In EF Core you could use the extension method HasAlternateKey
in fluent API only. There are no data annotations to realize a unique constraint.
This MS doc article - Alternate Keys (Unique Constraints) - will explain how to use and which further possibilities are exist.
A short example from link above:
class MyContext : DbContext
{
public DbSet<Car> Cars { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Car>()
.HasAlternateKey(c => c.LicensePlate)
.HasName("AlternateKey_LicensePlate");
}
}
class Car
{
public int CarId { get; set; }
public string LicensePlate { get; set; }
public string Make { get; set; }
public string Model { get; set; }
}
Also it's possible to define an unique index. Therefore, in EF Core you can use the fluent API's extension method HasIndex
or the data annotation way with the attribute [Index]
.
In this MS doc article - Indexes - you will find further information how to use.
Here an example for an unique index with fluent API:
class MyContext : DbContext
{
public DbSet<Blog> Blogs { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Blog>()
.HasIndex(b => b.Url)
.IsUnique();
}
}
public class Blog
{
public int BlogId { get; set; }
public string Url { get; set; }
}
Here the same example, but with data annotation:
[Index(nameof(Url), IsUnique = true)]
public class Blog
{
public int BlogId { get; set; }
public string Url { get; set; }
}
Update 2021-09-10
- added additional info how to use with data annotation, because it's now available in EF Core;
Update 2021-09-24
- fixed missing IsUnique property in attribute example
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