How to map a generic property to distinct columns of a table according to its type in EF Core?

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In EF Core, you can use the Table-per-Hierarchy (TPH) approach to map a generic property to distinct columns of a table according to its type. This approach allows you to create a single table that can store different types of entities with a discriminator column that will indicate the type of each entity.

To implement this approach, follow these steps:

1. Create a base class for your entities, which will contain the generic property that you want to map. For example:

public abstract class BaseClass
{
    public string GenericProperty { get; set; }
}

1. Create subclasses for each type of entity that you want to map to the table, and inherit from the base class. For each subclass, add a discriminator value that will indicate the type of the entity. For example:

public class EntityType1 : BaseClass
{
    public EntityType1()
    {
        Discriminator = "Entity1";
    }

    public string Property1 { get; set; }
    public string Property2 { get; set; }

    [NotMapped]
    public string Property3 { get; set; }

    [NotMapped]
    public int Property4 { get; set; }

    public string Discriminator { get; private set; }
}

public class EntityType2 : BaseClass
{
    public EntityType2()
    {
        Discriminator = "Entity2";
    }

    public string Property5 { get; set; }
    public string Property6 { get; set; }

    [NotMapped]
    public string Property7 { get; set; }

    [NotMapped]
    public int Property8 { get; set; }

    public string Discriminator { get; private set; }
}

Note that the discriminator value must be unique for each subclass.

1. Use the modelBuilder to configure the entity types and the table mapping. For example:

public class MyDbContext : DbContext
{
    public MyDbContext(DbContextOptions<MyDbContext> options) : base(options) {}

    public DbSet<BaseClass> MyEntities { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        // Add the discriminator value to each entity type
        modelBuilder.Entity<EntityType1>().HasDiscriminator<string>("discriminator")
            .HasValue<EntityType1>("Entity1");

        modelBuilder.Entity<EntityType2>().HasDiscriminator<string>("discriminator")
            .HasValue<EntityType2>("Entity2");

        // Map the entities to the table and their columns
        modelBuilder.Entity<BaseClass>().ToTable("MyTable")
            .HasDiscriminator<string>("discriminator")
            .WithMany()
            .HasForeignKey("discriminator");

        modelBuilder.Entity<EntityType1>()
            .Property(e => e.Property1).HasColumnName("Column1")
            .HasMaxLength(50);

        modelBuilder.Entity<EntityType1>()
            .Property(e => e.Property2).HasColumnName("Column2")
            .HasMaxLength(50);

        modelBuilder.Entity<EntityType2>()
            .Property(e => e.Property5).HasColumnName("Column3")
            .HasMaxLength(50);

        modelBuilder.Entity<EntityType2>()
            .Property(e => e.Property6).HasColumnName("Column4")
            .HasMaxLength(50);
    }
}

Note that in this example, the entities are mapped to a single table called "MyTable", and their columns are mapped according to their type. The discriminator column is also added to the table.

1. Insert entities of different types into the table using the DbSet. For example:

context.MyEntities.AddRange(
    new EntityType1 { GenericProperty = "Value1", Property1 = "Value2", Property2 = "Value3" },
    new EntityType2 { GenericProperty = "Value4", Property5 = "Value5", Property6 = "Value6" }
);

context.SaveChanges();

Now, the entities will be inserted into the table with their specific columns mapped according to their type, and EF Core will be able to retrieve them from the table and map them back to their respective objects.