Problem:
I need to save an updated detached EF object to the database.
The deatched entity is created through binding the base entity, then
foreach child ...
entity.children.add(child)
I add an Array of child entities that I also get from bind in controller.
What I want, is for the old entity to be completely replaced by the new entity, this means:
entity.property => update (easy)
entity.child => delete old child if not exists in the new,
update if already exists (easy),
or add if it doesnt exist already
What I have so far:
items tempitem = new items() { id = item.id };
_context.items.Attach(tempitem);
_context.items.ApplyCurrentValues(item);
foreach (var itemchild in item.children)
{
childEntity tempchild= new childEntity () { parentid = item.id };
_context.childEntity.Attach(tempchild);
_context.childEntity.ApplyCurrentValues(itemchild );
}
This lets me update base entity fine, and also update any existing entities fine.
It doesnt let me delete old entities - tried doing an
item.children.Clear()
but nothing happens, and also when I try to add a new child entity (that was bound to the detached) - nothing happens either.
This can't be too hard, can it? I'm thinking of turning to NHibernate where things seem less bloated and more straightforward but powerful...
Basically you must load the original object graph from the database (parent and all children, using Include for example), otherwise EF cannot know which children are new and which have been deleted. You have to add or delete the children then by comparing the loaded original child collection with the current collection in your detached entity.
An example how to do that is here: https://stackoverflow.com/a/5540956/270591
Related
I would like to extend an existing datamodel in Microstream with a new data object. E.g. I have Customers, with data records in Microstream, and I would like to add Vendors, with their own datastructure and data. As the database is not empty, I cannot start as if their is no data, however adding a list of Vendor to the dataroot doesn't seem to work. Microstream says the list is null when starting, which is correct, but I cannot add my new object to a null list. Can someone explain me how to add a vendor to my 'database' ?
You just need to add this List and store this object with the existing list again.
I received an answer from fh-ms # Microstream:
Hi, you are right, the vendors list is not present in the storage, so the field will be initialized with its default value (null).
There are several possibilities to introduce initial values to new fields.
One rather complex way would be to implement a Legacy Type Handler.
A far more simple one is just lazy initialization in your Customer type:
public List<Vendor> getVendors()
{
if(this.vendors == null)
{
this.vendors = new ArrayList<>()
}
return this.vendors;
}
And that works !
I have an object, Client, with a navigation property that is a list of Order objects. Whenever I retrieve a Client object, I include the list of Orders, with AsNoTracking().
public new IQueryable<Client> FindByConditionNoTracking(Expression<Func<Client, bool>> expression)
{
return this.ClientContext.Set<Client>().Include(s => s.Orders)
.Where(expression).AsNoTracking();
}
In my UpdateClient repository method, I take in a Client object. I then attempt to retrieve that original client from the database (using Include to get the child Orders), map the Client param to the original, and save to the database. Over here, I do not use AsNoTracking, because I specifically want the changes to be tracked.
public new void Update(Client client)
{
var id = client.ClientId;
var original = this.ClientContext.Clients.Include(s => s.Orders).Where(s => s.ClientId == id)
.FirstOrDefault<Client>();
original = _mapper.Map(client, original);
this.ClientContext.Update(original);
}
The error I am getting is that an instance of Order with the same key value is already being tracked. A few problems with that:
Wherever the Client and the child Orders are retrieved for the purposes of display I use AsNoTracking.
The only place where I retrieve without AsNoTracking is where I get the original within this very method.
The bug isn't with the parent property. If I was improperly retrieving the Client elsewhere, wouldn't I have this error with the Client id itself? But the error seems to be only with the navigation property.
All insight is appreciated!
If anyone else runs into this: Automapper, when mapping collections, apparently recreates the entire collection. I solved the above issue by using Automapper.Collections in my mapping configuration. Thanks to Mat J for the tip!
I am using Datamapper ORM 1.8.2.1 with CodeIgniter 2.1.0 and I have trouble accessing newly added related objects from within a parent.
I have a parent class like this:
class Virement extends DataMapper
{
var $has_many = array("lignevirement");
// ...
}
and a child class like this:
class LigneVirement extends DataMapper
{
var $has_one = array("virement");
// ...
}
In the user code, I instantiate this parent and add a few child objects:
$vrt = new Virement; // and do some inits on properties.
$vrt->save();
$lili = new LigneVirement; // do some inits also on properties.
$lili->save();
$vrt->save($lili);
$lili = new LigneVirement; // do some inits also on properties.
$lili->save();
$vrt->save($lili);
// ...
When I then count immediately after the added child objects, I get 0 :
echo $vrt->lignevirement->count();
... whereas taking a look in the database table shows that the parent record has been added, all the child records have been added, and they are correctly related with the parent record.
By the way, when I then try this workaround, I get the correct number of child rows:
$vrt = new Virement($vrt->id);
So what might be wrong with my code above ?
In my experience, Datamapper doesn't make related objects accessible immediately after a save. This includes displaying the properties of a related object; to follow on from your example, the following code will not display the ID of the $vrt object:
$vrt = new Virement;
$vrt->get_by_id(1);
$li = new LigneVirement;
$li->save($vrt);
echo $li->vrt->id;
However, if you redirect, or reload the page, and then reload the $li object, all related items will be available as expected.
If you really need to have related items immediately available, you can create a new related object and load it based on the _id value, as you suggest. Something like:
$vrt = new Virement;
$vrt->get_by_id(1);
$li = new LigneVirement;
$li->save($vrt);
$vrt_refresh = new Virement;
$vrt_refresh->get_by_id($li->vrt_id);
echo $vrt_refresh->id;
(Obviously the above code would be unnecessary, as you already know the ID of the $vrt object, but this is the general principle).
Incidentally, regarding the note in your comment about Datamapper using the same ID for two new objects, I'd avoid using the same variable name for both the objects; this will be unreliable in my experience. Instead, use different variable names, or (if this is unavoidable) take a look at the "Clear" method: http://datamapper.wanwizard.eu/pages/utility.html#clear .
I am having a problem with Entity Framework in my MVC 3 application. I have a users table, which is only ever populated with a new user row when a machine entity is created by a user that hasn't created any machines before, i.e. it only creates users it hasn't seen before. Each user belongs to a sector (division of the company) which also must be set before the user and the machine are saved. I have a default sector that new users are assigned to (so that this may be changed later on).
I have some code in my machine controller class for the creation of new machines that looks like this:
[HttpPost]
public ActionResult Create(Machine machine)
{
if (ModelState.IsValid)
{
// work out if the user exists in the database already
var users = userRepository.All.Where(u => u.Username == machine.User.Username);
if (users.Count() == 0)
{
// if the user entry doesn't exist we have to create it assigning a default sector
Sector defaultSector = null;
var defaultSectors = sectorRepository.All.Where(s => s.IsDefaultForNewUsers);
if (defaultSectors.Count() == 0)
{
// jebus! no default sector, so create one
defaultSector = new Sector() { Name = "Default", IsDefaultForNewUsers = true };
sectorRepository.InsertOrUpdate(defaultSector);
sectorRepository.Save();
}
else
{
defaultSector = defaultSectors.First();
}
machine.User.Sector = defaultSector;
}
else
{
machine.User = users.First();
}
machineRepository.InsertOrUpdate(machine);
machineRepository.Save();
return RedirectToAction("Index");
}
else
{
ViewBag.PossibleInstalledOS = installedosRepository.All;
ViewBag.PossibleLicenceTypes = licencetypeRepository.All;
ViewBag.PossibleUsers = userRepository.All;
return View();
}
}
[Edit] Here is the body of the InsertOrUpdate method from my Machine repository:
public void InsertOrUpdate(Machine machine)
{
if (machine.MachineId == default(int)) {
// New entity
context.Machines.Add(machine);
} else {
// Existing entity
context.Entry(machine).State = EntityState.Modified;
}
}
The problem I'm having with this code is that when I save the machine, it keeps creating a new user even though that user is already in the system. The line that finds the user works and retrieves the user as I would expect but entity framework doesn't seem to understand that I wish to use this user that I've found and not create a new one. So at the moment I have multiple identical users (except ID of course) in my users table. I want a one to many here so that multiple machines are owned by the same user.
Does anyone have any idea how I force entity framework to respect that there is already a user there that I want to tie the new machine to?
You didn't post the code for your InsertOrUpdate method but I suspect that that is where the problem is. I bet in that method at some point you do something equivalent to:
context.Machines.Add(machine);
When you call DbSet.Add (or change the state of an entity to Added) you are actually adding the whole graph to the context. This process will stop when it encounters an object that is being tracked by the context. So if you have a machine object that references a user object and neither of these objects are being tracked by the context, then both the machine object and the user object will be added to the context and end up in an Added state. EF will then insert them both as new rows in the database.
What you need to do, which was alluded to in the other answer, is make sure than EF knows that an existing user object does exist in the database by making sure it's state is Unchanged (or possibly Modified) and not Added when you save.
There are various ways that you could accomplish this and it's hard to know which is best for you without seeing more of how your app and repository work. One way is to make sure that the context used to query for the user is the same context as is used to save. This way EF will already be tracking the existing user object and will know not to add it when you call Add.
Another way is to let your repository know somehow whether or not the user object is new. Often people use the primary key to determine this--a zero key indicates a new object, non-zero indicates an existing object. You could also pass a flag into your repository.
You can then call Add to add the graph, but then set the state of the User object to Unchanged (or Modified if it might have been changed since it was queried) if it is an existing user. This will prevent EF from inserting a new user into the database.
Can you double check that your repositories are using the same data context? If not, you are essentially adding a new User entity to the machineRepository. Alternatively you could attach the user to the context for the machine repository, but you'll likely keep running into bugs like this.
A majority of the examples I see now are either using the Code First Approach or using an older version of MVC and the Entity Framework.
Assume I have a movie to update and I get to the Edit View, in the Edit method with the Post verb, what is the proper way to update a Movie? The first Edit Method below gets me to the Edit View with the populated Movie values and the second one is the one I want to use to update, I have tried some things, but nothing updates the data.
public ActionResult Edit(int id)
{
var movie = (from m in _db.Movies1
where m.Id == id
select m).First();
return View(movie);
}
[HttpPost]
public ActionResult Edit(Movie movie)
{
try
{
// TODO: Add update logic here
//What do I need to call to update the entity?
_db.SaveChanges();
return RedirectToAction("Index");
}
catch
{
return View();
}
}
Assuming that _db is derived from ObjectContext you have two options:
Change the state of the entity to Modified:
_db.Movies1.Attach(movie);
_db.ObjectStateManager.ChangeObjectState(movie, EntityState.Modified);
_db.SaveChanges();
This marks all properties of movie as modified and will send an UPDATE statement to the database which includes all column values, no matter if the values really changed or not.
Reload the original entity from the database and apply the changes to it:
var originalMovie = (from m in _db.Movies1
where m.Id == movie.Id
select m).First();
// You actually don't need to assign to a variable.
// Loading the entity into the context is sufficient.
_db.Movies1.ApplyCurrentValues(movie);
_db.SaveChanges();
ApplyCurrentValues will mark only those properties as modified which really did change compared to the original and the UPDATE statement which will be sent to the database only includes the changed column values. So, the UPDATE statement is potentially smaller than in the first example but you have to pay the price to reload the original entity from the database.
Edit
How does the second code example work?
When you run a query using the context (_db) Entity Framework does not only retrieve the entity from the database and assign it to the left side of the query (originalMovie) but it actually stores a second reference internally. You can think of this internal context "cache" as a dictionary of key-value pairs - the key is the entity primary key and the value is the entity itself, the same object as originalMovie refers to.
ApplyCurrentValues(movie) looks up this entity in the context's internal dictionary: It takes the key property value Id of the passed in movie, searches for an entity with that key in the internal dictionary and then copies property by property from the passed in ("detached") movie to the internal ("attached") entity with the same key. EF's change tracking mechanism marks the properties as Modified which were actually different to create later the appropriate UPDATE statement.
Because of this internal reference to the original entity you do not need to hold your own reference: That's the reason why originalEntity is not used in the code. You can in fact remove the assignment to the local variable altogether.
The example would not work if you disable change tracking when you load the original entity - for example by setting _db.Movies1.MergeOption = MergeOption.NoTracking;. The example relies on enabled change tracking (which is the default setting when entities are loaded from the database).
I cannot say which of the two examples has better performance. That might depend on details like size of the entities, number of properties which have been changed, etc.
It's worth to note though that both approaches do not work if related entities are involved (for example movie refers to a category entity) and if the relationship or the related entity itself could have been changed. Setting the state to Modified and using ApplyCurrentValues both affect only scalar and complex properties of movie but not navigation properties.
Your second edit method should look something like this:
[HttpPost]
public ActionResult Edit(int id, FormCollection collection)
{
var movie = (from m in _db.Movies1
where m.Id == id
select m).First();
if (TryUpdateModel(movie))
{
_db.SaveChanges();
return (RedirectToAction("Index"));
}
return View(movie);
}