I have the following piece of code
private void DoAddPropertyType()
{
var ctx = Globals.DbContext;
var propType = new PropertyType()
{
ID = Guid.NewGuid(),
Name = "NewType",
Description = "New Property Type",
ModifiedDate = DateTime.Now
};
ctx.AddToPropertyTypes(propType);
PropertyTypes.Add(propType);
}
Globals.DbContext provides a static reference to the objectcontext initiated on startup. For some reason the ctx.AddToPropertyTypes(propType); bit does not add the entity to the context. If I breakpoint after that line and browse the ctx.PropertyTypes entity set it is not there. Any ideas?
EDIT 1:
If I add a ctx.SaveChanges() after the ctx.AddToPropertyTypes(propType) and step the actual adding appears to happen only once SaveChanges execute. This however does not suit my requirements as I want to first validate objects prior to saving and wanted to iterate through the entities in the entity set. Does any one know of an alternative approach?
So that is the point of your issue. ctx.PropertyTypes is not a real collection - it is entrance to the database and your "browsing" actually executes query to the database where your new object was not yet stored. If you want to find a new object added to the context without saving it first you must search the object inside the ObjectStateManager:
var entity = ctx.ObjectStateManager
.GetObjectStateEntries(EntityState.Added)
.Where(e => !e.IsRelationship)
.Select(e => e.Entity)
.OfType<PropertyType>()
.SingleOrDefault(p => p.ID == ...);
Related
I am making a simple editor on a web server that lets user change/add data to a single table stored on a MS SQL server.
I am using Entity Framework 6 to do this, and I am wondering how I should do to track the changes made to the entity model.
I would have hoped that I could load new data in the context, and have the context automatically diff against what's in the DB, and then call SaveChanges().
But from what I read online, it looks like I need to loop through all the data, and check myself what changed, so that I can then call Context.Entry(myEntry).State = Added or Context.Entry(myEntry).State = Modified
Is there no way for EF to automatically detect what's new, what's modified and what's unchanged?
I would recommend passing ViewModels or DTOs to the view, then map them back to the reloaded entity on a commit. EF will automatically only update values that change when setting values. Setting a value without changing the value will not trigger an update. (Where attaching an entity, and setting it's modified state will update all columns) Passing entities, while convenient, exposes more about your data structure than your UI may present, and can be tampered with before being sent back. Never trust anything coming back from the client. When serialized to a client, the data is no longer an entity, it is a JSON block of data. When sent back to the server, it isn't a tracked entity, it is a POCO with the entity's signature. No change tracking that EF entities can provide will apply on the client or survive serialization/deserialization.
For example:
Given a Child that has a name and birth date. We select a DTO to pass to the view. The view changes a name, we get the DTO back and copy all values, modified or otherwise back into the entity and call SaveChanges()
// For example, loading the child in the controller to pass to the view...
ChildDTO childDto = null;
using (var context = new TestDbContext())
{
childDto = context.Children
.Select(x => new ChildDto
{
ChildId = x.ChildId,
Name = x.Name,
BirthDte = x.BirthDate
}).Single(x => x.ChildId == 1);
}
// View updates just the name...
childDto.Name = "Luke";
// Example if the view passed DTO back to controller to update...
using (var context = new TestDbContext())
{
var child = context.Children.Single(x => x.ChildId == 1);
child.Name = childDto.Name;
child.BirthDate = childDto.BirthDate;
context.SaveChanges();
}
If the name changed and the birth date did not, the EF generated update statement would only update the Name. If the entity name was already "Luke", then no Update statement would be issued. You can verify this behavior with an SQL profiler to see if/when/what SQL EF sends to the database.
Automapper can help simplify this for getting the DTO back into the entity:
var mappingConfig = new MapperConfiguration(cfg =>
{
cfg.CreateMap<Child, ChildDTO>();
cfg.CreateMap<ChildDTO, Child>();
});
Then when reading, leverage ProjectTo instead of Select:
using (var context = new TestDbContext())
{
childDto = context.Children
.ProjectTo<ChildDTO>(mappingConfig)
.Single(x => x.ChildId == 1);
}
... and when updating the entity:
using (var context = new TestDbContext())
{
var child = context.Children.Single(x => x.ChildId == 1);
var mapper = mappingConfig.CreateMapper();
mapper.Map(childDto, child); // copies values from DTO to the entity instance.
context.SaveChanges();
}
It's important to validate the DTO prior to copying values across to the Entity, whether doing it manually or with Automapper. Automapper config can also be set up to only copy over values that are expected/allowed to change.
I want to use EF DbContext/POCO entities in a detached manner, i.e. retrieve a hierarchy of entities from my business tier, make some changes, then send the entire hierarchy back to the business tier to persist back to the database. Each BLL call uses a different instance of the DbContext. To test this I wrote some code to simulate such an environment.
First I retrieve a Customer plus related Orders and OrderLines:-
Customer customer;
using (var context = new TestContext())
{
customer = context.Customers.Include("Orders.OrderLines").SingleOrDefault(o => o.Id == 1);
}
Next I add a new Order with two OrderLines:-
var newOrder = new Order { OrderDate = DateTime.Now, OrderDescription = "Test" };
newOrder.OrderLines.Add(new OrderLine { ProductName = "foo", Order = newOrder, OrderId = newOrder.Id });
newOrder.OrderLines.Add(new OrderLine { ProductName = "bar", Order = newOrder, OrderId = newOrder.Id });
customer.Orders.Add(newOrder);
newOrder.Customer = customer;
newOrder.CustomerId = customer.Id;
Finally I persist the changes (using a new context):-
using (var context = new TestContext())
{
context.Customers.Attach(customer);
context.SaveChanges();
}
I realise this last part is incomplete, as no doubt I'll need to change the state of the new entities before calling SaveChanges(). Do I Add or Attach the customer? Which entities states will I have to change?
Before I can get to this stage, running the above code throws an Exception:
An object with the same key already exists in the ObjectStateManager.
It seems to stem from not explicitly setting the ID of the two OrderLine entities, so both default to 0. I thought it was fine to do this as EF would handle things automatically. Am I doing something wrong?
Also, working in this "detached" manner, there seems to be an lot of work required to set up the relationships - I have to add the new order entity to the customer.Orders collection, set the new order's Customer property, and its CustomerId property. Is this the correct approach or is there a simpler way?
Would I be better off looking at self-tracking entities? I'd read somewhere that they are being deprecated, or at least being discouraged in favour of POCOs.
You basically have 2 options:
A) Optimistic.
You can proceed pretty close to the way you're proceeding now, and just attach everything as Modified and hope. The code you're looking for instead of .Attach() is:
context.Entry(customer).State = EntityState.Modified;
Definitely not intuitive. This weird looking call attaches the detached (or newly constructed by you) object, as Modified. Source: http://blogs.msdn.com/b/adonet/archive/2011/01/29/using-dbcontext-in-ef-feature-ctp5-part-4-add-attach-and-entity-states.aspx
If you're unsure whether an object has been added or modified you can use the last segment's example:
context.Entry(customer).State = customer.Id == 0 ?
EntityState.Added :
EntityState.Modified;
You need to take these actions on all of the objects being added/modified, so if this object is complex and has other objects that need to be updated in the DB via FK relationships, you need to set their EntityState as well.
Depending on your scenario you can make these kinds of don't-care writes cheaper by using a different Context variation:
public class MyDb : DbContext
{
. . .
public static MyDb CheapWrites()
{
var db = new MyDb();
db.Configuration.AutoDetectChangesEnabled = false;
db.Configuration.ValidateOnSaveEnabled = false;
return db;
}
}
using(var db = MyDb.CheapWrites())
{
db.Entry(customer).State = customer.Id == 0 ?
EntityState.Added :
EntityState.Modified;
db.SaveChanges();
}
You're basically just disabling some extra calls EF makes on your behalf that you're ignoring the results of anyway.
B) Pessimistic. You can actually query the DB to verify the data hasn't changed/been added since you last picked it up, then update it if it's safe.
var existing = db.Customers.Find(customer.Id);
// Some logic here to decide whether updating is a good idea, like
// verifying selected values haven't changed, then
db.Entry(existing).CurrentValues.SetValues(customer);
I have this entity, want to update using entityframework
EmployeeModel employee = new EmployeeModel
{
Id = 1000, //This one must
FirstName = modifiedValue,
Email = modifiedValue,
LastName = originalValue,
Phone = originalValue
};
Code to update
_db.ObjectStateManager.ChangeObjectState(employee, EntityState.Modified);
_db.SaveChanges();
This is the SQL statement got once updated
Update Employee set Id=1138,FirstName='modifiedValue',Email='modifiedValue',LastName= 'OriginalValue',phone='originalValue' where Id=1138
But I am expecting this
Update Employee set FirstName='modifiedValue', Email='modifiedValue' where Id=1138.
I dont know what I am missing here. Please let me know.
This problem is common when dealing with DTOs. An employee entity is fetched from the database, mapped to a DTO and sent over the wire. The client then modifies this DTO and sends it back to the server.
When you touch (set) a property on an EF entity, EF will assume that the value has been changed. Even if the old value and the new value are exactly the same.
The same problem occurs when you map the DTO to a new Entity and attach it to EF and updating its status to 'Modified'.
Using AutoMapper:
// This will result in the full update statement
var employee = AutoMapper.Mapper.Map<EmployeeDto, Employee>(dto);
// This will result in a smaller update statement (only actual changes)
var employee = dbContext.Employees.Find(dto.Id);
AutoMapper.Mapper.Map(dto, employee);
Or, manually (I would avoid doing this, but just for the sake of completeness):
// This will result in a smaller update statement (only actual changes)
var employee = dbContext.Employees.Find(dto.Id);
if (employee.Email != dto.Email )
employee.Email = dto.Email;
There are probably some other ways for dealing with this problem... but using AutoMapper together with Entity Framework correctly is definitely one of the easiest ways.
This is the solution I got
var entity = _db.CreateObjectSet<Employee>();
entity.Detach(employee);
entity.Attach(employee);
foreach (string modifiedPro in employeeModel.ModifiedProperties){
_db.ObjectStateManager.GetObjectStateEntry(employee).SetModifiedProperty(modifiedPro);}
_db.SaveChanges();
Only modified values in the sql update statement
Update Employee set FirstName='modifiedValue', Email='modifiedValue' where Id=1138.
If anybody knows better answer than this, Please post your suggestions
You can try this way
public update(Person model)
{
// Here model is model return from form on post
var oldobj = db.Person.where(x=>x.ID = model.ID).SingleOrDefault();
var UpdatedObj = (Person) Entity.CheckUpdateObject(oldobj, model);
db.Entry(oldobj).CurrentValues.SetValues(UpdatedObj);
}
public static object CheckUpdateObject(object originalObj, object updateObj)
{
foreach (var property in updateObj.GetType().GetProperties())
{
if (property.GetValue(updateObj, null) == null)
{
property.SetValue(updateObj,originalObj.GetType().GetProperty(property.Name)
.GetValue(originalObj, null));
}
}
return updateObj;
}
Here's what I'd like to do:
var myCustomer = new Customer();
myCustomer.Name = "Bob";
myCustomer.HasAJob = true;
myCustomer.LikesPonies = false;
Then I'd like to pass it into an update method:
public UpdateCustomer(Customer cust)
{
using(var context = dbcontext())
{
var dbCust = context.Customers.FirstOrDefault(c => c.Name == cust.Name);
if(dbCust != null)
{
// Apply values from cust here so I don't have to do this:
dbCust.HasAJob = cust.HasAJob;
dbCust.LikesPonies = cust.LikesPonies
}
context.SaveChanges();
}
}
The reason for this is I'm working in multiple different parts of my application, and/or across DLLs. Is this possible?
EDIT: Found this question to be immensely useful:
Update Row if it Exists Else Insert Logic with Entity Framework
If you are sure that the entity is in the database and you have key you would just Attach the object you have to the context. Note that attached entities are by default in Unchanged state as the assumption is that all the values of properties are the same as in the database. If this is not the case (i.e. values are different) you need to change the state of the entity to modified. Take a look at this blog post: http://blogs.msdn.com/b/adonet/archive/2011/01/29/using-dbcontext-in-ef-feature-ctp5-part-4-add-attach-and-entity-states.aspx it describes several sceanrios including the one you are asking about.
I'm working on a MVC3 application and i'm using the Entity Framework linked to an Oracle database (11G R2).
I'm encountering an issue when i'm trying to use a single object context inside a TransactionScope.
Here is the code :
using (TransactionScope scope = new TransactionScope())
{
using (Entities context = new Entities())
{
// Right insert
T_RIGRIGHT entity1 = new T_RIGRIGHT()
{
RIGCODE = "test1",
RIGINSERTLOGIN = "aco",
RIGINSERTDATE = DateTime.Now,
RIGUPDATELOGIN = "aco",
RIGUPDATEDATE = DateTime.Now
};
context.AddToT_RIGRIGHT(entity1);
context.SaveChanges();
// Right/Profile insert
T_RIPRIGHTPROFILE entity2 = new T_RIPRIGHTPROFILE()
{
PROID = 3,
RIGID = entity1.RIGID,
RIPINSERTLOGIN = "aco",
RIPINSERTDATE = DateTime.Now,
RIPUPDATELOGIN = "aco",
RIPUPDATEDATE = DateTime.Now
};
context.AddToT_RIPRIGHTPROFILE(entity2);
context.SaveChanges(); // SaveChanges fails due to the FK constraint on table
}
scope.Complete();
}
Let me explain the code...
First I create an entity called entity1 as a T_RIGRIGHT element.
The I instanciate a T_RIPRIGHTPROFILE element that uses the id of the T_RIGRIGHT element created before.
The execution fails on the second context.SaveChanges() and the exception concerns the Foreign Key constraint on the table T_RIPRIGHTPROFILE (requires a T_RIGRIGHT).
Hope my explanations are clear enough
Is there any way to make it works ?
P.S. : I apologize for my english as it's not my native language.
You are trying to assign the FK entity1.RIGID of an entity that has not been committed to the DB:
RIGID = entity1.RIGID,
If you look at entity1 closely you will see that RIGID is 0 by default - instead you should set the navigation property representing the FK relationship:
RIG = entity1,
This will enable EF to properly relate these entities, for this entity1 does not have to be committed to the DB yet, so you do not even need the extra SaveChanges() call.
Also in your scenario you do not need a TransactionScope - EF uses a transaction internally already in SaveChanges() - based on the suggested changes you only need one SaveChanges() call and hence no outer transaction scope is needed.