ASP.NET Linq help
- Thread starter Izi
- Start date
If you set them both as primary keys linq will remove the table from the diagram and just show a direct mapping... incase you dont know
I have set them both as primary keys....
They now show in the intellisense which wasnt happening before is that what you mean?
Also I have another question, this one a little more complicated.
I have a static member which retrieves a blog entry:
Code:
public static BlogEntry GetBlogEntry(int id)
{
using (BlogDataContext db = new BlogDataContext())
{
return db.BlogEntries.Where(b => b.BlogID == id).FirstOrDefault();
}
}This works fine.
I then have this code to save a new record, or update a record:
Code:
DateTime ds = Helper.BuildDateTime(txtDate.Text, TimePicker1.GetTextHour.ToString(), TimePicker1.GetTextMin.ToString(), TimePicker1.GetTextSecond.ToString());
BlogEntry be;
bool IsNew = false;
be = Blog.GetBlogEntry(Helper.QueryStringInt("id"));
if (be == null)
{
IsNew = true;
be = new BlogEntry();
}
if (Helper.QueryStringInt("id") >= 1)
be.BlogID = Helper.QueryStringInt("id");
be.BlogTitle = txtTitle.Text;
be.BlogText = txtContent.Text;
be.BlogDate = ds;
be.Deleted = false;
be.Published = chkPublish.Checked;
be.AllowComments = chkComments.Checked;
be.FriendlyURL = txtFriendlyURL.Text;
be.MetaDescription = txtMetaDescription.Text;
be.MetaTitle = txtMetaTitle.Text;
foreach (ListItem li in chkCategories.Items)
{
BlogCategoryMapping bcm = new BlogCategoryMapping();
bcm.BlogID = be.BlogID;
bcm.CategoryID = Convert.ToInt32(li.Value);
be.BlogCategoryMappings.Add(bcm);
}
BlogDataContext db = new BlogDataContext();
if (IsNew)
db.BlogEntries.InsertOnSubmit(be);
db.SubmitChanges();
db.Dispose();Now this works fine for adding, however editing doesnt. THe reason for this is this line:
Code:
be = Blog.GetBlogEntry(Helper.QueryStringInt("id"));To get it working I have to get the blog entry with in the context scope set in the save method like so:
Code:
DateTime ds = Helper.BuildDateTime(txtDate.Text, TimePicker1.GetTextHour.ToString(), TimePicker1.GetTextMin.ToString(), TimePicker1.GetTextSecond.ToString());
BlogEntry be;
bool IsNew = false;
BlogDataContext db = new BlogDataContext();
be = db.BlogEntries.Where(b => b.BlogID == id).FirstOrDefault();
if (be == null)
{
IsNew = true;
be = new BlogEntry();
}
if (Helper.QueryStringInt("id") >= 1)
be.BlogID = Helper.QueryStringInt("id");
be.BlogTitle = txtTitle.Text;
be.BlogText = txtContent.Text;
be.BlogDate = ds;
be.Deleted = false;
be.Published = chkPublish.Checked;
be.AllowComments = chkComments.Checked;
be.FriendlyURL = txtFriendlyURL.Text;
be.MetaDescription = txtMetaDescription.Text;
be.MetaTitle = txtMetaTitle.Text;
foreach (ListItem li in chkCategories.Items)
{
BlogCategoryMapping bcm = new BlogCategoryMapping();
bcm.BlogID = be.BlogID;
bcm.CategoryID = Convert.ToInt32(li.Value);
be.BlogCategoryMappings.Add(bcm);
}
if (IsNew)
db.BlogEntries.InsertOnSubmit(be);
db.SubmitChanges();
db.Dispose();Why is this?
What I mean is that when you look at one objects properties, you shouldn't have go to through the linking table (i.e. it will looke like BlogEntry -> BlogCategory rather than BlogEntry -> MappingTable -> BlogCategory). If done correctly the mapping table does not appear on the DataContext at all - its all implicit.
Unfortunately, all of the object update tracking is handled by the datacontext, so when you use your method GetBlogEntry, the datacontext that tracks that object changes is destroyed straight away. There is a method to attach an entity back to a data context but that doesn't seem to work.
Read: http://www.west-wind.com/weblog/posts/246222.aspx this explains the situation in more detail. I'm not 100% sure, but I think the Entity Framework (which is similar to Linq2SQL, but a bit less lightweight and the touted future of .Net data access) solves this issue (but not 100% sure!).
Hi Goksly,
Thanks for that. Unfortunatly this isnt happing. How should I go about this? with the above diagram?
Thanks.
Firstly, the mapping table has to just be 2 columns... you can't have a primary key and then the 2 columns. Make them both primary keys (composite key). Then remove the 3 tables from your context, referesh server explorer and try again. When you drop the three of them on, only 2 should appear.
The one that got me when I was doing it was the fact it must be just 2 columns.
The one that got me when I was doing it was the fact it must be just 2 columns.
Hmm, my ORM still shows all three! Is this correct:
The above is my database diagram, not my ORM
Last edited: