Saving and updating (SQL Server rows) using SubSonic 3.0 and LINQ - sql-server

I feel foolish asking such a fundamental question but it would be more foolish not to ask :)
I have been using SubSonic 2.x for years and love it (Thanks Rob and co.).
I have started a pilot project using SubSonic 3.0.0.4 and have chosen the LINQ T4 Templates (excuse me if I have the terminology wrong).
Now I am new to LINQ but I am doing OK working out how to build the queries.
What I am REALLY struggling with is how to create and update data with the new toolkit.
Previously it was super simple where I could:
'new' an object if I didn't have one
or Fetch or construct an existing one by id
set some properties
then 'Save()' it
Fantastic and saved me hours.
Now in the new toolkit some things seem to be the same like:
creating an object
setting some properties
but right now some things seem a lot harder like:
Loading an object seems to be:
db.Product.FirstOrDefault(x => ProductID.Id == 123);
Inserting seems to be:
db.Insert.Into<Northwind.Region>(
x => x.RegionID,
x => x.RegionDescription)
.Values(6, "Hawaii").Execute();
Updating an object seems even harder:
db.Update<Product>()
.Set(x => x.UnitPrice == 100, x => x.ProductName == "Test")
.Where(x => x.ProductID == 1).Execute();
The documentation (http://subsonicproject.com/docs/Linq_Updates) talks about using the Repository but that just doesn't exist/get generated with the T4 templates I am using.
So any help to let me know that:
I have obviously set this up wrong
I have no idea what I am doing and the way to do it is ... insert answer here
I understand it correctly and should just suck it up
would be greatly appreciated.
If any more info is needed please let me know.
Thanks in advance.
Mark
---- Update ----
To summarise the answer from Denis:
LINQ is a query language not an ORM
You can get to the Repository object via:
var repo = new SubSonic.Repository.SubSonicRepository(db);

Hmm.. I migrated one of my projects to the SubSonic 3 too but frankly have not had any troubles saving the entities. I use the same ActiveRecord techniques and it still works great for me. For example, to retrieve an entity I am issuing:
var product = new Product(p => p.Id == 123);
For inserting:
var product = new Product();
product.RegionID = 6;
product.RegionDescription = "Hawaii";
product.Save();
Updating:
product.UnitPrice = 100;
product.ProductName = "Test";
product.Save();
As you can see you can still use the same Save() method.
So, not really sure why you try to do that through the 'db' context even though it can be used too :) Am I missing something?

Related

XPcollection not loaded - why?

This must be something very simple, I just don't see it (and can not find the answer :(
I am trying to learn DevExpress controls and have read that eXpress Persistent Objects is recommended for O/R mapping.
1) I have an existing SQL Server Compact 4.0 database for which I generated ORM
2) I have a Winform with XtraGrid.GridControl gridControl1
3) In Form_Load event I have this code:
XPCollection cName = new XPCollection(typeof(WindowsFormsApplication1.DUzskv1r6.XPO_TableName));
int c = cName.Count; //didn't help...
cName.DisplayableProperties = "Name;Nr"; //choose columns to display
gridControl1.MainView.PopulateColumns();
gridControl1.DataSource = cName;
I have read that it using "delayed loading" - loading when it is necessary (http://documentation.devexpress.com/#XPO/clsDevExpressXpoXPCollectiontopic), but reading XPcollections record Count didn't do the trick as it was suggested.
As a result I get an empty gridControl1 with columns "Name" and "Nr".
Please help - what am I missing?
I think the issue is somewhere in your datalayer initialization.
You use XPCollection with default session, maybe you forgot to initialize it.
The best way is to specify the session is in the XPCollection contractor.

Grails/GORM domain saving - transient object workaround

I found a work around to a problem I had, and I want to know if it is valid or not. It is a similar problem to: Grails Gorm : Object references an unsaved transient instance
Lets assume I have two domain Objects (names changed to protect the guilty).
public class Shelf {
String name
Set<Book> books = [] as Set
static hasMany = [books: Book]
}
and
public class Book {
String title
Shelf shelf
}
So this means that 1 Shelf contains 0 to many Books, and one Book can be on only one Shelf.
This Shelf is very large. And at some point, it contains 80,000 Books. All stored nicely in the DB. Of course, adding new Books is getting slower and slower.
This is done by:
Book book1 = new Book("Awesome Title")
existingShelf.addToBooks(book1)
existingShelf.save(flush: true) // super slow
This is slow. Mainly (I assume) because GORM has to confirm the other 80,000 records.
So I did this to try to work around the slow point.
Book book2 = new Book("Awesome Title 2")
book2.save(flush: true)
This gives me an "Object references an unsaved transient instance", which I guess makes sense - the "shelf" value is empty.
So I did something a little weird:
Book book3 = new Book("Awesome Title 3")
book3.shelf = new Shelf()
book3.shelf.id = <known/valid id here>
book2.save(flush: true)
This works. It saves. There are no referential errors. Further code that depends on this... works.
I just made a call that last minutes and reduced it down to seconds.
But that seems too easy. I'm sure I worked around Grails magic some how. And probably broke something in the process.
Advice? Explanations?
Yes, using addTo* methods can be slow. If you look at the generated SQL you'll understand why. Doing the following:
new Book(title: "GORM Performance", shelf: grailsShelf).save()
will be faster and there is technically nothing wrong with it. Just be aware of that your instance of grailsShelf.books will not contain the new book until you've refreshed the collection from the database. This is part of what the addTo* method does for you.
Side note:
Set<Book> books = [] as Set
is unnecessary.

Select query of sqlite in metro app?

I have seen quite a number of examples describing the usage of SQLite in Metro app. Most of the examples have either Orderby/Insert/Delete statements. May I know how do I get the data from a pre-populated db using the Select statement?
Secondly, how does someone store the data into an array or arrayList after the execution of the query?
Kindly help me with this,
Thanks.
See if this example is what you're looking for:
return db.runAsync('SELECT * FROM Table');
Here is a pretty useful article on it.
Extending the example to C#:
SQLiteAsyncConnection conn = new SQLiteAsyncConnection("people");
var query = conn.Table<Person>().Select();
var result = await query.ToListAsync();

How do I SubmitChanges on multiple tables that are related in LinqToSql?

I'm making a Windows Phone 7.1 application, and I'm having a lot of trouble submitting changes to my database. Here is the structure of the tables in my database:
Day <-1-----*-> TrainingSession <-many-----1-> Sport
So, a single day can have many training sessions, and a training session has one sport. A single sport can naturally be in many different training sessions.
The primary keys look like this:
Day - DateTime
TrainingSession - int (DB generated)
Sport - nvarchar(200)
Sports will simply have attributes sportName, and an iconFileName.
I've set up Associations by putting EntitySet in both Day and Sport, and TrainingSession has EntityRef and EntityRef. I'm not 100% sure if Sport needs the EntitySet, so please correct me if I'm wrong. For the moment, I just hard-coded some sports in my Sport class for testing, and you'll see me retrieving an ObservableCollection to get those out.
Here is how I am trying to create a collection of days with training sessions, each training session having different sports:
public void CreateDay(DateTime date)
{
FitPlanDataContext calendarDatabase = new FitPlanDataContext(FitPlanDataContext.ConnectionString);
DateTime firstDate = new DateTime(date.Year, date.Month, 1);
DayItem dayItem = new DayItem();
dayItem.DateTime = firstDate;
fillTestDayItemWithRandomData(dayItem);
calendarDatabase.DayItems.InsertOnSubmit(dayItem);
calendarDatabase.SubmitChanges();
}
private void fillTestDayItemWithRandomData(DayItem dayItem)
{
ObservableCollection<SportArt> sportArtCollection = SportArtController.GetAllSports();
dayItem.TrainingSessions = new EntitySet<TrainingSession>();
ObservableCollection<TrainingSession> trainingSessionCollection = new ObservableCollection<TrainingSession>();
TrainingSession trainingSession1 = new TrainingSession();
trainingSession1.DayItem = dayItem;
trainingSession1.SportArt = sportArtCollection[1];
trainingSessionCollection.Add(trainingSession1);
TrainingSession trainingSession2 = new TrainingSession();
trainingSession2.DayItem = dayItem;
trainingSession2.SportArt = sportArtCollection[2];
trainingSessionCollection.Add(trainingSession2);
FitPlanDataContext calendarDatabase = new FitPlanDataContext(FitPlanDataContext.ConnectionString);
calendarDatabase.TrainingSessions.InsertAllOnSubmit<TrainingSession>(trainingSessionCollection);
}
This code is not working for me, and it is giving me the following error:
NotSupportedException was Unhandled:
An attempt has been made to Attach or Add an entity that is not new, perhaps having been loaded from another DataContext. This is not supported.
Before I got this error, I was also getting NullReferenceExceptions.
I've been looking around for a solution, and I saw some people used Detach or workarounds with Attach, but I havent figured out how I could implement it to my code. Could anyone give me a helping hand with this?
Also, I thought the NullReferenceException could be coming from the fact that I'm not saving any sports to the database, could this be so?
So I messed around with it a lot, and today I finally found the solution I was looking for.
It seems I asked the question wrong. I didn't include the query from the database, which is probably important to add. I actually omitted a lot of the code to keep things simple in my question, but looks like I omitted too much.
Anyways, it turned out the way I setup the database structure was correct, and nothing had to be changed there.
So here's what I did to get it working:
-The call to the method that fills the day with training sessions needed to go after submitting changes about the day. This is because days have training sessions, and I cant save training sessions without the day already in the database.
-I added using statements around the places where I need to use the datacontext instead of just creating an instance of the datacontext with a local variable. This ensures that the datacontext lives only in the scope of the using statment.
(I changed the DateTime of the day to be the date given as the parameter to the method)
public void CreateDay(DateTime date)
{
DayItem dayItem = new DayItem();
dayItem.DateTime = date;
using (FitPlanDataContext calendarDatabase = new FitPlanDataContext(FitPlanDataContext.ConnectionString))
{
calendarDatabase.DayItems.InsertOnSubmit(dayItem);
calendarDatabase.SubmitChanges();
}
fillTestDayItemWithRandomData(dayItem);
}
Then, the changes to the method that fills the day with training sessions go like this:
-I open a using statement where I instantiate a new datacontext. Then I access the database to retrieve a list of all the sports, and also the day that I need to update. I find the day I need to update by dayItemParameter. (Remember that retrieving from the database will give you a collection.)
-I create my new training sessions and fill their properties. Note that the day I retrieved from the database is the value of a training session's property because the training session is a child of day, and needs to know who its parent day is.
-I removed the instantiation of EntitySet because I realized that I already instantiate it in the constructor of the DayItem class.
-Lastly, I add all the new training sessions into a collection, and save them all to the database at once using InsertAllOnSubmit(collection).
private void fillTestDayItemWithRandomData(DayItem dayItemParameter)
{
using (FitPlanDataContext calendarDatabase = new FitPlanDataContext(FitPlanDataContext.ConnectionString))
{
ObservableCollection<SportArt> sportArtCollection;
var sportArts = (from SportArt sportArt in calendarDatabase.SportArts
select sportArt);
sportArtCollection = new ObservableCollection<SportArt>(sportArts);
ObservableCollection<DayItem> dayItemCollection;
var dayItems = (from DayItem dayItem in calendarDatabase.DayItems
where dayItem.DateTime == dayItemParameter.DateTime
select dayItem);
dayItemCollection = new ObservableCollection<DayItem>(dayItems);
DayItem foundDayItem = dayItemCollection[0];
ObservableCollection<TrainingSession> trainingSessionCollection = new ObservableCollection<TrainingSession>();
TrainingSession trainingSession1 = new TrainingSession();
trainingSession1.DayItem = foundDayItem;
trainingSession1.SportArt = sportArtCollection[1];
trainingSessionCollection.Add(trainingSession1);
TrainingSession trainingSession2 = new TrainingSession();
trainingSession2.DayItem = foundDayItem;
trainingSession2.SportArt = sportArtCollection[2];
trainingSessionCollection.Add(trainingSession2);
calendarDatabase.TrainingSessions.InsertAllOnSubmit<TrainingSession>(trainingSessionCollection);
calendarDatabase.SubmitChanges();
}
}
Conclusion:
The main problem I was having was that I was trying to save training sessions to a day that wasn't submitted to the database. The next big problem (that I think many others have) is that reading and updating of an entity has to be in the same datacontext. So, you can't create a datacontext to retrieve a day, then use another datacontext to add a training session to that day (even if you saved the value of the day to a local variable). You need to retrieve the day and save training sessions to it all in the same data context.
At the moment, my application is working, but it is quite sluggish. In this question, I'm asking about just one day, but in my actual program, I'm creating hundreds of days, which means a lot of opening and closing of the database. If anyone has suggestions to how I can
optimize the process, I'm open ears.
I realize and apologize that this post got so long, but writing it helped me to understand the situation with more depth, and I really hope that it'll help others too.

Cannot retrieve user object from foreign key relationships using Linq to Entities statement

I'm trying to retrieve a user object from a foreign key reference but each time I try to do so nothing gets returned...
My table is set up like this:
FBUserID long,
UserID uniqueidentifier
so I have my repository try to get the User when it's provided the FBUserID:
public User getUserByFBuid(long uid)
{
User fbUser = null;
IEnumerable<FBuid> fbUids = _myEntitiesDB.FBuidSet.Where(user => user.FBUserID == uid);
fbUser = fbUids.FirstOrDefault().aspnet_Users;
return fbUser;
}
I've checked that the uid (FBUserID) passed in is correct, I've check that the UserID is matched up to the FBUserID. And I've also checked to make sure that fbUids.Count() > 0...
I've returned fbUids.FirstOrDefault().FBUserID and gotten the correct FBUserID, but any time I try to return the aspnet_Users or aspnet_Users.UserName, etc... I don't get anything returned. (I'm guessing it's getting an error for some reason)
I don't have debugging set up properly so that's probably why i'm having so much troubles... but so far all the checking I've done I've been doing return this.Json(/* stuff returned form the repository */) so that I can do an alert when it gets back to the javascript.
Anyone know why I would have troubles retrieving the user object from a foreign key relationship like that?
Or do you have any suggestions as to finding out what's wrong?
For now, with Entity Framework 1, you don't get automatic delayed loading, e.g. if you want to traverse from one entity to the next, you need to either do an .Include("OtherEntity") on your select to include those entities in the query, or you need to explicitly call .Load("OtherEntity") on your EntityContext to load that entity.
This was a design decision by the EF team not to support automagic deferred loading, since they considered it to be too dangerous; they wanted to make it clear and obvious to the user that he is also including / loading a second set of entities.
Due to high popular demand, the upcoming EF v4 (to be released with .NET 4.0 sometime towards the end of 2009) will support the automatic delayed loading - if you wish to use it. You need to explicitly enable it since it's off by default:
context.ContextOptions.DeferredLoadingEnabled = true;
See some articles on that new feature:
A Look at Lazy Loading in EF4
POCO Lazy Loading
Don't know if this is what you are asking but i do a join like so;
var votes = from av in dc.ArticleVotes
join v in dc.Votes on av.voteId equals v.id
where av.articleId == articleId
select v;
Did this help or am I off base?

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