How to update only one field using Entity Framework?

Here's the table

Users

UserId
UserName
Password
EmailAddress

and the code..

public void ChangePassword(int userId, string password){
//code to update the password..
}

Ladislav's answer updated to use DbContext (introduced in EF 4.1):

public void ChangePassword(int userId, string password)
{
    var user = new User() { Id = userId, Password = password };
    using (var db = new MyEfContextName())
    {
        db.Users.Attach(user);
        db.Entry(user).Property(x => x.Password).IsModified = true;
        db.SaveChanges();
    }
}

You can tell EF which properties have to be updated in this way:

public void ChangePassword(int userId, string password)
{
  var user = new User { Id = userId, Password = password };
  using (var context = new ObjectContext(ConnectionString))
  {
    var users = context.CreateObjectSet<User>();
    users.Attach(user);
    context.ObjectStateManager.GetObjectStateEntry(user)
      .SetModifiedProperty("Password");
    context.SaveChanges();
  }
}

In Entity Framework Core, Attach returns the entry, so all you need is:

var user = new User { Id = userId, Password = password };
db.Users.Attach(user).Property(x => x.Password).IsModified = true;
db.SaveChanges();

You have basically two options:

• go the EF way all the way, in that case, you would
  • load the object based on the userId provided - the entire object gets loaded
  • update the password field
  • save the object back using the context's .SaveChanges() method

In this case, it's up to EF how to handle this in detail. I just tested this, and in the case I only change a single field of an object, what EF creates is pretty much what you'd create manually, too - something like:

`UPDATE dbo.Users SET Password = @Password WHERE UserId = @UserId`

So EF is smart enough to figure out what columns have indeed changed, and it will create a T-SQL statement to handle just those updates that are in fact necessary.

• you define a stored procedure that does exactly what you need, in T-SQL code (just update the Password column for the given UserId and nothing else - basically executes UPDATE dbo.Users SET Password = @Password WHERE UserId = @UserId) and you create a function import for that stored procedure in your EF model and you call this function instead of doing the steps outlined above

i'm using this:

entity:

public class Thing 
{
    [Key]
    public int Id { get; set; }
    public string Info { get; set; }
    public string OtherStuff { get; set; }
}

dbcontext:

public class MyDataContext : DbContext
{
    public DbSet<Thing > Things { get; set; }
}

accessor code:

MyDataContext ctx = new MyDataContext();

// FIRST create a blank object
Thing thing = ctx.Things.Create();

// SECOND set the ID
thing.Id = id;

// THIRD attach the thing (id is not marked as modified)
db.Things.Attach(thing); 

// FOURTH set the fields you want updated.
thing.OtherStuff = "only want this field updated.";

// FIFTH save that thing
db.SaveChanges();