This is my first time exploring DataAnnotations (I was hoping to use this over fluent)...and I don't understand why the following code throws a compile time error:
CS0592 - Attribute 'Index' is not valid on this declaration type. It is only valid on 'class' declaration
public class Holiday
{
[Key]
public int Id { get; set; }
[Required]
[Index(IsUnique = true)]
public DateTime? Date { get; set; }
public string Name { get; set; }
}
My goal is to make the Date column UNIQUE...and I thought using [Index(IsUnique = true)] on a column is the correct way to make it unique...but it is not allowing me to use the Index attribute on columns, only on classes...
Please teach me how to achieve this? ๐๐๐
Well, the Index attribute is the data annotation equivalent of the HasIndex fluent API, and similar to the API, it's meant to be applied at the entity (class) level, providing the properties that make up the index, in order , plus other information such as the index. name, if it is unique, etc.
So in your case you would need something like this
[Index(nameof(Holiday.Date), IsUnique = true)] public class Holiday { // ... }which corresponds to the following fluent configuration
modelBuilder.Entity<Holiday>() .HasIndex(e => e.Date) .IsUnique();Actually all of this is well explained with examples in the Indexes section of the official EF Core documentation.