I created an MVC 4 application using EF (Code First) which mapped to a mixture of tables and views which I created using SQL Management Studio which worked fine.
I have started a new MVC 4 project in much the same way as the first, using a completely different database, but this time anytime I try to use a model which maps to a view (not a table), an exception is raised saying that "An object with the name xxx already exists". The SQL profiler shows that EF is trying to create a table for my model.
I find that if I drop the views, let EF create the tables from the models, then delete the tables and replace them with view manually, the application will work for about 2 minutes, reading and using the information from my view, but eventually throwing the same exception.
I have no idea what is going on here.
The code that causes the exception is:
repository.Customers.OrderBy(c => c.AccountNumber);
where the model is:
public class Customer
{
public int Id {get;set;}
public string AccountNumber {get;set;}
public string Name {get;set;}
}
OK - the possible cause of this issue is hiding in your context file. There is probably a statement similar to the one below that is trying to update your database when the model changes.
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
Database.SetInitializer<MyContext>(new DropCreateDatabaseIfModelChanges<MyContext>());
}
I generally don't use this method. I prefer to delete the database and re-generate it using the package manager console. (Check out the update-database method of the package manager console)
Using Greg's hint I was able to arrive at the point where I simply added:
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
Database.SetInitializer<MyContext>(null);
}
to the context class and this has solved the issue. My understanding here is that I have told EF to do no initialisation, essentially having it map to an existing database that is maintained outside of the code first context.
I have voted up Greg's response as it was the help I needed but creating a new answer as it was the above that solved it eventually. I hope this was done right.
Related
My program has an existing SQLite database.
In the new version of the program, it needs to add a column for a feature.
Now the program is made by .NET 6 (WPF) and EF Core 6.
I have to detect whether the new column existed and add it or not.
Here is my code in OnModelCreating to detect the column existed or not:
protected override void OnModelCreating(ModelBuilder builder)
{
base.OnModelCreating(builder);
var Result = Database.ExecuteSqlRaw("SELECT Count(*) FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME='BindDesign' AND COLUMN_NAME='type'");
}
After the code run, it reports this error:
An attempt was made to use the model while it was being created. A DbContext instance cannot be used inside 'OnModelCreating' in any way that makes use of the model that is being created
How can I solve this? Thank you.
You should use migrations to add columns in the database.
If you want to apply migrations on startup you can check if the database needs to be migrated and apply the migration with something like this
if (_context.Database.GetPendingMigrations().Any()) {
await _context.Database.MigrateAsync();
}
Try to Use Different Context for your schema , the error message is clear , you can on use makes use of the model that is being created.
just make another context for your schema .
I have a class named "Ciudad". When I want to add a migration to create the datatable, EF uses the name "dbo.Ciudads". I actually wanted the name to be "Ciudades" (with an additional 'e') so I changed it manually.
After updating the databse the table dbo.Ciudades was created successfully. I even created a small script to populate it and it run ok.
However, when I want to query "Ciudades" from the context, I get an exception because it tries to query the table "dbo.Ciudads" (without the additional 'e') which doesn't actually exists. It is an InvalidOperationException: "The model backing the 'ApplicationDbContext' context has changed since the database was created"
So I ran "add-migration foo" and it generates the following migration:
public partial class foo : DbMigration
{
public override void Up()
{
RenameTable(name: "dbo.Ciudads", newName: "Ciudades");
}
public override void Down()
{
RenameTable(name: "dbo.Ciudades", newName: "Ciudads");
}
}
It seems strange because in my database I DO have the table exactly as I wanted with the name "Ciudades". Nevertheless, when I try to update the database with this migration, I get the following exception:
System.Data.SqlClient.SqlException (0x80131904): Either the parameter #objname is ambiguous or the claimed #objtype (OBJECT) is wrong.
I imagine I get this exception because the table "Ciudads" doesn't exist. Am I correct?
If so, where it is getting that table from? I did a search on the Entire Solution for the word "ciudads" and nothing came up.
Thanks to #IvanStoev for the solution.
The problem was that I manually changed the table name in the generated migration class. Later I used FluentAPI to specify the name "Ciudades" but it was to late.
As per #IvanStoev suggestion I deleted everything and created the migrations again, but this time using FluentAPI BEFORE creating the migrations. The table was then generated with the name I intended and everything is working fine now.
You can use this approach .
public override void Up()
{
RenameTable("dbo.Ciudads", "Ciudades");
}
public override void Down()
{
RenameTable("dbo.Ciudades", "Ciudads");
}
Or
If you want to specify your table name.You can use fluent API.
modelBuilder.Entity<Department>().ToTable("t_Department");
It's probably worth downloading microsoft SQL server management studio dev edition.
Im unable to scaffold a controller (MVC5 Controller with views, using Entity Framework) in Visual studio 2013 (update 3 and 4). The error message is below:
There was an error running the selected code generator:
A configuration for type 'Library.Morthwind.Models.Catgeory' has already been added. To reference the existing configuration use the Entity<T>() or ComplexType<T>() methods
I have created the models by selecting 'Reverse Engineer Code First' from the 'Entity Framework Power Tools Beta 4' Tool menu.
Any ideas about what might cause this error?
I had the same issue today.
I had added some custom configuration for one of my Model classes to add a relationship using the fluent API. This was specified in my dbContext class in the OnModelCreating override using the following:
modelBuilder.Configurations.Add(new OrderConfiguration());
Commenting out the above line allowed the Controller scaffolding to run as expected.
VS 2013 update 2 had a problem with this and the scaffolding came up with an unhelpful error with no further information. In installed Update 3 and it gave just enough detail to track down the underlying issue.
Jeff.
I've been having this issue too. Jeff's solution works in some cases. But as my DbContext grew with more models that had keys needing to be mapped I couldn't delete the Configurations.Add() methods because I would then get errors that EF couldn't find primary keys, etc...
I did discover that by changing my DBContext derived class to use IDbSet properties instead of DbSet I could generate the controllers and views just fine. However, for me this introduced another issue, IDbSet does not support the async methods.
It appears I can either generate non-async controllers with configurations in place or async methods without configuration classes.
If your context properties are of type DbSet, try changing them to IDbSet. If you aren't generating async controller methods this may work for you.
I also had the same issue and changing my context class to use IDbSet allowed me to successfully use the scaffolding to create a new controller. But since I didn't want to give up the async methods I changed the context back to use DbSet and that worked for me.
Here is how I resolved this issue.
I have Visual Studio 2013 Update 4.
I use EF Power Tools.
Comment out all of the DbSet < ... >
Inside OnModelCreating, only leave the object you are scaffolding:
modelBuilder.Configurations.Add(new SomeTableDataMap());
At the bottom of my context class I did notice this got created:
public System.Data.Entity.DbSet SomeTableDatas{ get; set; }
Oh: I also put this in my constructor but it's for something else,
this.Configuration.LazyLoadingEnabled = false;
Seriously, this worked today, I've tried all of these solutions nothing worked for Update 4. I had this working in Update 2 and Update 3 using previous solutions. This is the most up-to-date solution for now.
Simple workaround that worked for me (after trying many other solutions suggested here and other places in vain...).
In the scaffolding dialog I just added a new DataContext e.g. TempContext. All the scaffolding worked as expected and then I could simply move the generated code in TempContext into my original DbContext and renamed the TempContext in the generated controllers to the original DbContext.
There are already multiple workarounds posted for this issue. And in this comment, I will try to provide the underlying issue why this may be failing. [With the hope to make people aware of the root cause]
Let's say, you have a DbContext (to be specific, child class of DbContext) in your application, and you are trying to use a model class (let's say Model) and the DbContext and scaffolding controllers / views.
I am guessing that the DbContext did not have a "DbSet< Model > Models {get; set;}" property on it but the DbSet was nevertheless added to the DbContext using code in OnModelCreating method.
In the above case, scaffolding first tries to detect DbSet property on DbContext (by reflection only - so that does not detect if OnModelCreating has code to add the DbSet) and given it's not, scaffolding adds a DbSet property to the DbContext and then tries to scaffold using that DbContext , however when running the scaffolding, we create an instance of DbContext and we also call OnModelCreating , and at that point, scaffolding fails because there are multiple DbSet types with the same model in the DbContext (one added by scaffolding and one configured in code in OnModelCreating).
[This happens not only for the model being used but also for related models in that model , scaffolding adds DbSet properties for all related models]
[Also, one doesn't see the added DbSet's after the scaffolding is done because scaffolding rolls back any changes if the operation did not complete successfully, like Jeff mentioned , the error message was poor initially and was improved to give some hint to the user but it's still not super clear what's going on]
This is a bug in scaffolding , a simple work around would be to use DbSet property on DbContext for all related models of your model class instead of configuring them in OnModelCreating.
I was getting a different error when trying to scaffold a controller with CRUD actions and views. In my case it was saying:
"There was an error running the selected code generator. Object instance
not set to an instance of the object."
The problem was hard to find: I created a table in SQL Server but forgot to set the Primary Key for the table. Setting the Primary key and updating Entity Framework's .edmx file solved the problem.
Hope it helps.
None of the rest of the answers worked for me. What I found out was that the issue only happened when scaffolding and adding Configurations using the Fluent API. So what I did was, instead of having separated files, each one having an Entity Configuration like this:
public class ApplicationUserMapConfiguration : EntityTypeConfiguration<ApplicationUserMap>
{
public ApplicationUserMapConfiguration()
{
ToTable("ApplicationUserMap", "Users");
HasKey(c => c.Id);
}
}
And then adding this configuration to the DbContext:
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Configurations.Add(new ApplicationUserMapConfiguration());
}
I just added the whole configuration inside the DbContext for every entity:
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
//ApplicationUser
modelBuilder.Entity<ApplicationUser>().HasKey(c => c.Id);
modelBuilder.Entity<ApplicationUser>().ToTable("ApplicationUser", "Usuario");
//Other entities...
}
Now I can scaffold perfectly. I already submited and issue on the Mvc GitHub.
Also, if another error message raises up saying:
There was an error running the selected code generator: ‘Exception has been thrown by the target of an invocation.’
You should modify your DbContext constructor to:
public YourDbContext() : base("YourDbContext", throwIfV1Schema: false) { }
None of answers of this post worked for me. I handled this issue creating new context class through plus button in Add Controller scaffolding dialog. Once VS created controller and views, I just remove the created context class and change the the generated controller code to use my existing context class.
Important: This process will add a new connection string for the new context, dont forget to remove it as well.
mine got fixed like this:
public virtual DbSet<Category> Categories { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
//--> EntityTypeConfiguration<Your Model Configuration>
modelBuilder.Configurations.Add(new EntityTypeConfiguration<CategoryMapping>());
base.OnModelCreating(modelBuilder);
}
DOn't forget Ctrl + Shift + B so your code compile (i'm not sure for single solution, but since mine is in another project in same solution, it should get compiled first)
I solved it by adding a try/catch on the code to OnModelCreating function inside the context class.
Just keep the
base.OnModelCreating(modelBuilder);
outside your try/catch
I have a local database that is currently in it's second version and should now go to it's third version.
The code for the previous migrations was generated by another programmer so I am assuming I am doing something wrong here.
In my model there are around 30 classes, and inside the model folder there is a mapping folder and it contains the mappings for those 30 classes.
So now I added 1 new class in the same manner as those previous classes and then run the add-migration command in the Package Manager Console.
Infortunately I get an empty migration Up() and Down() method.
When I look in the database there is a __migrationHistory available with the previous 2 migrations. If I run my application now, the third migration is also added but obviously the new table is not being created because it's not in the Up() method.
What could I be doing wrong?
I think something is going wrong when scaffolding the previous migrations... It's like it can't find the new Code-First classes I have added.
This is my command:
add-migration "1.2" -verbose -ProjectName "MyEFproject"
I am assuming that the scaffolding doesn't know where to look for the new class... or is this by convention that all model classes are just expected to be in the project?
Result of add-migration:
namespace MyProject.Migrations
{
using System;
using System.Data.Entity.Migrations;
public partial class _1002 : DbMigration
{
public override void Up()
{
}
public override void Down()
{
}
}
}
Sample of new Model Class:
using System;
using System.Collections.Generic;
namespace MyProject.Models
{
public partial class MyTable
{
public string SomeId { get; set; }
public string SomeText { get; set; }
}
}
Sample of new Mapping class
using System.ComponentModel.DataAnnotations.Schema;
using System.Data.Entity.ModelConfiguration;
namespace MyProject.Models.Mapping
{
public class MyTableMap : EntityTypeConfiguration<MyTable>
{
public MyTableMap()
{
// Primary Key
this.HasKey(t => t.SomeId);
// Properties
this.Property(t => t.SomeText)
.IsRequired()
.HasMaxLength(30);
// Table & Column Mappings
this.ToTable("MyTable", "database");
this.Property(t => t.SomeId).HasColumnName("SomeId");
this.Property(t => t.SomeText).HasColumnName("SomeText");
}
}
}
Thank you,
You need to add your table to your implementation of the DbContext class, e.g.
public class MyDatabaseEntities : DbContext {
public virtual DbSet<MyTable> MyTable { get; set; }
}
While rolling back an existing EF Core Data Context back to empty, my migrations wouldn't generate until I removed the ApplicationDbContextModelSnapshot that accompanied the migrations.
This class is auto-generated and needs to align with your current migration level.
I was able to fix this issue by deleting a record of last migration from _MigrationHistory table.
This record had been incorrectly created before I added DbSet for new model object to DbContext class.
After this deletion new migration was created with correct Up() and Down() methods.
I had this problem because I forgot to add {get; set;} after my variable names
You need to add your table to your implementation of the DbContext class, e.g. While rolling back an existing EF Core Data Context back to empty, my migrations wouldn't generate until I REMOVED the ApplicationDbContextModelSnapshot that accompanied the migrations.
In my case, the datacontext project is a class lib project. It is different from the startup project which is asp.net mvc 5 project. Now by mistake the connection string in the startup project is pointing to a different database.
So ensure that datacontext project and startup project point to the same database. Also use the full command as mentioned in the question like the following. You can include -Force as well.
add-migration "InitialMigration" -verbose -ProjectName "MyEFproject" -Force
Also: Make sure any new properties you've added are public!
In my case I was doing a migration where I added fields to an existing table and was ending up with empty Up and Down methods,
I had something like this:
public bool ExistingField { get; set; }
bool NewField { get;set; }
Can you spot the difference...?
If you make this mistake rerun the migration with the same name (you probably will need to add the -Force parameter to scaffold it full).
PS. Always make sure your project builds fully before attempting to do any kind of EF command. If your project doesn't already build you're asking for trouble.
You need to add your MyTable in Dbset and your issue will be resolved:
public DbSet<MyTable> MyTables { get; set; }
I was getting empty migrations added when I had mistakenly related two tables using a 1-many relationship rather than a many-many (i.e. i forgot one of the navigation properties). I had a seeding file that was expecting a many-many relationship and was subsequently failing during the migration causing the migration to fail. Unfortunately there was no output that made it obvious that was the problem and it was only by using the Entity Framework Power Tools (v4 but installed in VS2015) did i visually see the incorrect relationship and realize it was probably the cause.
I had to Update-Database with the latest migration before the empty one appending this parameter -TargetMigration:"{your-migration-name}".
Probably it will tell you that there will be data loss from the next buggy one we tried. If you can afford it append -Force to it.
Then I tried to add my new Add-Migration and it wasn't empty.
Final thing that you may need to do if above is throwing exception is to go SQL Server Management Studio and delete the last Automatic migration and try to add it again.
if new tables added to Context
just remove new table in "Migration/ExampleContextModelSnapshot"
I had the same issue on EFcore. When renaming Phone -> mobile, the migration came up empty.
My DbContext :
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<MyUser>()
.Property(c => c.Mobile)
.HasColumnName("phone");
}
Problem was using .HasColumnName("phone") was overriding the actual property name so EF probably couldn't see any change.
Changing string value made it work.
I had this exact issue after I wanted to add an extra column to my database. Because my data would not seed unless the tables were empty, I deleted all the tables and the migrations to recreate the tables. When I tried to migrate, the migration had empty up and down methods.
I solved this by deleting the snapshot file as this was creating the issue. So I deleted all the migrations and the snapshot file, added the migration again and ran update database. The tables and migrations were successfully updated with my new column.
A better way to do this though is to run the down method and drop the tables like that if you are working on test data. Obviously this is bad in the real world to drop tables.
To me the problem was that Id property that should correspond to table id was named FeedbackId.
I changed to "Id" and then Up/Down weren't empty anymore.
Dunno if that can help somehow
If your project is small, i.e. you do not have too many migrations yet, you can delete all from your Migration folder. After that, add the migrations again.
I think this also happens when u try to do migration without any changes in the models. eg when you do migration one and succeed, when u try to do migration2 without doing any changes in any of the models, it will create empty UP and Down.
From the perspective of a complete Entity Framework (Core) beginner:
Create your class which will become your table
You can have subclasses with many-to-many or one-to-one relationships.
In step 3 you see the context where both properties have a one-to-one relationship.
Ensure you have one DbContext
If you have more than one DbContext you need to specify which context you want to add the migration to with the -Context parameter.
Add your class to your DbContext as shown by #CondingIntrigue
As a reference The Entity Framework Core DbSet
public class AccountContext : DbContext
{
public DbSet<Account> Accounts { get; set; }
public DbSet<SecretIdentity> SecretIdentity { get; set; }
}
Enter Add-Migration
In my case, I was encountering similar problems with Visual Studio Code.
I have fixed these by doing the following:
Check inside your ContextModelSnapshot : ModelSnapshot
Comment Model Entity Definition…
Delete your migration files related to these entity
Delete the migrations from the dbo.__EFMigrationsHistory table
Compile your solution.
Run the following commands:
dotnet ef migrations add migrationName -p ProjectContainer/
dotnet watch run
Temprorary remove
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
}
and then do initial create
Add-Migration InitialCreate
If after adding your class in the dbContext and your migration is still empty: do the following:
In your DbContextModelSnapshot class, remove every related code to that class name that you are trying to apply add-migration on. Save the DbContextModelSnapshot.cs and use the Add-Migration "Added_filename"
This work for me.
In my case ,I deleted Migration folder completely. As long as I didn't remove the "ApplicationDbContextModelSnapshot" and all previous migrationas it didn't work.
For me it was because I hadn't add Configuration files.
onModelCreating:
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
modelBuilder.ApplyConfigurationsFromAssembly(typeof(AppDbContext).Assembly);
}
and add configurations in same assembly derived from IEntityTypeConfiguration<T> where T is your model.
I missed adding
{get;set}
After adding getter and setter, up and down methods are not empty.
My code is giving me an EntityCommandExecutionException when i'm trying getting data from my Bieren Table.
The exception message says that it can't find "dbo.Biers" which is quite obvious because it's called "dbo.Bieren".
I can quite easily fix this by just renaming the table in the database. Altough i don't like fixing my database around my code's errors.
How can i make the entity framework use the correct table instead of changing the name of my table?
Thanks in advance.
Decorate your entity class with the TableAttribute property, e.g.
[Table("Bieren")]
For the database-first approach, StriplingWarrior's solution works well. But if you use the code-first approach, you could use System.ComponentModel.DataAnnotations.TableAttribute on a target entity class to map an entity class to a database table.
However, this way is slightly annoying, because we commonly want to define a pure entity class. To do this, you could entrust it to another class or use the overrided OnModelCreating method in the DbContext class as the following.
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<Category>()
.ToTable("MyCategories");
}
Your Entity Framework model has information about the table names and connections that it is connecting to. If you're using a database-first approach, you should have an EDMX file with your database model in it. The easiest way is to update the model from the database.
Open the EDMX file in Visual Studio
Delete the incorrect "Biers" table
right-click in the background and click "Update Model from database"
Point the wizard at your database, and select the "Bieren" table to add
Finish the wizard, and the "Bieren" table should appear
It is also possible to dig into the properties of the Biers type, and manually change the table name.