9. EF Core and alternate key constraint index database

First, set the index

protected  the override  void OnModelCreating (the ModelBuilder modelBuilder) 
{ 
    modelBuilder.Entity <Blog> () .HasIndex (B => b.Url); // the Url field index 
    modelBuilder.Entity <Blog> () .HasIndex ( b => b.Url ) .IsUnique (); unique index // Url field 
    . modelBuilder.Entity <Blog> () HasIndex (b => b.Url) .HasName ( "Index_Url"); // set the index name Index_Url 
    modelBuilder.Entity < . blog> () HasIndex (b => b.Url) .HasFilter ( " filter"); // index data inside the composite HasFilter fill condition where conditions. All data HasFilter (null) indexing 
    modelBuilder.Entity <the Person> () .HasIndex (P => new new {p.FirstName, p.LastName}); // create a plurality of columns of an index

 }

 

Second, the alternate key: In addition to the primary key, alternate key can uniquely identify a data (with the same unique primary key constraint). Alternate key may be used as a target foreign key relationships. When using a relational database, the system will usually default when you need to introduce alternate key, you need to manually configure them, of course, you can manually configure

1, agreed to set: By convention, when the property that you identified as the primary key is not the target of the relationship, will be introducing you to spare key

class MyContext: the DbContext 
{ 
    public DbSet <Blog> Blogs { GET ; SET ;}
     public DbSet <Post> Posts { GET ; SET ;} 

    protected  the override  void OnModelCreating (the ModelBuilder modelBuilder) 
    { 
        modelBuilder.Entity <Post> () 
            .HasOne (P => p.Blog) 
            .WithMany (B => b.Posts) 
            .HasForeignKey (P => p.BlogUrl) 
            .HasPrincipalKey (B => b.Url); // no need to provide a spare key Url, EF Core will set up
    }
}

public class Blog
{
    public int BlogId { get; set; }
    public string Url { get; set; }

    public List<Post> Posts { get; set; }
}

public class Post
{
    public int PostId { get; set; }
    public string Title { get; set; }
    public string Content { get; set; }

    public string BlogUrl { get; set; }
    public Blog Blog { get; set; }
}

2, manual setting: Fluent API can be used to manually configure a single attribute alternate key

protected  the override  void OnModelCreating (the ModelBuilder modelBuilder) 
{ 
    modelBuilder.Entity <Car> () 
　　.HasAlternateKey (C => c.LicensePlate) // single attribute alternate key 
   .HasName ( "AlternateKey_LicensePlate"); // set alternate key name

    modelBuilder.Entity <Car> () .HasAlternateKey (C => new new {c.State, c.LicensePlate}); // set the composite alternate key
 
}

Note: By convention, the alternate key index and constraints is named AK_ <type name> _ <property name> format, the standby key combination <property name> is the name attribute partition list underscore