Update a record without first querying?

Question

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);

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 = "[email protected]",
});
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.