I'm using vb.net and entity framework.
I add a new object (Myobject) and before the savechanges is called , I try to modify it.
After that I check the context.entry(Myobject).state and the result is EntityState.Modified.
But this is a new record . Why the state isn't Entitystate.Added ?
Thank you !
From the documentation
Added: The object is new, has been added to the object context, and the SaveChanges method has not been called. After the changes are saved, the object state changes to Unchanged. Objects in the Added state do not have original values in the ObjectStateEntry.
You can use the EntityState.Added like this
using (var context = new BloggingContext())
{
var blog = new Blog { Name = "ADO.NET Blog" };
context.Entry(blog).State = EntityState.Added;
context.SaveChanges();
}
Related
I am creating an instance of Unit of Work manually and use it to create new row. The problem is that even though my row is created successfully, the EntityId property in SaveResponse is null. (Error property is also null)
using (var conn = sqlConnStrings.NewByKey("Default"))
{
using (var uow = new UnitOfWork(conn))
{
resp = Create(uow, req);
// resp.EntityId is null despite successful insert to DB.
uow.Commit();
}
// accessing resp variable outside the using block doesn't help.
}
i have a database containing Song objects. The song class has > 30 properties.
My Music Tagging application is doing changes on a song on the file system.
It then does a lookup in the database using the filename.
Now i have a Song object, which i created in my Tagging application by reading the physical file and i have a Song object, which i have just retrieved from the database and which i want to update.
I thought i just could grab the ID from the database object, replace the database object with my local song object, set the saved id and store it.
But Raven claims that i am replacing the object with a different object.
Do i really need to copy every single property over, like this?
dbSong.Artist = songfromFilesystem.Artist;
dbSong.Album = songfromFileSystem.Album;
Or are there other possibilities.
thanks,
Helmut
Edit:
I was a bit too positive. The suggestion below works only in a test program.
When doing it in my original code i get following exception:
Attempted to associate a different object with id 'TrackDatas/3452'
This is produced by following code:
try
{
originalFileName = Util.EscapeDatabaseQuery(originalFileName);
// Lookup the track in the database
var dbTracks = _session.Advanced.DocumentQuery<TrackData, DefaultSearchIndex>().WhereEquals("Query", originalFileName).ToList();
if (dbTracks.Count > 0)
{
track.Id = dbTracks[0].Id;
_session.Store(track);
_session.SaveChanges();
}
}
catch (Exception ex)
{
log.Error("UpdateTrack: Error updating track in database {0}: {1}", ex.Message, ex.InnerException);
}
I am first looking up a song in the database and get a TrackData object in dbTracks.
The track object is also of type TrackData and i just put the ID from the object just retrieved and try to store it, which gives the above error.
I would think that the above message tells me that the objects are of different types, which they aren't.
The same error happens, if i use AutoMapper.
any idea?
You can do what you're trying: replace an existing object using just the ID. If it's not working, you might be doing something else wrong. (In which case, please show us your code.)
When it comes to updating existing objects in Raven, there are a few options:
Option 1: Just save the object using the same ID as an existing object:
var song = ... // load it from the file system or whatever
song.Id = "Songs/5"; // Set it to an existing song ID
DbSession.Store(song); // Overwrites the existing song
Option 2: Manually update the properties of the existing object.
var song = ...;
var existingSong = DbSession.Load<Song>("Songs/5");
existingSong.Artist = song.Artist;
existingSong.Album = song.Album;
Option 3: Dynamically update the existing object:
var song = ...;
var existingSong = DbSession.Load<Song>("Songs/5");
existingSong.CopyFrom(song);
Where you've got some code like this:
// Inside Song.cs
public virtual void CopyFrom(Song other)
{
var props = typeof(Song)
.GetProperties(System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.Instance)
.Where(p => p.CanWrite);
foreach (var prop in props)
{
var source = prop.GetValue(other);
prop.SetValue(this, source);
}
}
If you find yourself having to do this often, use a library like AutoMapper.
Automapper can automatically copy one object to another with a single line of code.
Now that you've posted some code, I see 2 things:
First, is there a reason you're using the Advanced.DocumentQuery syntax?
// This is advanced query syntax. Is there a reason you're using it?
var dbTracks = _session.Advanced.DocumentQuery<TrackData, DefaultSearchIndex>().WhereEquals("Query", originalFileName).ToList();
Here's how I'd write your code using standard LINQ syntax:
var escapedFileName = Util.EscapeDatabaseQuery(originalFileName);
// Find the ID of the existing track in the database.
var existingTrackId = _session.Query<TrackData, DefaultSearchIndex>()
.Where(t => t.Query == escapedFileName)
.Select(t => t.Id);
if (existingTrackId != null)
{
track.Id = existingTrackId;
_session.Store(track);
_session.SaveChanges();
}
Finally, #2: what is track? Was it loaded via session.Load or session.Query? If so, that's not going to work, and it's causing your problem. If track is loaded from the database, you'll need to create a new object and save that:
var escapedFileName = Util.EscapeDatabaseQuery(originalFileName);
// Find the ID of the existing track in the database.
var existingTrackId = _session.Query<TrackData, DefaultSearchIndex>()
.Where(t => t.Query == escapedFileName)
.Select(t => t.Id);
if (existingTrackId != null)
{
var newTrack = new Track(...);
newTrack.Id = existingTrackId;
_session.Store(newTrack);
_session.SaveChanges();
}
This means you already have a different object in the session with the same id. The fix for me was to use a new session.
I am trying to pass an object from one controller to another controller, but it is not behaving in the way that I would like it to. In the following ApplicantMainController, I am instantiating an object called ApplicationQuestions (which contains a List<ApplicationQuestion> object as one of its members) and then attempting to pass it via the RedirectToAction method call:
public ActionResult FormAction(FormCollection collection)
{
if (collection["cmdSearch"] != null)
{
// more code above...
ApplicationQuestions questions = new ApplicationQuestions();
MultipleChoiceQuestion q1 = new MultipleChoiceQuestion("Can you lift 50 pounds?");
MultipleChoiceQuestion q2 = new MultipleChoiceQuestion("Are you at least 18 years of age?");
MultipleChoiceQuestion q3 = new MultipleChoiceQuestion("Are you legally able to work in the US?");
MultipleChoiceQuestion q4 = new MultipleChoiceQuestion("Have you ever been convicted of a felony?");
q1.AddPossibleAnswer(1, new Answer("Yes", true));
q1.AddPossibleAnswer(2, new Answer("No", false));
q2.AddPossibleAnswer(1, new Answer("Yes", true));
q2.AddPossibleAnswer(2, new Answer("No", false));
q3.AddPossibleAnswer(1, new Answer("Yes", true));
q3.AddPossibleAnswer(2, new Answer("No", false));
q4.AddPossibleAnswer(1, new Answer("Yes", false));
q4.AddPossibleAnswer(2, new Answer("No", true));
questions.AddQuestion(q1);
questions.AddQuestion(q2);
questions.AddQuestion(q3);
questions.AddQuestion(q4);
// not sure how to pass the object here??
return RedirectToAction("Apply", "ApplicantApply", new { model = questions });
}
}
When I redirect to the controller, it appears to make it:
private ApplicationQuestions m_questions;
// more code ...
public ActionResult Apply(ApplicationQuestions questions)
{
m_questions = questions;
return RedirectToAction("NextQuestion", "ApplicantApply");
}
However, though the reference is now bound to the parameter passed to the Apply method, the debugger tells me that the reference to the collection questions does not contain any elements, though clearly the caller passed a collection with four elements. I think I am misunderstanding how this works -- what is the proper way to communicate objects between controllers like this?
One option is to use TempData to hold the object during the redirect.
TempData["MyCoolData"] = questions;
return RedirectToAction("Apply", "ApplicantApply");
Then grab the object out of TempData in the other action:
m_questions = (ApplicationQuestions)TempData["MyCoolData"];
See this question and its answers for more information.
I have the following data model:
I am writing a WCF service that needs to support adding new Report:
public bool CreateNewReport(Report report)
{
MyEntities context = new MyEntities();
context.AddToReports(Report);
context.SaveChanges();
}
So my method gets a report object that was made on the client and adds it to the database throught the data context. (all of the members are included in the DataContract)
My question is regarding navigation properties.
Do the client also needs to create a user object and put it in the new report object before sending it ?
What is the best way to approach this ? one way i think of is adding a UserId field in the ReportEntity
when a new report is inserted, how do i update the UserEntity Report nav property that with the new Report ?
Thanks.
If you import your database, generate navigation properties (the properties in your picture) AND foreign id properties (then you have for example an User and UserID property in your report class). This way you can set the UserID in your client and send it to the server and add it with AddToReports... If you send the whole user object you have to attach it to the entity context otherwise the user will be created once again...
Attach the referenced user: (but it's better to send the user only by id)
public bool CreateNewReport(Report report)
{
using (MyEntities context = new MyEntities())
{
context.AddToReports(Report);
context.Users.Attach(report.User);
context.SaveChanges();
}
}
To change the report of a user:
public bool ChangeUserToNewReport(int userid, Report newReport)
{
using (MyEntities context = new MyEntities())
{
var user = context.Users.Single(u => u.ID = userid);
user.Report = newReport;
context.SaveChanges();
}
}
For an existing report:
public bool ChangeUserReport(int userid, Report existingReport)
{
using (MyEntities context = new MyEntities())
{
context.Reports.Attach(existingReport);
var user = context.Users.Single(u => u.ID = userid);
user.Report = existingReport;
context.SaveChanges();
}
}
This is a sample how your model should look like. Double click on the association line to open the dialog. You can see that the Person and PersonID properties are the same. If you create your model like this, VS should generate the correct SQL.
In the dbml designer I've set Update Check to Never on all properties. But i still get an exception when doing Attach: "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." This approach seems to have worked for others on here, but there must be something I've missed.
using(TheDataContext dc = new TheDataContext())
{
test = dc.Members.FirstOrDefault(m => m.fltId == 1);
}
test.Name = "test2";
using(TheDataContext dc = new TheDataContext())
{
dc.Members.Attach(test, true);
dc.SubmitChanges();
}
The error message says exactly what is going wrong: You are trying to attach an object that has been loaded from another DataContext, in your case from another instance of the DataContext. Dont dispose your DataContext (at the end of the using statement it gets disposed) before you change values and submit the changes. This should work (all in one using statement). I just saw you want to attach the object again to the members collection, but it is already in there. No need to do that, this should work just as well:
using(TheDataContext dc = new TheDataContext())
{
var test = dc.Members.FirstOrDefault(m => m.fltId == 1);
test.Name = "test2";
dc.SubmitChanges();
}
Just change the value and submit the changes.
Latest Update:
(Removed all previous 3 updates)
My previous solution (removed it again from this post), found here is dangerous. I just read this on a MSDN article:
"Only call the Attach methods on new
or deserialized entities. The only way
for an entity to be detached from its
original data context is for it to be
serialized. If you try to attach an
undetached entity to a new data
context, and that entity still has
deferred loaders from its previous
data context, LINQ to SQL will thrown
an exception. An entity with deferred
loaders from two different data
contexts could cause unwanted results
when you perform insert, update, and
delete operations on that entity. For
more information about deferred
loaders, see Deferred versus Immediate
Loading (LINQ to SQL)."
Use this instead:
// Get the object the first time by some id
using(TheDataContext dc = new TheDataContext())
{
test = dc.Members.FirstOrDefault(m => m.fltId == 1);
}
// Somewhere else in the program
test.Name = "test2";
// Again somewhere else
using(TheDataContext dc = new TheDataContext())
{
// Get the db row with the id of the 'test' object
Member modifiedMember = new Member()
{
Id = test.Id,
Name = test.Name,
Field2 = test.Field2,
Field3 = test.Field3,
Field4 = test.Field4
};
dc.Members.Attach(modifiedMember, true);
dc.SubmitChanges();
}
After having copied the object, all references are detached, and all event handlers (deferred loading from db) are not connected to the new object. Just the value fields are copied to the new object, that can now be savely attached to the members table. Additionally you do not have to query the db for a second time with this solution.
It is possible to attach entities from another datacontext.
The only thing that needs to be added to code in the first post is this:
dc.DeferredLoadingEnabled = false
But this is a drawback since deferred loading is very useful. I read somewhere on this page that another solution would be to set the Update Check on all properties to Never. This text says the same: http://complexitykills.blogspot.com/2008/03/disconnected-linq-to-sql-tips-part-1.html
But I can't get it to work even after setting the Update Check to Never.
This is a function in my Repository class which I use to update entities
protected void Attach(TEntity entity)
{
try
{
_dataContext.GetTable<TEntity>().Attach(entity);
_dataContext.Refresh(RefreshMode.KeepCurrentValues, entity);
}
catch (DuplicateKeyException ex) //Data context knows about this entity so just update values
{
_dataContext.Refresh(RefreshMode.KeepCurrentValues, entity);
}
}
Where TEntity is your DB Class and depending on you setup you might just want to do
_dataContext.Attach(entity);