Re: LINQ. Who knows how to do this?
- From: shapper <mdmoura@xxxxxxxxx>
- Date: Thu, 18 Oct 2007 05:08:03 -0700
On Oct 17, 8:06 pm, "Mark Dykun" <mdykun1...@xxxxxxxxxx> wrote:
Miguel,
In your database do you have relationships setup. When you create your LINQ
to SQL classes it uses the relationship data to determine the shape of the
objects. I created the 5 tables that you mentioned;
Post
File
Tag
PostTag
FileTag
I then setup the relationships inside if Enterprise manager. Created a LINQ
to SQL class including all of the tables. and then wrote the following
query;
LinqTestDbDataContext db = new LinqTestDbDataContext();
db.Log = Console.Out;
var values = from file in db.Files
select new { file.FileTag.Tag };
foreach (var value in values)
{
Console.WriteLine(value.Tag.TagID.ToString());
}
with the logging on I inspected the SQL that was created for execution
SELECT [t3].[test], [t3].[TagID], [t3].[TagDescription]
FROM [dbo].[File] AS [t0]
LEFT OUTER JOIN [dbo].[FileTag] AS [t1] ON [t1].[FileTagID] = [t0].[FileID]
LEFT OUTER JOIN (
SELECT 1 AS [test], [t2].[TagID], [t2].[TagDescription]
FROM [dbo].[Tag] AS [t2]
) AS [t3] ON [t3].[TagID] = [t1].[TagID]
As you can see it does work with Many-to-Many relationships. Just make sure
that you have relationships defined in the database.
Mark
"shapper" <mdmo...@xxxxxxxxx> wrote in message
news:1192622311.035968.298490@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Hello,
I created 3 few tables that have Many to Many relationships:
Posts (PostId PK)
Files (FileId PK)
PostsTags (PostId PK, TagId PK)
FilesTags (FileId PK, TagId PK)
Tags (TagId PK, TagName)
First of all, by dragging the tables to a dbml file the classes are
not ready for such Many to Many relationship:
Posts > PostsTags > Tags
and
Files > FilesTags > Tags
Does anyone knows how to do this?
And the behavior which seems logic to me (but maybe I am wrong) should
be:
(The example for Posts. For files is the same)
- When a tag is added to a Post, a record is added to TagsInPosts.
If the Tag (given its TagName) does not exist in Tags then it is
created in Tags table.
- When a tag is removed from a post then it is deleted from PostsTags.
If that tag is no longer associated with a Post or a File through
PostsTags and FilesTags then it is deleted from Tag.
Can I implement this logic in my LINQ classes or should I need to
create triggers, besides the constrains I enumerated, in my database?
I only find simple one-to-one examples and the only many-to-many
example is back to May 2006.
Thanks,
Miguel
Mark,
I am checking everything in my database and I will try again using
LINQ with Many to Many relationships.
Thanks,
Miguel
.
- References:
- LINQ. Who knows how to do this?
- From: shapper
- Re: LINQ. Who knows how to do this?
- From: Mark Dykun
- LINQ. Who knows how to do this?
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