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Create reference data only when EF code first database is initially created

I have a table called "Invoice" and that has a field called "PaymentTypeId" which points to another table called "PaymentType".
Using EntityFramework code first, how do we add reference data such as:
PaymentTypeId: 1 | Description: Card
PaymentTypeId: 2 | Description: Cash
PaymentTypeId: 3 | Description: Cheque
But only when the database is first created?
I'm aware of the OnModelCreating override and I could select from the table to see if data exists, however; I see that as an extra Db call. Is there something else I can hook into to only insert reference data after inital creating of the database?
This is for an MVC5 application.
PS: Apologies if this has already been answered. Perhaps I'm searching the wrong terms.

You can override the seed method. In the Configuration.cs under Migrations folder:
protected override void Seed(YourDbContext context)
{
context.PaymentType.AddOrUpdate(x => x.Id,
new PaymentType() { Id = 1, Description= "Card" },
new PaymentType() { Id = 2, Description= "Cash" },
new PaymentType() { Id = 3, Description= "Cheque" }
);
}
Don't forget to add the required namespaces. You can see here for details.

EntityFramework update existing records with new foreign key

I have a database and a set of tables that already have data in.
I am using code first. Now I have been asked to add a Category table to the database and with that, to change some of the other tables to reference that table via a foreign key.
I know through previous experience, that if I update the database after changing the models, it will moan because an FK can't have 0.
So I want to use the Seed method to actually update the Foreign Keys as the database is updated.
I want to do something like this:
protected override void Seed(DatabaseContext context)
{
// Create our categories
context.Categories.AddOrUpdate(m => m.Id,
new Category { Id = 1, Name = "Cameras" },
new Category { Id = 2, Name = "Televisions" }
);
// Get all our current feeds
var feeds = context.Feeds.ToList();
context.Feeds.AddOrUpdate(m => m.Id, feeds.Select(m => m.CategoryId = 1).ToArray());
}
Can someone let me know how I might actually do this? Or if there is another way of doing it?

Inside a loop:
foreach(var f in context.Feeds)
{
f.CategoryId=1;
}
context.SaveChanges();
Or using Entity Framework Extended library to do it in one batch:
context.Feeds.Update(f=>new Feed{CategoryId=1});

Error in CodeFirst Seed with migrations : Modifying a column with the 'Identity' pattern is not supported. Column: 'CreatedAt'.

I have activated migrations on my Azure Mobile Services project. I filled the new seed function Inside the Configuration.cs class of the migrations. If the tables are empty, the seed function is going without any problems. When my AddorUpdate tries to update the first object I get the error in the inner exception : "Modifying a column with the 'Identity' pattern is not supported. Column: 'CreatedAt'. Table: 'CodeFirstDatabaseSchema.Category'."
Part of my code is as follows:
context.categories.AddOrUpdate(
new Category { Id="1", Code="GEN", Text="General"},
new Category { Id="2", Code="POL", Text="Politics"},
new Category { Id="3", Code="FAS", Text="Fashion"},
new Category { Id="4", Code="PEO", Text="People"},
new Category { Id="5", Code="TEC", Text="Technology"},
new Category { Id="6", Code="SPO", Text="Sport"},
new Category { Id="7", Code="LIV", Text="Living"}
);

Here's my generic implementation of Nikatlas' solution.
Short version of the answer: You can't modify CreatedAt with a null value, so you can use this function instead:
private void AddOrUpdatePreservingCreatedAt<T> (DbSet<T> set, T item) where T : EntityData
{
var existing = set.Where(i => i.Id == item.Id).FirstOrDefault();
if (existing != null)
{
item.CreatedAt = existing.CreatedAt;
}
set.AddOrUpdate(i => i.Id, item);
}
Call it like this
AddOrUpdatePreservingCreatedAt(context.YourItems, itemToBeUpdatedOrAdded);

It seems i have found a solution to this problem.
The reason this error occurs is because of the AddOrUpdate Method.
As stated in this post : http://thedatafarm.com/data-access/take-care-with-ef-4-3-addorupdate-method/
More importantly, if a match is found then the update will update all and null out any that weren’t in your AddOrUpdate.
What this means is that after the first seed, whenever your code runs it tries to update your entities correctly but it tries to pass the value null on CreatedAt field. If you look at EntityData class the CreateAt field has these attributes :
[DatabaseGenerated(DatabaseGeneratedOption.Identity)] //Here they mark this as IDENTITY
[Index(IsClustered = true)] // Cluster index. i really dont know why ?
[TableColumn(TableColumnType.CreatedAt)]
public DateTimeOffset? CreatedAt { get; set; }
So the error occurs beacause you try to modify the CreatedAt column.
My solution was to Create a List, lookup to set CreatedAt to correct value and then addOrUpdate:
// Create List
List<Permission> permissions = new List<Permission>(new Permission[]{
new Permission { Id = "ID1" , Name = "Send SMS"},
new Permission { Id = "ID2", Name = "Send Email"} });
// Iterate through list to set CreatedAt to correct value
foreach (Permission p in permissions){
// Get the record from the db if it exists
var t = context.PermissionSet.Where(s => s.Id == p.Id).FirstOrDefault();
if (t != null){
p.CreatedAt = t.CreatedAt; //SET CreatedAt to correct Value if the record already exists
}
context.PermissionSet.AddOrUpdate(a => a.Id, p); // NOW I CAN UPDATE WITH NO PROBLEM
}
Hope this helps. :)

If you have a integer column named Id, then Entity Framework will assume that is the primary key and that it is database generated - so it is created as an IDENTITY column in the database.
You cannot specify the Id for IDENTITY columns, so you stop doing that by removing the Id = 1, Id = 2, etc
I am a bit thrown by the fact that the column you have a problem with is named "CreatedAt". It sounds like it should be a DateTime and might also be database generated, but it surely shouldn't be IDENTITY?
Anyways, the usage you probably want is the one where you specify the natural key of the entity, so that EF can identify any records that already exist. So, if CODE is the natural key then you should be writing the Seed like this:
context.categories.AddOrUpdate(
x => x.Code,//the natural key is Code
new Category { Code="GEN", Text="General"},
new Category { Code="POL", Text="Politics"},
new Category { Code="FAS", Text="Fashion"},
new Category { Code="PEO", Text="People"},
new Category { Code="TEC", Text="Technology"},
new Category { Code="SPO", Text="Sport"},
new Category { Code="LIV", Text="Living"}
);
Reference:
Take care with the AddOrUpdate method

This question, its answers and comments might help you a bit, but not much.
You can do Inserts on identity column using the solutions provided by the question. But you cannot update values of Identity Column. The only way to do updates on identity column is to mark it as not being identity. Probably by adding manual migrations.
This SO question and its answers may also be helpful.
Read here also on general MSSQL Server constraints on Updating Identity Column.

SAME PROBLEM AND SOLUTION
We had the same problem and it was a trigger in another table that had impact on the table that we had the problem on.
DETAILS OF OUR DEVELOPMENT
We developed a Xamarin App connected to an Azure Web Service. When we used the method PushAsync from iMobileServices, it gave us the error: Modifying a column with the 'Identity' pattern is not supported. Column: 'CreatedAt'.
It was strange for us as some tables did not have the problem with the web service
REASON
It seems that the trigger update got in conflict with the pushasync from the mobile device.
We disabled the trigger, switched the responsibility to the front end and it worked fine. At least for us.
We hope this soltion helps someone.

How to add or remove a many-to-many relationship in Entity Framework?

There's a many-to-many UserFeed table that stands between User and Feed and denotes a twitter-like follow relationship.
It only has two fields, which form a composite key: UserID and FeedID.
I need to write a method that will subscribe or unsubscribe a user from a feed based on a boolean flag.
public void SetSubscriptionFlag (int userId, int storeId, bool subscribe)
{
}
I'm new to Entity Framework so I'm trying to find and follow an "EF-ish" way to accomplish this.
My initial thoughts are:
Instead of working with the middle UserFeed class, I should create a many-to-many Subscriptions property (EDIT: hit limitations here);
After I've done so, I'll need to fetch a User instance by ID, check whether it has given Feed in its Subscriptions and add/delete it depending on the flag and current existence;
Figure out how to avoid racing conflicts when there is a time interval before the check and adding/deleting and user manages to submit two adding or deletion requests;
Optimize my code as to avoid unneccessary SELECTs, if any occur, because all I really want to do is a single SELECT and single INSERT/DELETE.
A relevant code snippet and comment on my points is highly appreciated.
Thanks!

You can use dummy objects - it definitely works for insert and I hope it can be used for delete as well:
Create new relation:
var user = new User() { Id = userId };
context.Users.Attach(user);
var store = new Store() { Id = storeId };
context.Stores.Attach(store);
// Now context trackes both entities as "existing"
// and you can build a new relation
user.Subscriptions.Add(store);
context.SaveChanges();
Remove existing relation:
var user = new User() { Id = userId };
var store = new Store() { Id = storeId };
user.Subscriptions.Add(store);
context.Users.Attach(user);
// Now context trackes both entities as "existing"
// with "existing" relation so you can try to remove it
user.Subscriptions.Remove(store);
context.SaveChanges();

Update a record without first querying?

Lets say I query the database and load a list of items. Then I open one of the items in a detail view form, and instead of re-querying the item out of the database, I create an instance of the item from the datasource in the list.
Is there a way I can update the database record without fetching the record of the individual item?
Here is a sample how I am doing it now:
dataItem itemToUpdate = (from t in dataEntity.items
where t.id == id
select t).FirstOrDefault();
Then after pulling the record I update some values in the item and push the record back:
itemToUpdate.itemstatus = newStatus;
dataEntity.SaveChanges();
I would think there would be a better way to do this, any ideas?

You should use the Attach() method.
Attaching and Detaching Objects

You can also use direct SQL against the database using the context of the datastore. Example:
dataEntity.ExecuteStoreCommand
("UPDATE items SET itemstatus = 'some status' WHERE id = 123 ");
For performance reasons, you may want to pass in variables instead of a single hard coded SQL string. This will allow SQL Server to cache the query and reuse with parameters. Example:
dataEntity.ExecuteStoreCommand
("UPDATE items SET itemstatus = 'some status' WHERE id = {0}", new object[] { 123 });
UPDATE - for EF 6.0
dataEntity.Database.ExecuteSqlCommand
("UPDATE items SET itemstatus = 'some status' WHERE id = {0}", new object[] { 123 });

The code:
ExampleEntity exampleEntity = dbcontext.ExampleEntities.Attach(new ExampleEntity { Id = 1 });
exampleEntity.ExampleProperty = "abc";
dbcontext.Entry<ExampleEntity>(exampleEntity).Property(ee => ee.ExampleProperty).IsModified = true;
dbcontext.Configuration.ValidateOnSaveEnabled = false;
dbcontext.SaveChanges();
The result TSQL:
exec sp_executesql N'UPDATE [dbo].[ExampleEntities]
SET [ExampleProperty ] = #0
WHERE ([Id] = #1)
',N'#0 nvarchar(32),#1 bigint',#0='abc',#1=1
Note:
The "IsModified = true" line, is needed because when you create the new ExampleEntity object (only with the Id property populated) all the other properties has their default values (0, null, etc). If you want to update the DB with a "default value", the change will not be detected by entity framework, and then DB will not be updated.
In example:
exampleEntity.ExampleProperty = null;
will not work without the line "IsModified = true", because the property ExampleProperty, is already null when you created the empty ExampleEntity object, you needs to say to EF that this column must be updated, and this is the purpose of this line.

If the DataItem has fields EF will pre-validate (like non-nullable fields), we'll have to disable that validation for this context:
DataItem itemToUpdate = new DataItem { Id = id, Itemstatus = newStatus };
dataEntity.Entry(itemToUpdate).Property(x => x.Itemstatus).IsModified = true;
dataEntity.Configuration.ValidateOnSaveEnabled = false;
dataEntity.SaveChanges();
//dataEntity.Configuration.ValidateOnSaveEnabled = true;
Otherwise we can try satisfy the pre-validation and still only update the single column:
DataItem itemToUpdate = new DataItem
{
Id = id,
Itemstatus = newStatus,
NonNullableColumn = "this value is disregarded - the db original will remain"
};
dataEntity.Entry(itemToUpdate).Property(x => x.Itemstatus).IsModified = true;
dataEntity.SaveChanges();
Assuming dataEntity is a System.Data.Entity.DbContext
You can verify the query generated by adding this to the DbContext:
/*dataEntity.*/Database.Log = m => System.Diagnostics.Debug.Write(m);

Now native support for this in EF Core 7 — ExecuteUpdate:
Finally! After a long wait, EF Core 7.0 now has a natively supported way to run UPDATE (and also DELETE) statements while also allowing you to use arbitrary LINQ queries (.Where(u => ...)), without having to first retrieve the relevant entities from the database: The new built-in method called ExecuteUpdate — see "What's new in EF Core 7.0?".
ExecuteUpdate is precisely meant for these kinds of scenarios, it can operate on any IQueryable instance, and lets you update specific columns on any number of rows, while always issuing a single UPDATE statement behind the scenes, making it as efficient as possible.
Usage:
Imagine you wanted to update the Email column of a specific user:
dbContext.Users
.Where(u => u.Id == someId)
.ExecuteUpdate(b =>
b.SetProperty(u => u.Email, "NewEmail#gmail.com")
);
As you can see, calling ExecuteUpdate requires you to make calls to the SetProperty method, to specify which property to update, and also what new value to assign to it.
EF Core will translate this into the following UPDATE statement:
UPDATE [u]
SET [u].[Email] = "NewEmail#gmail.com"
FROM [Users] AS [u]
WHERE [u].[Id] = someId
Also, ExecuteDelete for deleting rows:
There's also a counterpart to ExecuteUpdate called ExecuteDelete, which, as the name implies, can be used to delete a single or multiple rows at once without having to first fetch them.
Usage:
// Delete all users that haven't been active in 2022:
dbContext.Users
.Where(u => u.LastActiveAt.Year < 2022)
.ExecuteDelete();
Similar to ExecuteUpdate, ExecuteDelete will generate DELETE SQL statements behind the scenes — in this case, the following one:
DELETE FROM [u]
FROM [Users] AS [u]
WHERE DATEPART(year, [u].[LastActiveAt]) < 2022
Other notes:
Keep in mind that both ExecuteUpdate and ExecuteDelete are "terminating", meaning that the update/delete operation will take place as soon as you call the method. You're not supposed to call dbContext.SaveChanges() afterwards.
If you're curious about the SetProperty method, and you're confused as to why ExectueUpdate doesn't instead receive a member initialization expression (e.g. .ExecuteUpdate(new User { Email = "..." }), then refer to this comment (and the surrounding ones) on the GitHub issue for this feature.
Furthermore, if you're curious about the rationale behind the naming, and why the prefix Execute was picked (there were also other candidates), refer to this comment, and the preceding (rather long) conversation.
Both methods also have async equivalents, named ExecuteUpdateAsync, and ExecuteDeleteAsync respectively.

I recommend using Entity Framework Plus
Updating using Entity Framework Core can be very slow if you need to update hundreds or thousands of entities with the same expression. Entities are first loaded in the context before being updated which is very bad for the performance and then, they are updated one by one which makes the update operation even worse.
EF+ Batch Update updates multiple rows using an expression in a single database roundtrip and without loading entities in the context.
// using Z.EntityFramework.Plus; // Don't forget to include this.
// UPDATE all users inactive for 2 years
var date = DateTime.Now.AddYears(-2);
ctx.Users.Where(x => x.LastLoginDate < date)
.Update(x => new User() { IsSoftDeleted = 1 });

Simple and elegant extension method:
I've written an extension method for DbContext that does exactly what the OP asked for.
In addition to that, it only requires you to provide a member initialization expression (e.g. new User { ... }), and it then figures out on its own what properties you've changed, so you won't have to specify them by hand:
public static void UpdateEntity<TEntity>(
this DbContext context,
int id,
Expression<Func<TEntity>> updateExpression
) where TEntity : BaseEntity, new()
{
if (updateExpression.Body is not MemberInitExpression memberInitExpr)
throw new ArgumentException("The update expression should be a member initialization.");
TEntity entityToUpdate = updateExpression.Compile().Invoke();
entityToUpdate.Id = id;
context.Attach(entityToUpdate);
var updatedPropNames = memberInitExpr.Bindings.Select(b => b.Member.Name);
foreach (string propName in updatedPropNames)
context.Entry(entityToUpdate).Property(propName).IsModified = true;
}
You also need a BaseEntity class or interface that has your primary key in it, like:
public abstract class BaseEntity
{
public int Id { get; set; }
}
Usage:
Here's how you'd use the method:
dbContext.UpdateEntity(1234 /* <- this is the ID */, () => new User
{
Name = "New Name",
Email = "TheNewEmail#gmail.con",
});
dbContext.SaveChanges();
Nice and simple! :D
And here's the resulting SQL that gets generated by Entity Framework:
UPDATE [Users]
SET [Name] = #p0, [Email] = #p1
WHERE [Id] = #p2;
Limitation:
This method only allows you to update a single row using its primary key.
So, it doesn't work with .Where(...), IQueryable<...>, and so on. If you don't have the PK, or you want to bulk-update, then this wouldn't be your best option. In general, if you have more complex update operations, then I'd recommend you use Entity Framework Plus, or similar libraries.

It works somewhat different in EF Core:
There may be a faster way to do this in EF Core, but the following ensures an UPDATE without having to do a SELECT (tested with EF Core 2 and JET on the .NET Framework 4.6.2):
Ensure your model does not have IsRequired properties
Then use the following template (in VB.NET):
Using dbContext = new MyContext()
Dim bewegung = dbContext.MyTable.Attach(New MyTable())
bewegung.Entity.myKey = someKey
bewegung.Entity.myOtherField = "1"
dbContext.Entry(bewegung.Entity).State = EntityState.Modified
dbContext.Update(bewegung.Entity)
Dim BewegungenDescription = (From tp In dbContext.Model.GetEntityTypes() Where tp.ClrType.Name = "MyTable" Select tp).First()
For Each p In (From prop In BewegungenDescription.GetProperties() Select prop)
Dim pp = dbContext.Entry(bewegung.Entity).Property(p.Name)
pp.IsModified = False
Next
dbContext.Entry(bewegung.Entity).Property(Function(row) row.myOtherField).IsModified = True
dbContext.SaveChanges()
End Using

ef core 7 :
public async Task<int> Update(UpdateLevelVm vm)
{
return await _db.Levels.Where(l => l.Id == vm.LevelId)
.ExecuteUpdateAsync(u => u
.SetProperty(l => l.GradeId, vm.GradeId)
.SetProperty(l => l.Title, vm.Title)
);
}

this has worked for me in EF core 3.1
await _unitOfWork.Context.Database.ExecuteSqlRawAsync("UPDATE Student SET Age = 22 Where StudentId = 123");

Generally speaking, if you used Entity Framework to query all the items, and you saved the entity object, you can update the individual items in the entity object and call SaveChanges() when you are finished. For example:
var items = dataEntity.Include("items").items;
// For each one you want to change:
items.First(item => item.id == theIdYouWant).itemstatus = newStatus;
// After all changes:
dataEntity.SaveChanges();
The retrieval of the one item you want should not generate a new query.