Entity Framework Core add unique constraint code-first

Question

I can\'t find way to add a unique constraint to my field with using attribute:

public class User
{
    [Required]
    public int Id { get; set; }

    [Requi         


        

Answer 1

Also if you want to create Unique constrains on multiple columns you can simply do this (following @Sampath's link)

class MyContext : DbContext
{
    public DbSet<Person> People { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Person>()
            .HasIndex(p => new { p.FirstName, p.LastName })
            .IsUnique(true);
    }
}

public class Person
{
    public int PersonId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

Answer 2

We can add Unique key index by using fluent api. Below code worked for me

protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {

        modelBuilder.Entity<User>().Property(p => p.Email).HasColumnAnnotation("Index", new IndexAnnotation(new IndexAttribute("IX_EmailIndex") { IsUnique = true }));

    }

Answer 3

None of these methods worked for me in .NET Core 2.2 but I was able to adapt some code I had for defining a different primary key to work for this purpose.

In the instance below I want to ensure the OutletRef field is unique:

public class ApplicationDbContext : IdentityDbContext
    {
        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            base.OnModelCreating(modelBuilder);
            modelBuilder.Entity<Outlet>()
                .HasIndex(o => new { o.OutletRef });
        }
    }

This adds the required unique index in the database. What it doesn't do though is provide the ability to specify a custom error message.

Answer 4

Solution for EF Core

public class User
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Passport { get; set; }
}

public class ApplicationContext : DbContext
{
    public DbSet<User> Users { get; set; }
    public ApplicationContext()
    {
        Database.EnsureCreated();
    }
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer(@"Server=(localdb)\mssqllocaldb;Database=efbasicsappdb;Trusted_Connection=True;");
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<User>().HasAlternateKey(u => u.Passport);
        //or: modelBuilder.Entity<User>().HasAlternateKey(u => new { u.Passport, u.Name})
    }
}

DB table will look like this:

CREATE TABLE [dbo].[Users] (
    [Id]       INT            IDENTITY (1, 1) NOT NULL,
    [Name]     NVARCHAR (MAX) NULL,
    [Passport] NVARCHAR (450) NOT NULL,
    CONSTRAINT [PK_Users] PRIMARY KEY CLUSTERED ([Id] ASC),
    CONSTRAINT [AK_Users_Passport] UNIQUE NONCLUSTERED ([Passport] ASC)
);

Ref to EF Core docs

Answer 5

On EF core you cannot create Indexes using data annotations.But you can do it using the Fluent API.

Like this inside your {Db}Context.cs:

protected override void OnModelCreating(ModelBuilder builder)
{
    builder.Entity<User>()
        .HasIndex(u => u.Email)
        .IsUnique();
}

...or if you're using the overload with the buildAction:

protected override void OnModelCreating(ModelBuilder builder)
{
    builder.Entity<User>(entity => {
        entity.HasIndex(e => e.Email).IsUnique();
    });
}

You can read more about it here : Indexes

Answer 6

Ef core support unique configuration.

protected override void OnModelCreating(ModelBuilder builder)
{
  builder.Entity<Account>()
    .HasIndex(account => account.Email)
      .IsUnique();
}

Ef core support multiple unique keys

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
  modelBuilder.Entity<Account>()
      .HasKey(account => new { account.Id, account.Email, account.RoleId });
}

Don't forget run ef core command to make migration and update the database

>> dotnet ef migrations add MigrationName -c YourDbContextName
>> dotnet ef database update -c YourDbContextName