Complex Modeling

Motivation

Columns from database are flat, but sometimes we'll want to represent certain columns as a whole model to better describe them in code base. In other words, we need higher abstraction upon the columns.

Complex property

record class Person(string? FirstName, string? LastName);
public class Movie
{
    public int Identifier { get; set; }
    public string? Title { get; set; }
    public DateTime ReleaseDate { get; set; }
    public string? Synopsis { get; set; }
    public string? DirectorFirstName { get; set; } // [!code --]
    public string? DirectorLastName { get; set; } // [!code --]
    public Person? Director { get; set; } // [!code ++]
}

Entity framework core will spread properties of Director as column mappings for database, which means we should have Director_FirstName and Director_LastName as columns in database.

builder.ComplexProperty(movie => movie.Director); // spread the structured property

Certainly, we can override mappings if you don't like the convetion.

builder.ComplexProperty(movie => movie.Director)
    .Property(movie => movie.FirstName) // [!code highlight]
    .HasColumnName("d_firstname"); // [!code highlight]

Complex modeling across tables

// equivalent to `ComplexProperty`
builder.OwnsOne(movie => movie.Director); // each movie entity owns one director

Generally we should separate the columns about something obviously not primitive to the table itself into another table for preventing pollution.

builder.OwnsOne(movie => movie.Director)
    .ToTable("Directors") // move director to another table

Since director is owned by Movie entity, Entity framework core generates a foreign key in director table as reference for movie table(also a primary key). But director table is not independent, if a row of movie is removed, the director row will also be removed(yes directors are not reused).

INFO

It's not common solution we do in database design, it's just a showcase.

OwnsMany

One movie will have multiple casts.

public class Movie
{
    public int Identifier { get; set; }
    public string? Title { get; set; }
    public DateTime ReleaseDate { get; set; }
    public string? Synopsis { get; set; }
    public Person? Director { get; set; }
    public ICollection<Person>? Casts { get; set; } // [!code ++]
}

While one entity can own many other entites, we use OwnsMany.

builder.OwnsMany(movie => movie.Casts)
    .ToTable("Casts"); // [!code highlight]