Lets say I query the database and load a list of items. 开发者_如何学PythonThen 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

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.