Hi I'm trying to do a basic update based on an id using Linq and the entity framework. I'm very new to this but I do not see the problem.
My entity class object is declared at the controller level.
gwwbnEntities db = new gwwbnEntities();
The Method grabs a querystring id and updates the user's registration status who is represented by that id.
public ActionResult ConfirmedAccount(int id)
{
var q = from u in db.user_registration
where u.id == id && u.reg_status == null
select u;
if (q.Any())
{
foreach(var item in q){
user_registration user = item;
user.reg_status = 202;
db.Entry(user).State = EntityState.Modified;
db.SaveChanges();
}
return View();
}
else
{
return RedirectToAction("RegistrationError");
}
}
Any help would be greatly appreciated! Again everything works and populates correctly, but the context object.SaveChanges() method fails everytime.
Thanks guys!
The exception you are seeing is because you have an open data reader (foreach) and you are trying to create transaction (EF does it for you) in SaveChanges(). Call SaveChanges outside the loop.
In addtion: Don't set the state to Modified - EF will detect that properties changed and will automatically set the state accordingly. You may want to do .ToList() on the q before doing anything. At the moment you are sending to queries to the database (one for .Any() and one to get entities). If you do .ToList() you will send only one query that brings entities but .Any() would be called on the list not on the database so it will be much faster and there is no trip to the database. Also ToList() force query evaluation so your foreach loop will not keep the data reader open as it will iterate on the list.
Related
I am using entity framework with repository pattern and unit of work objects..
I have an entity Request with properties "RequestId", "OldRequestId", which can be accessed using requestRepository object.
eg: requestRepostiory.GetAll(), requestRepository.GetFiltered(r=> r.Requestid =10)
If I pass a RequestId, it should retrieve me the specific record.
If the OldRequestId is not null in the retrieved record, it should bring the old request data as well.
It should go on until the OldRequestId is null.
Simple way would be something like this:
public static IEnumerable<Data> GetRecursive(int id)
{
while (true)
{
var tmp = GetFiltered(x => x.Requestid == id);
yield return tmp;
if (tmp.OldRequestId.HasValue)
id = tmp.OldRequestId.Value;
else
yield break;
}
}
Please note, that this code would run make multiple queries towards the database. Performance won't be the best, but it might work for your scenario.
I have the following method inside my asp.net mvc, and i am trying to understand how will entity framework behave when multiple users access the same method :-
public int changeDeviceSwitch(int fromID , int toID)
{
var currentdevices = IT.ITSwitchPorts.Where(a => a.SwitchID == fromID);
int count = 0;
foreach (var d in currentdevices)
{
tms.ITSwitchPorts.Remove(d);
count++;
}
foreach (var d in currentdevices)
{
ITSwitchPort tsp = new ITSwitchPort() { SwitchID = toID, TechnologyID = d.TechnologyID, PortNumber = d.PortNumber };
IT.TMSSwitchPorts.Add(tsp);
}
IT.SaveChanges();
return count;
}
The above method, will mainly, retrieve all the records that have switchID = fromID, then remove all these records and add new records with new switchID.
so my question is what will happen if multiple users access the same method at the same time? as i understand that entity framework can handle the concurrent access in this way as follow:-
-userA call the method
-userB calls the same method
-userA retrieve all the records, delete, then add new records , save.
-userB retrieve all the records , delete, add new records. but when userB reach the saveChnages() ,
entity framework will raise a DbUpdateConcurrencyException when it try to delete a record that no more exists ? so is this what will happen. ?
can anyone advice please?
Thanks
General approach to locking in EF is to use Optimistic locking.
EF Locking docu
SO example
-userB retrieve all the records , delete, add new records. but when userB reach the saveChnages() , entity framework will raise a
DbUpdateConcurrencyException when it try to delete a record that no
more exists ? so is this what will happen. ?
Yes this is what will happen IF you have declared a Concurrency field on the record.
eg
public virtual byte[] RowVersion { get; set; }
I am just starting with linq and entity framework in general and I have a question that may seem naive to all of the advanced users!
I have the following code :
var allDocuments = (from i in companyData.IssuedDocuments select i.IssuedDocumentId).ToList<int>();
var deletedDocuments = allDocuments.Except(updatedDocuments);
and I need to delete all the entities in companyData that their id is stored in deletedDocuments in a disconnected scenario.
Could you please show me a way to do this in an efficient manner?
You could avoid fetching all the ids by specifying you only want deleted ids like this:
var deletedIds = from i in companyData.IssuedDocuments
where !updatedIds.Contains(i.IssuedDocumentId)
select i.IssuedDocumentId
Now if companyData.IssuedDocuments is a DbSet you can tell EF to delete them like this:
foreach (var id in deletedIds)
{
var entity = new MyEntity { Id = id };
companyData.IssuedDocuments.Attach(entity);
companyData.IssuedDocuments.Remove(entity);
}
dbContext.SaveChanges();
This will issue multiple DELETE statements to the database without fetching the full entities into memory.
If companyData.IssuedDocuments is your repository then you could load the full entities instead of just the ids:
var deleted = from i in companyData.IssuedDocuments
where !updatedIds.Contains(i.IssuedDocumentId)
select i
foreach (var entity in deleted)
companyData.IssuedDocuments.Delete(entity);
dbContext.SaveChanges();
Again EF issues multiple DELETE statements to the database
If you can upgrade then EF6 has introduced a RemoveRange method on the DbSet that at you could look at. It may send a single DELETE statement to the database - I haven't tried it yet.
If performance is still an issue then you have to execute sql.
References:
RemoveRange
Deleting an object without retrieving it
How should I remove all elements in a DbSet?
companyData.RemoveAll(x=>deletedDocuments.Contains(x.Id));
I suppose the companyData is a IEnumerable type. The type T contains an Id property, which is the Id of the data. Then deletedDocuments contains the ids of all the documents that we want to remove.
One thing that's important and I should note it here is that the deletion of the documents happens in memory and it doesn't execute it in a db. Otherwise you should provide us with the version of entity framework you use and how you access you implelemnt your CRUD operations against your db.
Firstly I would like to thank you all for your suggestions.
I followed Christos Paisios suggestion but I was getting all kinds of exceptions when I was trying to persist the changes to the DB and the way that I finally managed to solve the issues was by adding the following override in my DbContext class
public override int SaveChanges()
{
var orphanedResponses = ChangeTracker.Entries().Where(
e => (e.State == EntityState.Modified || e.State == EntityState.Added) &&
e.Entity is IssuedDocument &&
e.Reference("CompanyData").CurrentValue == null);
foreach (var orphanedResponse in orphanedResponses)
{
IssuedDocuments.Remove(orphanedResponse.Entity as IssuedDocument);
}
return base.SaveChanges();
}
I have a table of data with a list of key value pairs in it.
Key Value
--------------------
ElementName PrimaryEmail
Email someemail#gmail.ca
Value Content/Images/logo-here.jpg
I am able to generate new items on my client webpage. When, I create a new row on the client and save it to the server by executing the following code the item saves to the database as expected.
public ViewResult Add(CardElement cardElement)
{
db.Entry(obj).State = EntityState.Added;
db.SaveChange();
return Json(obj);
}
Now, when I want to delete my objects by sending another ajax request I get a failure.
public void Delete(CardElement[] cardElements)
{
foreach (var cardElement in cardElements)
{
db.Entry(cardElement).State = EntityState.Deleted;
}
db.SaveChanges();
}
This results in the following error.
Store update, insert, or delete statement affected an unexpected number of rows (0). Entities may have been modified or deleted since entities were loaded. Refresh ObjectStateManager entries.
I have tried other ways of deleting including find by id remove and attach and delete but obviously I am approaching in the right fashion.
I am not sure what is causing your issue, but I tend to structure my deletes as follows:
public void Delete(CardElement[] cardElements)
{
foreach (var cardElement in cardElements)
{
var element = db.Table.Where(x => x.ID == cardElement.ID).FirstOrDefault();
if(element != null)
db.DeleteObject(element);
}
db.SaveChanges();
}
although I tend to do database first development, which may change things slightly.
EDIT: the error you are receiving states that no rows were updated. When you pass an object to a view, then pass it back to the controller, this tends to break the link between the object and the data store. That is why I prefer to look up the object first based on its ID, so that I have an object that is still linked to the data store.
I am working with code first approach in EDM and facing an error for which I can't the solution.Pls help me
LINQ to Entities does not recognize the method 'Boolean
CheckMeetingSettings(Int64, Int64)' method, and this method cannot be
translated into a store expression.
My code is following(this is the query which I have written
from per in obj.tempPersonConferenceDbSet
where per.Conference.Id == 2
select new PersonDetials
{
Id = per.Person.Id,
JobTitle = per.Person.JobTitle,
CanSendMeetingRequest = CheckMeetingSettings(6327,per.Person.Id)
}
public bool CheckMeetingSettings(int,int)
{
///code I have written.
}
Please help me out of this.
EF can not convert custom code to SQL. Try iterating the result set and assigning the property outside the LINQ query.
var people = (from per in obj.tempPersonConferenceDbSet
where per.Conference.Id == 2
order by /**/
select new PersonDetials
{
Id = per.Person.Id,
JobTitle = per.Person.JobTitle,
}).Skip(/*records count to skip*/)
.Take(/*records count to retrieve*/)
.ToList();
people.ForEach(p => p.CanSendMeetingRequest = CheckMeetingSettings(6327, p.Id));
With Entity Framework, you cannot mix code that runs on the database server with code that runs inside the application. The only way you could write a query like this, is if you defined a function inside SQL Server to implement the code that you've written.
More information on how to expose that function to LINQ to Entities can be found here.
Alternatively, you would have to call CheckMeetingSettings outside the initial query, as Eranga demonstrated.
Try:
var personDetails = obj.tempPersonConferenceDbSet.Where(p=>p.ConferenceId == 2).AsEnumerable().Select(p=> new PersonDetials
{
Id = per.Person.Id,
JobTitle = per.Person.JobTitle,
CanSendMeetingRequest = CheckMeetingSettings(6327,per.Person.Id)
});
public bool CheckMeetingSettings(int,int)
{
///code I have written.
}
You must use AsEnumerable() so you can preform CheckMeetingSettings.
Linq to Entities can't translate your custom code into a SQL query.
You might consider first selecting only the database columns, then add a .ToList() to force the query to resolve. After you have those results you van do another select where you add the information from your CheckMeetingSettings method.
I'm more comfortable with the fluid syntax so I've used that in the following example.
var query = obj.tempPersonConferenceDbSet
.Where(per => per.Conference.Id == 2).Select(per => new { Id = per.Person.Id, JobTitle = per.Person.JobTitle })
.ToList()
.Select(per => new PersonDetails { Id = per.Id,
JobTitle = per.JobTitle,
CanSendMeetingRequest = CheckMeetingSettings(6327, per.Person.Id) })
If your CheckMeetingSettings method also accesses the database you might want to consider not using a seperate method to prevent a SELECT N+1 scenario and try to express the logic as part of the query in terms that the database can understand.