Codepolice.net » SQL

IN queries with LINQ to SQL

Ola — Tue, 01 Jun 2010 13:33:12 +0000

This is another awesome feature in LINQ to SQL that i always forget about. Sometimes you have an array of strings or any other type and want to query the database for all values that have one of the values in the array.

string platform = "windows|linux";
string[] platformList = platform.Split('|');
itemQuery = from m in itemQuery
from p in m.PlattformItemRelations
where platformList.Contains(p.Plattform.Text.ToLower())
select m;

Ain’t that a beauty? I got this tip from Ron Connery so all the kudos to him.

Return random rows from a MS SQL database

Ola — Tue, 17 Nov 2009 12:13:36 +0000

I always forget this command:

SELECT * FROM YourTable TABLESAMPLE SYSTEM (10 PERCENT)

This gives you some sample data from your database. In this case 10 percent of the content. You could also use TABLESAMPLE SYSTEM (1000 ROWS) to get 1000 sample rows. Great to use if you have a big database and do not want the same data again and again when you debug or something.

SQL Server: Saving changes is not permitted because table will be re-created

Ola — Thu, 10 Sep 2009 09:52:35 +0000

Microsoft has added a setting to Management Studio to prevent us from re-create tables when we make changes to them. I don’t like this settings and it would have be much better if they said ‘This table will be re-created, are you sure you want to do that?” instead of just stop us from doing it.

There is an option to turn this off if you go to “Tools -> Options -> Designers -> Table and Database Designers” and the uncheck the checkbox “Prevent saving changes that require table re-creation”.

ASP.NET membership: System.Web.Security. SqlRoleProvider problems

Ola — Tue, 16 Dec 2008 21:18:46 +0000

I had this really weird problem just now. I have done some work with the ASP.NET Membership provider and everything has been working great. But when i tried to deploy my application to the server i got this:

The ‘System.Web.Security.SqlRoleProvider’ requires a database schema compatible with schema version ’1′. However, the current database schema is not compatible with this version. You may need to either install a compatible schema with aspnet_reqsql.exe (available in the framework installation directory), or upgrade the provider to a newer version.

Alright, my database was exactly the same and everything looked fine. I tried to recreate my database with the aspnet_regsql.exe tool but nothing worked. Then i finally found this thread on the MSDN messageboard and one guy said that he gave his application a name in the aspnet_Applications table and put that name in the web.config like this.

connectionStringName="ApplicationServices"
applicationName="APPLICATION NAME"
name="AspNetSqlRoleProvider"
type="System.Web.Security.SqlRoleProvider, System.Web, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />

And that solved it. Really really strange and i have no idea if this is a bug or whatever. On my local machine (Vista with IIS7) it worked great to have a application named “/” but on my production machin (a Server 2003 with IIS6) it did not.

Now i should stop working for today.

Join and Group By with LINQ to Entities

Ola — Tue, 25 Nov 2008 15:21:55 +0000

I have banged my head against some LINQ to Entities stuff today. It started out when i was doing a query to get some stats out of my forum. I should point out that i’m a newbe with LINQ to Entities and the Entity Framework so if i have done anything stupid here you are free to mock me in the comments.

var query = (from s in db.ForumStatsSet
where s.LogDate >= date1 && s.LogDate <= date2
group s by new {
s.Topic.topicID, s.Topic.subject,
s.Topic.datum, s.Topic.Forum.forumID,
s.Topic.Forum.forumName,
s.Topic.Forum.ForumGroup.name } into g
orderby g.Count() descending
select new TopicStatsData
{
TopicId = g.Key.topicID,
Count = g.Count(),
Subject = g.Key.subject,
ForumId = g.Key.forumID,
ForumName = g.Key.forumName,
ForumGroupName = g.Key.name
});

This code looked fine to me. It’s kind of massive and a lot of joins but it should be used in a admin interface so i did not care that much. But it turned out that it timeout every time in ran it. I had a look at the SQL that was generated and that was not a pretty sight. A massive amount of sub queries and left outer joins.

I posted a question on the new and really really good code community Stackoverflow and got the tip that i should join the tables before group by clue. And that is what i tried to do.

The problem was that i got this error all the time.

from s in db.ForumStatsSet
from t in s.Topic

Error:
An expression of type ‘WhoaAdmin.Models.Topic’ is not allowed in a subsequent from clause in a query expression with source type ‘System.Data.Objects.ObjectQuery’. Type inference failed in the call to ‘SelectMany’.

I tried to google that error and i got nothing. I realised that maybe you have to do the joins in the correct order and that was it and i ended up with this query.

var query = (from fg in db.ForumGroupSet
from f in fg.Forums
from t in f.Topics
from s in t.ForumStats
where s.LogDate >= date1 && s.LogDate <= date2
group s by new { t.topicID,
t.subject,
t.datum,
f.forumID,
f.forumName,
fg.name } into g
orderby g.Count() descending
select new TopicStatsData
{
TopicId = g.Key.topicID,
Count = g.Count(),
Subject = g.Key.subject,
ForumId = g.Key.forumID,
ForumName = g.Key.forumName,
ForumGroupName = g.Key.name
});

The SQL i ended up with looks kind of awful but probably the SQL engine do something like this “under the hood” on regular SQL group by to. At least it is kind of fast. The big diffrence in the generated SQL is that it has replaced all “LEFT OUTER JOINS” with “INNER JOINS” and they are of course faster.

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