Help me please resolve one problem.
I use Entity Framework for work with datebase.
My situation:
I have two tables which i need to fill. One of them must to contain identificator from the second table. Now I insert data to first table and make save changes. It give me identificator for the entity and I can to insert in second table the row with this identificator from first entity.
As a result, I have two save changes for my context. And I think that it's bad practice.
Code example:
var registration = new Registration()
{
//fill some properties
};
_registrationEntityService.Insert(registration);
context.SaveChanges();
var profile = new Profile()
{
//fill some properties
profile.RegId = registration.Id
};
_profileEntityService.Insert(profile);
context.SaveChanges();
How I can resolve this problem? Thanks.
EF assumes to use navigation properties like profile.Registration to resolve such problems:
var registration = new Registration()
{
//fill some properties
};
var profile = new Profile()
{
//fill some properties
profile.Registration = registration
};
context.SaveChanges();
Just ensure you generated the needed navigation property (it's generally based on foreign keys in your db). I highly recommend you to read any EF guide first http://www.entityframeworktutorial.net/EntityFramework5/add-entity-graph-using-dbcontext.aspx
Related
I'm new to EF and I've only worked with EF 6. When I use it to access the data from a database that I have already designed I don't see any method that allows me to manipulate data. To solve this temporarily I created some stored procedures for adding, deleting and updating data.
I would like to know if what I am doing is the right way to manipulate data in EF or not. In case it is not the right way how can I do this using the built in features of EF6. MSDN said there is an add object but couldn't find it.
There have been some changes in the API. EF6 does not use ObjectContext anymore, it uses a DbContext. This can be generated from a Database Model, or created using a Model first approach.
Old syntax:
objectContext.AddToUsers(user);
is now:
dbContext.Users.Add(user);
Here are some basic samples:
insert:
using(var dbContext = new MyDbContext())
{
var user = new User { ID=1, Name="Test" };
dbContext.Users.Add(user); // Add user
dbContext.SaveChanges(); // Save changes to DB
}
update:
using(var dbContext = new MyDbContext())
{
var user = dbContext.Users.Find(1);// find by ID = 1
user.Name = "New Name"; // Change name
dbContext.SaveChanges(); // Save changes to DB
}
delete:
using(var dbContext = new MyDbContext())
{
var user = dbContext.Users.Find(1);// find by ID = 1
dbContext.Users.Remove(user); // delete user
dbContext.SaveChanges(); // Save changes to DB
}
So, no need for stored procedures.. definetly not needed for simple CRUD.
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);
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.
Hi I use C# and EF 4.
I have two Entities CmsContent and CmsJob.
CmsJob has a navigational property to CmsContent.
I need add a CmsContent Object to CmsJob using the navigational property.
My code run with no error but I cannot persist the new entry om DataBase.
Could you tell me what I'm doing wrong?
Please provide me an example of code. Thanks for your support!
using (CmsConnectionStringEntityDataModel context = new CmsConnectionStringEntityDataModel())
{
CmsContent myContent = context.CmsContents.FirstOrDefault(x => x.ContentId == contentId);
CmsJob myJob = context.CmsJobs.FirstOrDefault(x => x.JobId == jobId);
myJob.CmsContents.Add(myContent);
}
Based on comments under #Hasan's answer you have incorrectly defined database. Your Job and Content are in many-to-many relation so you have junction table called CmsJobsContents but this table is missing primary key. Because of that it is read-only for EF and you cannot create new relations in your application. You must go to your database and mark both FKs in the CmsJobsContents as primary keys. After that update your model from database and you should be able to save changes.
That's because you haven't saved changes. Try this:
using (CmsConnectionStringEntityDataModel context = new CmsConnectionStringEntityDataModel())
{
CmsContent myContent = context.CmsContents.FirstOrDefault(x => x.ContentId == contentId);
CmsJob myJob = context.CmsJobs.FirstOrDefault(x => x.JobId == jobId);
myJob.CmsContents.Add(myContent);
context.SaveChanges();
}