I'm using guids as PK for my entities.
As EF doesn't support the newid() SQL statement, I force a Guid.NewGuid() in my creation methods.
Here is my problem :
I've a table with a clustered unique constraint (2 strings, not PK).
I'm running some code in the same EF context which perfoms operations and adds/links entities, etc.
Is it possible to search for an entity in 'Added' state in my context ? ; that is to say which is in my context, but not yet inserted in my DB.
To avoid the raising of the SQL unique constraint, I have to know if the entity is already 'queued' in the context, and to re-use it instead of creating a new Guid (... and a different entity! :( )
this post saved me :) :
Link
var stateEntries = context.ObjectStateManager.GetObjectStateEntries(EntityState.Added | EtityState.Modified | EntityState.Unchanged);
var roleEntityEntries = stateEntries.Select(s => s.Entity).OfType<Role>();
roleEntity = roleEntityEntries.FirstOrDefault(r => r.RoleName.Trim().ToLower() == roleName.Trim().ToLower());
if (roleEntity == null)
{
return new Role { RoleName = roleName };
}
Related
I am working on a mechanism to seed a collection of tables via EF Core. How can I sort a DbContext's entities in order of foreign key dependencies? Since some tables have foreign keys, some tables need to be seeded before others. It seems like there would be a simple API for performing this sort, but all I have been able to find are a couple complex recursive T-SQL implementations.
I am sure there is a common solution for this type of problem that is prevalent, I just have been unable to locate it / know how to search for it.
Update:
Because EF Core doesn't seem to support Merge/Upsert/AddOrUpdate yet, I am going down the path of a database-specific (MySQL family in this case) raw SQL query. So, I have a method like below that I want to call for a collection of entities, but I need to call this method in order of the TEntityType's foreign key dependencies. Since it is a raw SQL query and not an EF API, per se, I don't think EF can auto-magically update tables in the correct dependency order (in response to #Gert's comment).
private static void InsertOnDuplicateKeyUpdate<TEntityType>(DbContext dbContext) where TEntityType : class
{
var entityType = dbContext.Model.FindEntityType(typeof(TEntityType));
var properties = GetPropertiesLessValueGeneratedTimestamps(entityType);
var columns = string.Join(", ", properties.Select(x => x.Name));
var values = CreateValues<TEntityType>(properties);
var updates = CreateUpdates(properties);
var rawSqlString = "INSERT INTO " + entityType.Relational().TableName + " (" + columns + ") VALUES " +
values + " ON DUPLICATE KEY UPDATE " + updates;
dbContext.Set<TEntityType>().FromSql(rawSqlString);
dbContext.SaveChanges();
}
Entity Framework Core contains all information needed to sort entity types based on foreign key dependencies. The only issue I found when using EF Core as a source of table order is that same table references will need to be handled differently - whether it might be for example allowing inserting identifiers, disabling table triggers or some other way.
To grab a list of entity types from which you can get table names, DbSet etc, use the following function:
private IList<IEntityType> GetDependentTables(IModel model)
{
var copied = new List<IEntityType>();
var tables = model.GetEntityTypes().Where(x => x.GetKeys().Any()).ToList();
while (tables.Count > 0)
{
var copiedCount = copied.Count;
for (var i = 0; i < tables.Count; i++)
{
var table = tables[i];
if (table.GetForeignKeys().All(x => copied.Contains(x.PrincipalEntityType) || x.DeclaringEntityType == x.PrincipalEntityType))
{
copied.Add(table);
tables.RemoveAt(i);
break;
}
}
if (copiedCount == copied.Count)
{
throw new InvalidOperationException("Circular foreign keys found in remaining tables: " + string.Join(",", tables.Select(x => x.Name)));
}
}
return copied.Where(x => x.BaseType == null).ToList();
}
usage:
var tableEntityTypes = GetDependentTables(myDbContext.Model);
Apparently, EF6 doesn't like objects that have multiple foreign key properties that use the same key value, but do not share the same reference. For example:
var user1 = new AppUser { Id = 1 };
var user2 = new AppUser { Id = 1 };
var address = new Address
{
CreatedBy = user1, //different reference
ModifiedBy = user2 //different reference
};
When I attempt to insert this record, EF throws this exception:
Saving or accepting changes failed because more than one entity of type
'AppUser' have the same primary key value. [blah blah blah]
I've discovered that doing this resolves the issue:
var user1 = new AppUser { Id = 1 };
var user2 = user1; //same reference
I could write some helper code to normalize the references, but I'd rather EF just know they're the same object based on the ID alone.
As for why EF does this, one explanation could be that its trying to avoid doing multipe CRUD operations on the same object since separate instances of the same entity could contain different data. I'd like to be able to tell EF not to worry about that.
Update
So it's as I suspected per my last paragraph above. In absense of a means to tell EF not to do CRUD on either instance, I will just do this for now:
if (address.ModifiedBy.Id == address.CreatedBy.Id)
{
address.ModifiedBy = address.CreatedBy;
}
Works well enough so long as I am not trying to do CRUD on either.
Update2
I've previously resorted to doing this to prevent EF from validating otherwise-required null properties when all I need is the child entity's ID. However, it doesn't keep EF from going into a tizzy over separate instances with the same ID. If it's not going to do CRUD on either AppUser object, why does it care if the instances are different?
foreach (var o in new object[] { address.ModifiedBy, address.CreatedBy })
{
db.Entry(o).State = EntityState.Unchanged;
}
If you get AppUser from context, then you will not need to do anything, because Entity Framework will track entities:
var user1 = context.AppUsers.Find(1);
var user2 = context.AppUsers.Find(1);
var address = new Address
{
CreatedBy = user1, //different reference
ModifiedBy = user2 //different reference
};
Now, they both will point to same objects and will not cause to conflict.
You can add two extra properties to have the Id for the main objects which is the AppUser, then you can use only one AppUser object and reference it for both the created and modified by properties.
CreatedById = user1.Id,
ModifiedById = user1.Id
Otherwise, your code will end up by saving two instances of AppUser with the same primary key.
Another approach is to set both the foreign key properties to only one AppUserobject
The explanation is that EF's change tracker is an identity map. I.e. a record in the database is mapped to one, and only one, CLR object.
This can be demonstrated easily by trying to attach two objects with the same key:
context.AppUsers.Attach(new AppUser { Id = 1 });
context.AppUsers.Attach(new AppUser { Id = 1 });
The second line will throw an exception:
Attaching an entity of type 'AppUser' failed because another entity of the same type already has the same primary key value.
This also happens if you assign
CreatedBy = user1, //different reference
ModifiedBy = user2 //different reference
Somewhere in the process, user1 and user2 must be attached to the context, giving rise to the exception you get.
Apparently, you have a function that receives two Id values that can be different or identical. Admittedly, it would be very convenient if you could simply create two AppUser instances from these Ids, not having to worry about identical keys. Unfortunately, your solution ...
if (address.ModifiedBy.Id == address.CreatedBy.Id)
... is necessary. Solid enough, though.
I have an Entity. Mandate. Every mandate has a required:many relation to a Person (NavigationProperty). I use the DbContext API with (LazyLoadingEnabled, AutoDetectChangesEnabled, ValidateOnSaveEnabled, ProxyCreationEnabled)
Now I like to delete a Mandate entity. The mandate entities are loaded by another context with AsNoTracking().
message.Result.
ObserveOn(On<DataComposition>.Scheduler).
Where(r => r).
Subscribe(_ =>
{
using (var unit = UnitOfWork.Begin())
{
var mandate = this.SelectedItem.OriginalEntity;
this.mandateRepository.Attach(mandate);
// mandate.Person.ToString();
this.mandateRepository.Delete(mandate);
unit.Commit();
}
this.List.RemoveOnUi(this.SelectedItem);
});
Now during committing I get the following exception: Entities in 'CodeFirstContainer.Mandates' participate in the 'Mandate_Person' relationship. 0 related 'Mandate_Person_Target' were found. 1 'Mandate_Person_Target' is expected.
The delete works if I include the Person Property during the population/selection or if I visit the Property (lazyloading), but I DONT LIKE to materialize/hold many entities only for the deletion case and I DONT LIKE to trigger more than a single DELETE query to db!
The fact that, if you have the navigation property mandate.Person populated, the following SQL statement ...
delete [dbo].[Mandates]
where (([Id] = #0) and ([PersonId] = #1))
... is sent to the database, lets me think that the navigation property indeed must be populated with a person with the correct PersonId to delete the parent.
I have no idea why Entity Framework just doesn't send a delete statement with the primary key ...
delete [dbo].[Mandates]
where ([Id] = #0)
... as I had expected.
Edit
If the Mandate entity has a foreign key property PersonId for the Person navigation property, the expected SQL (the second above) is sent to the database. In this case the Person navigation property can be null and the value of the FK property PersonId doesn't matter.
Edit 2
If you don't want to introduce a FK property the way with the least DB-roundtrip-costs would probably be to fetch the person's Id and then create a dummy person with that key in memory:
// ...
var personId = context.Mandates
.Where(m => m.Id == mandate.Id)
.Select(m => m.Person.Id)
.Single();
mandate.Person = new Person { Id = personId };
this.mandateRepository.Attach(mandate);
this.mandateRepository.Delete(mandate);
// ...
I am trying to achieve the following using Entity framework 4.0 and self-tracking entities:
1) The client application request a book form the server by providing an ISBN number
2) The server performs a query on its database to see if the book is already present
3a) If the book is in the database, it returns it.
3b) If the book is not in the database, it will query Amazon for info, extract the required attributes, create a new book, store it in the database, and return it to the client
Now, 3b) is where the problems are... I can't find any information on how I can create an entity object (a book) on the server side, add it to the context and store it in the database. I have tried all sorts of things:
public class BookBrowserService : IBookBrowserService {
public Book GetBook(string ISBN) {
using (var ctx = new BookBrowserModelContainer()) {
Book book = ctx.Books.Where(b => b.ISBN == ISBN).SingleOrDefault();
if (book == null) {
book = new Book();
book.ISBN = ISBN; // This is the key
book.Title = "This title would be retrieved from Amazon";
Author author = new Author();
author.Name = "The author's name would be retrieved from Amazon";
book.Authors.Add(author);
ctx.Books.AddObject(book);
ctx.SaveChanges(); // This one always throws an exception...
}
return book;
}
}
}
Could anyone tell me what I am doing wrong?
It looks like the problem is related to the EDMX model.
I have a Book entity and an Author entity, with a many-to-many relationship.
The Book entity's Key is ISBN, which is a string of Max length 13.
StoreGeneratedPattern is set to None.
The Author entity's Key is Id, which is a Guid.
StoreGeneratedPattern is Identity.
The exception message is:
"Cannot insert the value NULL into column 'Id', table 'BookBrowser.dbo.Authors'; column does not allow nulls. INSERT fails. The statement has been terminated. "
But since StoreGeneratedPattern is set to Identity, shouldn't an Id value be created automatically?
Thanks,
Peter
It looks that the problem was that I used a Guid as Key in combination with StoreGeneratedPattern = Identity.
When I set StoreGeneratedPattern to None and create my own Guid using Id = Guid.NewGuid(), the problem is gone.
Apparently, the SQL server cannot generate Guids...
you can use StoreGeneratedPattern=Identity, but generated sql script based on your edmx doesn`t contain newid() in describing primary key(GUID). you can do this manually in generated sql script. 'BookId uniqueidentifier NOT NULL
DEFAULT newid()'. So id value will create GUID automatically.
Let's say I have a Person class and an Order class, with foreign keys in the DB. The EF model will mark Person with a List of Orders and Order with a Person instance.
If I want to set the Person for the Order, do I really have to do it with an instance of Person?
Is there not a slimmed down way to do so, say with just a PersonID ?
To assign Person entity to a Order without loading Person entity, you have to do something like this:
var db = new OneToManyEntities();
var Order = new Order { OrderId = 100, OrderName = "Order name" };
Order. PersonReference.EntityKey = new EntityKey("OneToManyEntities.Person ","PersonID",10);
db.AddToOrders(Order);
db.SaveChanges();
Puzzled's answer is correct for EF v1. It's a pain. If you don't mind the extra query, you can set the property succinctly:
int id = 1;
Order.Person = context.Persons.Where(x => x.PersonID == id).FirstOrDefault();
Entity Framework v4 will have "FK Associations", which is a fancy term for directly-settable foreign keys.