Can I restructure this query so I don't have to fetch from the database? I have tried various techniques, but none of them work.
public void Update(CartEntryViewModel entry)
using (var context = new MyContext())
{
User user = Auth.GetUser(context);
CartEntry model = context.CartEntries.Find(entry.Id);
// Change the item and update quantity
model.Item = context.Items.Find(entry.Item.Id);
model.Quantity = entry.Quantity;
context.Entries(model).EntityState = EntityState.Modified;
context.SaveChanges();
}
}
The Attach() method takes the model you already have and attaches it to the context as if it were just read from the DB. You just have to change the state so the context knows to update the corresponding row in the DB when SaveChanges() is called.
public void Update(CartEntryViewModel entry)
{
CartEntry model = new CartEntry
{
model.Id = entry.Id,
model.Item = entry.Item,
model.Quantity = entry.Quantity,
// Set other properties.
};
using (MyContext context = new MyContext())
{
context.CartEntries.Attach(model);
context.Entry(model).State = EntityState.Modified;
context.SaveChanges();
}
}
Related
I set up a Generic repository using this code for update
private void AttachIfNot(TEntity entityToActive)
{
if (_dbContext.Entry(entityToActive).State == EntityState.Detached)
{
_dbSet.Attach(entityToActive);
}
}
private void UpdateEntity(TEntity entityToUpdate)
{
AttachIfNot(entityToUpdate);
_dbContext.Entry(entityToUpdate).State = EntityState.Modified;
}
It just attach the entity and set the modified state to save.
But when I use efocre ownsone to map a value object,the update entity function is not working.
I found out that it only works when I set Valueobject to modified too.
_dbContext.Entry(entityToUpdate).State = EntityState.Modified;
_dbContext.Entry(entityToUpdate.Valueobject).State = EntityState.Modified;
But It is hard for me to specify all the value objects in a Generic Repository.
This is code also has problems with one to many or other relations.
The working way is like this:
Classroom classroom = new Classroom
{
Id = 1,
Name = "b",
Students = new List<Student>
{
new Student()
{
Name = "aa",
Id = 2
}
}
};
if (_defaultDbContext.Entry(classroom).State == EntityState.Detached)
{
_defaultDbContext.Classrooms.Attach(classroom);
foreach(var stu in classroom.Students)
{
_defaultDbContext.Students.Attach(stu);
}
}
_defaultDbContext.Entry(classroom).State = EntityState.Modified;
foreach (var stu in classroom.Students)
{
_defaultDbContext.Entry(stu).State = EntityState.Modified;
}
_defaultDbContext.SaveChanges();
I found out one way is get the entity form repo then update it using automapper:
targetEntity = repo.GetById(entityId);
automapper.map(souceEntity,targetEntity);
//or
automapper.map(souceDto,targetEntity);
_dbContext.Save();
The entity comes by query, so the change will be tracked.
But I have to configure the automapper with this entity map when I want to change entity
CreateMap<EntityType, EntityType>();
I think it's not the best solution. Is there a bettere way?
DbContext.Update would be fine to fix this problem.
see:
https://www.learnentityframeworkcore.com/dbcontext/change-tracker
Let's take this scenario:
I want to add a task to project.
The project exist already.
Task will be added as new entity and attached to the project.
A project can have one or many tasks.
This is the way I do it in now my repository :
public void AddTaskToProject(Project ProjectToUpdate,Task TaskToAdd)
{
using (var context = new myContext())
{
var project= context.Projects.First(x => x.Id == projectToUpdate.Id);
project.Tasks.Add(taskToAdd);
context.Tasks.Add(taskToAdd);
SaveContextChange(context);
}
}
Is there any other way to avoid as much call to database as I did?
The ideal for me, is to update the project, and then call only an update for the project entity ? is there a way to do that ?
This is the generic update I have:
public virtual void Update(params T[] items)
{
using (var context = new MyContext())
{
foreach (T item in items)
{
context.Entry(item).State =EntityState.Modified;
}
context.SaveChanges();
}
}
You can try:
public void AddTaskToProject(Project projectToUpdate,Task taskToAdd)
{
using (var context = new myContext())
{
var project = new Project() { ProjectId = projectToUpdate.Id };
context.Projects.Attach(project);
project.Tasks.Add(taskToAdd);
context.SaveChanges();
}
}
I'm using EF4. I'm adding a series of new entities from a list of DTOs, and I'm not saving changes until after all of them are added. I'm wanting to set the IDs of the DTOs to what the new entities' IDs are. How on earth do I do this? Does EF provide a mechanism for this?
With a single entity I would do this:
public void InsertMyDto(MyDto a_dto)
{
var newEntity = new MyEntity
{
Name = a_dto.Name,
Type = a_dto.Type.ToString(),
Price = a_dto.Price
};
_dataContext.MyEntities.AddObject(newEntity);
_dataContext.SaveChanges();
a_dto.ID = newEntity.ID;
}
This works fine, but what do I do in this case?
public void InsertMyDtos(IEnumerable<MyDto> a_dtos)
{
foreach (var myDto in a_dtos)
{
var newEntity = new MyEntity
{
Name = myDto.Name,
Type = myDto.Type.ToString(),
Price = myDto.Price
};
// Does some validation logic against the database that might fail.
_dataContext.MyEntities.AddObject(newEntity);
}
_dataContext.SaveChanges();
// ???
}
I want to save all at once, because I have validation work (not shown above) that is done against the database and fails before it gets to SaveChanges, and if it fails I want it to fail as a whole transaction (i.e. rollback).
I don't think that EF can help you here. It even can't help you for a single instance which forces you to write a_dto.ID = newEntity.ID. The counterpart of this code for multiple entites is to keep track of the pairs of dtos and new entities:
public void InsertMyDtos(IEnumerable<MyDto> a_dtos)
{
Dictionary<MyDto, MyEntity> dict = new Dictionary<MyDto, MyEntity>();
foreach (var myDto in a_dtos)
{
var newEntity = new MyEntity
{
Name = myDto.Name,
Type = myDto.Type.ToString(),
Price = myDto.Price
};
dict.Add(myDto, newEntity);
// Does some validation logic against the database that might fail.
_dataContext.MyEntities.AddObject(newEntity);
}
_dataContext.SaveChanges();
foreach (var item in dict)
item.Key.ID = item.Value.ID; // Key is MyDto, Value is MyEntity
}
I am inserting a record into the database, which looks like this:
class Transaction
{
int Id;
}
What I want, is when I insert this object, I want to create another record, like this:
class TransactionUpdate
{
int StartingTransactionId;
int EndingTransactionId;
}
What I have so far, is a loop in my SaveChanges on the DbContext, which takes new Transaction objects that will be created and creates TransationUpdate objects and attaches these to the DbContext.
public override int SaveChanges()
{
foreach(var entry in this.ChangeTracker.Entries())
{
if(entry.Entity is Transaction)
{
var update = new TransactionUpdate();
update.StartingTransactionId = ((Transaction)entry.Entity).PreviousTransactionId;
update.EndingTransactionId = ((Transaction)entry.Entity).Id; // This is zero because the entity has not been inserted.
this.TransactionUpdates.Add(update);
}
}
}
The problem is, I cannot properly create a TransactionUpdate because I do not have 'EndingTransactionId', or, the Id of the Transaction I am currently inserting.
How can I solve this problem?
Many Thanks.
SOLVED
I have done what Ladislav suggested and am now creating a list of items to add, along with references to the objects that are required to insert them. Thus:
public override int SaveChanges()
{
var transactionUpdatesToAdd = new List<Tuple<TransactionUpdate, Transaction>>();
foreach (var entry in this.ChangeTracker.Entries<Transaction>())
{
if (entry.State == EntityState.Added)
{
var update = new TransactionUpdate();
update.StartingTransactionId = ((Transaction)entry.Entity).PreviousTransactionId;
transactionUpdatesToAdd.Add(new Tuple<TransactionUpdate, Transaction>(update, entry.Entity));
}
}
using(var scope = new TransactionScope())
{
// Save new Transactions
base.SaveChanges();
// Update TransactionUpdates with new IDs
foreach (var updateData in transactionUpdatesToAdd)
{
updateData.Item1.EndingTransactionId = updateData.Item2.Id;
this.TransactionUpdates.Add(updateData.Item1);
}
// Insert the new TransactionUpdate entities.
return base.SaveChanges();
}
Based on your description I guess you are using autogenerated Id in database. You will not receive this Id befere executing SaveChanges on the context. You have to divide operation into two separate modifications:
public override int SaveChanges()
{
// call base context saving operation to insert all Transactions
base.SaveChanges();
foreach(var entry in this.ChangeTracker.Entries())
{
if(entry.Entity is Transaction)
{
var update = new TransactionUpdate();
update.StartingTransactionId = ((Transaction)entry.Entity).PreviousTransactionId;
update.EndingTransactionId = ((Transaction)entry.Entity).Id;
this.TransactionUpdates.Add(update);
}
}
// save changes again to insert all TransactionUpdates
base.SaveChanges();
}
You should wrap it into TransactionScope to perform whole saving as atomic operation.
If you haven't inserted TransactionId, you have it anyway in your object. Pass your object as parameter to an overloaded method SaveChanges and use it to pass the Id
I transfer data between the entity framework and the business layer and user layer by using Data Transfer Objects. I do have some doubt, if I retrieve an object which is converted to a DTO, how do I update the correct object in the entity framework and not just insert a duplicate?
The following code will update an EF 4 entity that has been created as a controller parameter in MVC from a strongly typed view:
It seems the trick is to use the ObjectStateManager to change the state from Added to Modified once the entity has been added to the context.
MyEntities db = new MyEntities();
db.Product.AddObject(product);
db.ObjectStateManager.ChangeObjectState(product, System.Data.EntityState.Modified);
return db.SaveChanges() > 0;
As per #Sean Mills comment if you are using EF5 use:
((IObjectContextAdapter) db).ObjectContext.ObjectStateManager.ChangeObjectState(entity, System.Data.EntityState.Added);
an old question, but just in case someone needs a code solution:
http://www.mikesdotnetting.com/Article/110/ASP.NET-MVC-Entity-Framework-Modifying-One-to-Many-and-Many-to-Many-Relationships
Example:
public void EditArticle(
Article article, string articleTypeId, string[] categoryId)
{
var id = 0;
Article art = de.ArticleSet
.Include("ArticleTypes")
.Include("Categories")
.Where(a => a.ArticleID == article.ArticleID)
.First();
var count = art.Categories.Count;
for (var i = 0; i < count; i++)
{
art.Categories.Remove(art.Categories.ElementAt(i));
count--;
}
foreach (var c in categoryId)
{
id = int.Parse(c);
Category category = de.CategorySet
.Where(ct => ct.CategoryID == id).First();
art.Categories.Add(category);
}
art.Headline = article.Headline;
art.Abstract = article.Abstract;
art.Maintext = article.Maintext;
art.DateAmended = DateTime.Now;
art.ArticleTypesReference.EntityKey = new EntityKey(
"DotnettingEntities.ArticleTypeSet",
"ArticleTypeID",
int.Parse(articleTypeId)
);
de.SaveChanges();
}
//I am replacing player :)
public ActionResult ProductEdit(string Id, Product product)
{
int IdInt = DecyrptParameter(Id);
MyEntities db = new MyEntities();
var productToDetach = db.Products.FirstOrDefault(p=> p.Id == IdInt);
if (product == null)
throw new Exception("Product already deleted"); //I check if exists, maybe additional check if authorised to edit
db.Detach(productToDetach);
db.AttachTo("Products", product);
db.ObjectStateManager.ChangeObjectState(product, System.Data.EntityState.Modified);
db.SaveChanges();
ViewData["Result"] = 1; // successful result
return View();
}
You would need to include a primary or alternate key in the DTO, then match that key back to the correct EF entity upon update.
This should work for EF 5: https://stackoverflow.com/a/11749716/540802:
db.Entry(product).State = EntityState.Modified;