVE METHOD##
public static void Save(int BlogID, string BlogTitle, string BlogText, DateTime BlogDate, bool Published, Guid AuthorID, bool Deleted,
                                                                bool AllowComments, string MetaTitle, string MetaDescription, string FriendlyURL, List<BlogCategoryMapping> bcml)
        {
            using (BlogDataContext db = new BlogDataContext())
            {
                BlogEntry be;
                bool IsNew = false;
 
                if (BlogID > 0)
                {
                    be = db.BlogEntries.Where(b => b.BlogID == BlogID).FirstOrDefault();
                }
                else
                {
                    be = new BlogEntry();
                    IsNew = true;
                }
 
                be.BlogTitle = BlogTitle;
                be.BlogText = BlogText;
                be.BlogDate = BlogDate;
                be.Published = Published;
                be.AuthorID = AuthorID;
                be.Deleted = Deleted;
                be.AllowComments = AllowComments;
                be.MetaTitle = MetaTitle;
                be.MetaDescription = MetaDescription;
                be.FriendlyURL = FriendlyURL;
 
                foreach (var i in bcml)
                {
                    BlogCategoryMapping bcm = new BlogCategoryMapping();
 
                    bcm.BlogID = i.BlogID;
                    bcm.CategoryID = i.CategoryID;
 
                    be.BlogCategoryMappings.Add(bcm);
                }
 
                if (IsNew)
                    db.BlogEntries.InsertOnSubmit(be);
 
                db.SubmitChanges();
 
                if (IsNew)
                    System.Web.HttpContext.Current.Response.Redirect("~/Administration/Blog.aspx?a=added&id=" + be.BlogID);
                else
                    System.Web.HttpContext.Current.Response.Redirect("~/Administration/Blog.aspx?id=" + be.BlogID);
                
            }
 
        }
                                  
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Asked On
2009-07-24 at 05:19:24ID24597652
Tags

LINQ

,

SQL

,

ASP.NET

,

Update

,

1 to many

Topics

Language Integrated Query - LINQ

,

C# Programming Language

,

.NET Framework 3.x versions

Participating Experts
1
Points
500
Comments
5

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Answers

 

by: iziiziPosted on 2009-07-24 at 08:11:27ID: 24935693

update:

If i change it so i first delete the mappings on an update as so:


                if (BlogID > 0)
                {
                    be = db.BlogEntries.Where(b => b.BlogID == BlogID).FirstOrDefault();
                }
                else
                {
                    be = new BlogEntry();
                    IsNew = true;
                }

Then it works. However this doesnt seem like the correct way of dealing with mappings. Can someone please shed some light?

 

by: iziiziPosted on 2009-07-24 at 08:12:09ID: 24935703

Sorry that should have read:

 if (BlogID > 0)
                {
                    be = db.BlogEntries.Where(b => b.BlogID == BlogID).FirstOrDefault();
                    db.ExecuteCommand("DELETE FROM Blog_CategoryMapping WHERE BlogID = " + BlogID);
                }
                else
                {
                    be = new BlogEntry();
                    IsNew = true;
                }

                                              
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by: FernandoSotoPosted on 2009-07-25 at 20:52:45ID: 24944110

Hi iziizi;

If the bcm.BlogID and bcm.CategoryID combination already exist in the BlogCategoryMapping table then do not attempt to added it again. These entries already exist so you must be modifying it. Once the records are in the tables there primary key will not change even when you edit them.

So this code should be done when you are mapping new entries from the tables and Not editing entries in the tables.
foreach (var i in bcml)
{
    BlogCategoryMapping bcm = new BlogCategoryMapping();

    bcm.BlogID = i.BlogID;
    bcm.CategoryID = i.CategoryID;

    be.BlogCategoryMappings.Add(bcm);
}

To your question, "What I need to do is delete / update the mappings in CategoryMappings table, not try and insert them again. How is this done?", If the records are already in the tables, BlogEntry and BlogCategory, and are already a member of the BlogCategoryMapping table then to modify the records in the tables BlogEntry or BlogCategory get a copy of the record from the database through your DataContext, change/modify the fields that need to be change and then do a db.SubmitChanges();. That is all that is needed to be done in an edit.

Fernando

 

by: iziiziPosted on 2009-07-26 at 01:56:20ID: 24944803

Hi Fernando,

Thanks for your reply.

"If the bcm.BlogID and bcm.CategoryID combination already exist in the BlogCategoryMapping table then do not attempt to added it again. These entries already exist so you must be modifying it. Once the records are in the tables there primary key will not change even when you edit them."

What happens if I want to remove a mapping? Do i not need to instruct it to be deleted?

 

by: FernandoSotoPosted on 2009-07-26 at 07:03:48ID: 24945814

Hi iziizi:;

To your question, "What happens if I want to remove a mapping? Do i not need to instruct it to be deleted?", Yes you do need to issue a command to delete an entry from the BlogCategoryMapping table. You will need both the BlogCategory and BlogEntry primary keys to do so because the entry in the BlogCategoryMapping table primary key is made up from both of these keys. See code snippet for a way to do this. Note that this will not delete any of the entries in the other two tables but just the BlogCategoryMapping table.

In the question title, "LINQ to SQL - 1 to many update / insert" The relationship between BlogCategory to BlogEntry is a Many to Many with the BlogCategoryMapping table being what is known as the junction table. So to insert records and do the mapping both BlogCategory and BlogEntry must exist before inserting into the BlogCategoryMapping table.

Fernando

public static void DeleteMapping(int blogId, int categoryId)
{
    using (BlogDataContext db = new BlogDataContext())
    {
        BlogCategoryMapping bcm = db.BlogCategoryMappings.Where(b =>
            b.BlogID == blogId && b.CategoryID == categoryId).Select(b => b).FirstOrDefault();
        db.BlogCategoryMappings.DeleteOnSubmit(bcm);
        db.SubmitChanges();
    }
}

                                              
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