I am develloping a web form that has a wizard with 4 steps:
On each step I'me creating new entities generated from a database.
The problem is that being a wizzard, the user can change the properties of the controls that will originate the values to be stored.
So I need to release the created entity objects or return that entity values to the original rows stored on the database.
How can I do this.
Should'n it work if I set each created entity object to null?
By the way this is how I'm doing it:
entities = new Entities();
...
Client client = new Client();
client.name = tbxName.text
...
entities.SaveChanges();
entities.Connection.Close();
So If this code is executed on the 2nd wizard part of a wizard of 3 parts and I go back and fowrward through this set more the once the client creating runs more than once, so there's my problem.
So how can I unCreate it :-P
Thannks!!!
If you are building wizard you must manage it as single operation. It means that you have to store built entity graph in the session and save it only if whole wizard is completed and confirmed. Your step logic also must check if related data are already present in the entity graph and use them instead of creating new one.
If your using Entity Framework, why not implement the Unit Of Work pattern? Each part of your wizard builds the UoW and the "final step" commits the unit of work.
There was an article called "The Unit Of Work Pattern And Persistence Ignorance" in MSDN magazine a few years ago that explains the concept.
This is the way I do it:
1- Create a place where you can manage your Session variables :
public class SessionObjects { }
2- I save my ObjectContext in the Session so I create a property to manage it in the mentioned class :
public static ObjectContextEntities ObjectContextEntities
{
get
{
return (ObjectContextEntities)HttpContext.Current.Session["ObjectContextEntities"];
}
set
{
HttpContext.Current.Session["ObjectContextEntities"] = value;
}
}
3- Initialize the ObjectContext on the wizard's start and dispose it on its end:
void StartWizard()
{
SessionObject.ObjectContextEntities = new ObjectContextEntities();
}
void StartWizard()
{
SessionObject.ObjectContextEntities = new ObjectContextEntities();
}
void EndWizard()
{
((ObjectContextEntities)SessionObject.ObjectContextEntities).Dispose();
}
4- To save wizard result to the database you can call:
void SaveWizard()
{
((ObjectContextEntities)SessionObject.ObjectContextEntities).SaveAllChanges();
}
5- To reset wizard simply call EndWizard then StartWizard .
I guess you know how to manage your ObjectEntity objects and in the ObjectContext so you can continue from here by your self ..
Related
To make updates to a record of SQL Server using Entity Framework Core, I query the record I need to update, make changes to the object and then call .SaveChanges(). This works nice and clean.
For example:
var emp = _context.Employee.FirstOrDefault(item => item.IdEmployee == Data.IdEmployee);
emp.IdPosition = Data.IdPosition;
await _context.SaveChangesAsync();
But is there a standard method if I want to update multiple records?
My first approach was using a list passing it to the controller, but then I would need to go through that list and save changes every time, never really finished this option as I regarded it as not optimal.
For now what I do is instead of passing a list to the controller, I pass each object to the controller using a for. (kind of the same...)
for(int i = 0; i < ObjectList.Count; i ++)
{
/* Some code */
var httpResponseObject = await MyRepositories.Post<Object>(url+"/Controller", Object);
}
And then do the same thing on the controller as before, when updating only one record, for each of the records...
I don't feel this is the best possible approach, but I haven't found another way, yet.
What would be the optimal way of doing this?
Your question has nothing to do with Blazor... However, I'm not sure I understand what is the issue. When you call the SaveChangesAsync method, all changes in your context are committed to the database. You don't have to pass one object at a time...You can pass a list of objects
Hope this helps...
Updating records in bulk using Entity Framework or other Object Relational Mapping (ORM) libraries is a common challenge because they will run an UPDATE command for every record. You could try using Entity Framework Plus, which is an extension to do bulk updates.
If updating multiple records with a single call is critical for you, I would recommend just writing a stored procedure and call if from your service. Entity Framework can also run direct queries and stored procedures.
It looks like the user makes some changes and then a save action needs to persist multiple records at the same time. You could trigger multiple AJAX calls—or, if you need, just one.
What I would do is create an endpoint—with an API controller and an action—that's specific to your needs. For example, to update the position of records in a table:
Controller:
/DataOrder
Action:
[HttpPut]
public async void Update([FromBody] DataChanges changes)
{
foreach(var change in changes)
{
var dbRecord = _context.Employees.Find(change.RecordId);
dbRecord.IdPosition = change.Position;
}
_context.SaveChanges();
}
public class DataChanges
{
public List<DataChange> Items {get;set;}
public DataChangesWrapper()
{
Items = new List<DataChange>();
}
}
public class DataChange
{
public int RecordId {get;set;}
public int Position {get;set;}
}
The foreach statement will execute an UPDATE for every record. If you want a single database call, however, you can write a SQL query or have a stored procedure in the database and pass the data as a DataTable parameter instead.
I am working an Symfony 2.8 based web app project which currently uses Doctrine 2. The project is basically a simple ToDo list application which can be synced with a mobile app (iOS/Android).
While reading the Update notes of Doctrine 3 I discovered, that EntityManager::merge will no longer be supported.
An alternative to EntityManager#merge() is not provided by ORM 3.0,
since the merging semantics should be part of the business domain
rather than the persistence domain of an application. If your
application relies heavily on CRUD-alike interactions and/or PATCH
restful operations, you should look at alternatives such as
JMSSerializer.
I am not sure what is the best/correct way to replace EntityManager::merge?
Where do I use merge:
During the sync of the mobile apps with the web app the data is transferred as serialized JSON which is than de-serialized by JMSSerializer to an entity object. When the web app receives a ToDoEntry object this way, it can be a new ToDo-Entry (not known in the web app yet) or an updated existing entry. Either way, the received object is not managed by the EntityManager. Thus $em->persist($receivedObject) will always try to insert a new object. This will fail (due to the unique constraint of the id) if the ToDo-Entry already exists in the web app and needs to be updated.
Instead $em->merge($receivedObject) is used which automatically checks wether an insert or update is required.
Hot wo solve this?
Of course I could check for every received objects if an entity with the same ID already exists. In this case could load the existing object and update its properties manually. However this would be very cumbersome. The real project of course uses many different entities and each entity type/class would need its own handling to check which properties needs to be updated. Isn't there a better solution?
You can try to use registerManaged() method of Doctrine\ORM\UnitOfWork.
// $this->em <--- Doctrine Entity Manager
// $entity <--- detached Entity (and we know that this entity already exists in DB for example)
$id = [$entity->getId()]; //array
$data = $entity->toArray(); //array
$this->em->getUnitOfWork()->registerManaged($entity, $id, $data);
Of course, You can check the state of Your Entity using getEntityState() of Doctrine\ORM\UnitOfWork before/after perfoming needed actions.
$this->eM->getUnitOfWork()->getEntityState($entity, $assert = 3)
$assert <-- This parameter can be set to improve performance of entity state detection by potentially avoiding a database lookup if the distinction between NEW and DETACHED is either known or does not matter for the caller of the method.
While I have posted this question quite a while ago, it is still quite active. Until now my solution was to stick with Doctrine 2.9 and keep using the merge function. Now I am working on new project which should be Doctrine 3 ready and should thus not use the merge anymore.
My solution is of course specific for my special use case. However, maybe it is also useful for other:
My Solution:
As described in the question I use the merge method to sync deserialized, external entities into the web database where a version of this entity might already exist (UPDATE required) or not (INSERT required).
#Merge Annotation
In my case entities have different properties where some might be relevant for syncing and must be merged while others are only used for (web) internal housekeeping and must not be merged. To tell these properties appart, I have created a custom #Merge annotation:
use Doctrine\Common\Annotations\Annotation;
/**
* #Annotation
* #Target("PROPERTY")
*/
final class SyncMerge { }
This annotation is then be used to mark the entities properties which should be merged:
class ToDoEntry {
/*
* #Merge
*/
protected $date;
/*
* #Merge
*/
protected $title;
// only used internally, no need to merge
protected $someInternalValue;
...
}
Sync + Merge
During the sync process the annotation is used to merge the marked properties into existing entities:
public function mergeDeserialisedEntites(array $deserializedEntities, string $entityClass): void {
foreach ($deserializedEntities as $deserializedEntity) {
$classMergingInfos = $this->getMergingInfos($class);
$existingEntity = $this->entityManager->find($class, $deserializedEntity->getId());
if (null !== $existingEntity) {
// UPDATE existing entity
// ==> Apply all properties marked by the Merge annotation
foreach ($classMergingInfos as $propertyName => $reflectionProperty) {
$deserializedValue = $reflectionProperty->getValue($deserializedEntity);
$reflectionProperty->setValue($existingEntity, $deserializedEntity);
}
// Continue with existing entity to trigger update instead of insert on persist
$deserializedEntity = $existingEntity;
}
// If $existingEntity was used an UPDATE will be triggerd
// or an INSERT instead
$this->entityManager->persist($deserializedEntity);
}
$this->entityManager->flush();
}
private $mergingInfos = [];
private function getMergingInfos($class) {
if (!isset($this->mergingInfos[$class])) {
$reflectionClass = new \ReflectionClass($class);
$classProperties = $reflectionClass->getProperties();
$propertyInfos = [];
// Check which properties are marked by #Merge annotation and save information
foreach ($classProperties as $reflectionProperty) {
$annotation = $this->annotationReader->getPropertyAnnotation($reflectionProperty, Merge::class);
if ($annotation instanceof Merge) {
$reflectionProperty->setAccessible(true);
$propertyInfos[$reflectionProperty->getName()] = $reflectionProperty;
}
}
$this->mergingInfos[$class] = $propertyInfos;
}
return $this->mergingInfos[$class];
}
That's it. If new properties are added to an entity I have only to decide whether it should be merged or not and add the annotation if needed. No need to update the sync code.
Actually the code to handle this can be just a few lines. In background Doctrine will issue a query to search for your entity if not already in memory, so you can do the same by doing the query yourself with result cache enabled, and then just use PropertyAccessor to map the data.
https://symfony.com/doc/current/components/property_access.html
See this gist for a POC https://gist.github.com/stevro/99060106bbe54d64d3fbcf9a61e6a273
I'll preface this question with the following: I know there are a million posts on the internet about the old "An object with the same key already exists in the ObjectStateManager" issue. My scenario is a bit more complicated, I think.
I have a UnitOfWork class which creates a DbContext and passes it to any repository which is called. The pattern I'm using closely follows the Unit of Work tutorial on the ASP.NET site. Unlike the tutorial, my repositories take in Business entities, map them to data entities, and perform some CRUD action. My Business logic only works with Business entities. Here is what I'm trying to do in a sample Business Manager class:
_unitOfWork.Repository.Add(entity);
_unitOfWork.Save(); // context.SaveChanges() under the hood
...Perform some operations on the model...
_unitOfWork.Repository.Update(entity);
_unitOfWork.Save();
Here is a sample Update method from the repository:
public virtual void Update(entity)
{
var dataEntity = // map from business entity to data;
_context.Entry(dataEntity).State = EntityState.Modified;
}
It obviously fails on the last line. Here is where my confusion sets in:
The entity's State is Detached
When I attempt to change the State to Modified or Unchanged, it gives me the ObjectStateManager exception above.
When I attempt to detach the entity from the context (((IObjectContextAdapter)_context).ObjectContext.Detach(entity);) I get an exception about how the entity is not attached to the context, therefore, it cannot detach it. Very confusing (something fundamental I'm missing, for sure).
Many other posts suggest I make a database call, update that entity in the repository, then _unitOfWork.Save(). I don't like this approach. I shouldn't need to make an unnecessary network call to update an entity.
The Update method in the repository needs to handle two scenarios: 1) updating an entity which is not currently tracked by the context, and 2) updating an entity which IS currently tracked by the context. The second piece is what I'm struggling with.
Any help or insight is appreciated.
Thanks!
This means that there already is an object attached to the context with the same key as the new dataEntity. The existing object and the new entity both represent the same entry in the database but they are two different objects.
This may indicate that the lifespan of your _context is too long, but that's hard to judge from your code. It is certain though that the context was previously used to fetch an entity from the database that is subsequently duplicated by var dataEntity = ....
You may have to shorten the lifespan of the context, I can't tell. If you think it's OK you may want to use the Local collection to check whether the entity is already there. That will save the database round trip that Find may still make.
I found a hybrid solution which appears to work:
public virtual void Update(TB entity)
{
var dataEntity = Mapper.Map<TB, TD>(entity);
var pkey = _dbSet.Create().GetType().GetProperty("Id").GetValue(dataEntity);
var entry = _context.Entry(dataEntity);
if (entry.State == EntityState.Detached)
{
var attachedEntity = _dbSet.Find(pkey);
if (attachedEntity != null)
{
var attachedEntry = _context.Entry(attachedEntity);
attachedEntry.CurrentValues.SetValues(dataEntity);
}
else
{
entry.State = EntityState.Modified;
}
}
else
{
entry.State = EntityState.Modified;
}
}
My scenario:
This is an ASP.NET 4.0 web app programmed via C#
I implement a repository pattern. My repositorys all share the same ObjectContext, which is stored in httpContext.Items. Each repository creates a new ObjectSet of type E. Heres some code from my repository:
public class Repository<E> : IRepository<E>, IDisposable
where E : class
{
private DataModelContainer _context = ContextHelper<DataModelContainer>.GetCurrentContext();
private IObjectSet<E> _objectSet;
private IObjectSet<E> objectSet
{
get
{
if (_objectSet == null)
{
_objectSet = this._context.CreateObjectSet<E>();
}
return _objectSet;
}
}
public IQueryable<E> GetQuery()
{
return objectSet;
}
Lets say I have 2 repositorys, 1 for states and 1 for countrys and want to create a linq query against both. Note that I use POCO classes with the entity framework. State and Country are 2 of these POCO classes.
Repository stateRepo = new Repository<State>();
Repository countryRepo = new Repository<Country>();
IEnumerable<State> states = (from s in _stateRepo.GetQuery()
join c in _countryRepo.GetQuery() on s.countryID equals c.countryID
select s).ToList();
Debug.WriteLine(states.First().Country.country)
essentially, I want to retrieve the state and the related country entity. The query only returns the state data... and I get a null argument exception on the Debug.WriteLine
LazyLoading is disabled in my .edmx... thats the way I want it.
You're doing a join without retrieving anything from it. There are multiple solutions to your problem:
Use Include to load the dependent entities: from s in ((ObjectSet<State>) _stateRepo.GetQuery).Include("Country"). The problem with this approach is that you should expose the ObjectSet directly rather than as a IQueryable if you want to avoid casting.
Use context.LoadProperty(states.First(), s => s.Country) to explicitly load the Country from the database for a given state.
Select both entities in the query: from s in ... join c ... select new { s, c }. You won't be able to access directly the state's Country property but you have it in the anonymous type.
Enable lazy loading.
Your repository implementation is very similar to mine, especially the way you are storing the ObjectContext. It works fine for me, so I don't think it's a conceptual problem.
Try using a static objectcontext (no wrapper) just to see if that fixes the problem. Perhaps there is a bug in your ContextHelper which causes your context to get disposed and recreated.
I've been getting several errors:
cannot add an entity with a key that is already in use
An attempt has been made to attach or add an entity that is not new, perhaps having been loaded from another datacontext
In case 1, this stems from trying to set the key for an entity versus the entity. In case 2, I'm not attaching an entity but I am doing this:
MyParent.Child = EntityFromOtherDataContext;
I've been using using the pattern of wrap everything with a using datacontext. In my case, I am using this in a web forms scenario, and obviously moving the datacontext object to a class wide member variables solves this.
My questions are thus 2 fold:
How can I get rid of these errors and not have to structure my program in an odd way or pass the datacontext around while keeping the local-wrap pattern? I assume I could make another hit to the database but that seems very inefficient.
Would most people recommend that moving the datacontext to the class wide scope is desirable for web pages?
Linq to SQL is not adapted to disconnected scenarios. You can copy your entity to a DTO having a similar structure as the entity and then pass it around. Then copy the properties back to an entity when it's time to attach it to a new data context. You can also deserialize/reserialize the entity before attaching to a new data context to have a clean state. The first workaround clearly violates the DRY principle whereas the second is just ugly. If you don't want to use any of these solution the only option left is to retrieve the entity you're about to modify by its PK by hitting the DB. That means an extra query before every update. Or use another ORM if that's an option for you. Entity Framework 4 (included with .NET 4) with self-tracking entities is what I'm using currently on a web forms project and everything is great so far.
DataContext is not thread-safe and should only be used with using at the method level, as you already do. You can consider adding a lock to a static data context but that means no concurrent access to the database. Plus you'll get entities accumulated in memory inside the context that will turn into potential problems.
For those that came after me, I'll provide my own take:
The error "an attempt has been made to add or attach an entity that is not new" stems from this operation:
Child.Parent = ParentEntityFromOtherDataContext
We can reload the object using the current datacontext to avoid the problem in this way:
Child.Parent = dc.Entries.Select(t => t).Where(t => t.ID == parentEntry.ID).SingleOrDefault();
Or one could do this
MySubroutine(DataContext previousDataContext)
{
work...
}
Or in a web forms scenario, I am leaning to making the DataContext a class member such as this:
DataContext _dc = new DataContext();
Yes, the datacontext is suppose to represent a unit of work. But, it is a light-weight object and in a web forms scenario where a page is fairly transient, the pattern can be changed from the (using dc = new dc()) to simply using the member variable _dc. I am leaning to this last solution because it will hit the database less and require less code.
But, are there gotchas to even this solution? I'm thinking along the lines of some stale data being cached.
What I usually do is this
public abstract class BaseRepository : IDisposable
{
public BaseRepository():
this(new MyDataContext( ConfigurationManager.ConnectionStrings["myConnection"].ConnectionString))
{
}
public BaseRepository(MyDataContext dataContext)
{
this.DataContext = dataContext;
}
public MyDataContext DataContext {get; set;}
public void Dispose()
{
this.DataContext.Dispose();
}
}
Then imagine I have the following repository
public class EmployeeRepository : BaseRepository
{
public EmployeeRepository():base()
{
}
public EmployeeRepository(MyDataContext dataContext):base(dataContext)
{
}
public Employee SelectById(Guid id)
{
return this.DataContext.Employees.FirstOrDefault(e=>e.Id==id);
}
public void Update(Employee employee)
{
Employee original = this.Select(employee.Id);
if(original!=null)
{
original.Name = employee.Name;
//others
this.DataContext.SubmitChanges();
}
}
}
And in my controllers (I am using asp.net mvc)
public ActionResult Update(Employee employee)
{
using(EmployeeRepository employeeRepository = new EmployeeRepository())
{
if(ModelState.IsValid)
{
employeeRepository.Update(employee);
}
}
//other treatment
}
So the datacontext is properly disposed and I can use it across the same instance of my employee repository
Now imagine that for a specific action I want the employee's company to be loaded (in order to be displyed in my view later), I can do this:
public ActionResult Select(Guid id)
{
using(EmployeeRepository employeeRepository = new EmployeeRepository())
{
//Specifying special load options for this specific action:
DataLoadOptions options = new DataLaodOptions();
options.LoadWith<Employee>(e=>e.Company);
employeeRepository.DataContext.LoadOptions = options;
return View(employeeRepository.SelectById(id));
}
}