EFCore 3.0 Code First: Define Relations with Fluent API

Here is the summary of how EntityFrame Core 3.0 define entity relations with Fluent API.

1.  1-0:1

    1 student to 0:1 StudentAddress.

• Model classes:

    public class Student

    {

        public int Id { get; set; }

        public string LastName { get; set; }

        public string FirstMidName { get; set; }

        public StudentAddress Address { get; set; }

    }

    public class StudentAddress

    {

        public int StudentId { get; set; }

        public string AddressLine1 { get; set; }

        public string AddressLine2 { get; set; }

        public string City { get; set; }

        public string State { get; set; }

        public string Zip { get; set; }

        public Student Student { get; set; }

    }

• Mappings:

    public class StudentMap : IEntityTypeConfiguration<Student>

    {

        public void Configure(EntityTypeBuilder<Student> builder)

        {

            builder.ToTable(nameof(Student));

            builder.HasKey(x => x.Id);

        }

    }

    public class StudentAddressMap : IEntityTypeConfiguration<StudentAddress>

    {

        public void Configure(EntityTypeBuilder<StudentAddress> builder)

        {

            builder.ToTable(nameof(StudentAddress));

            builder.HasKey(u => u.StudentId);  // StudentAddress.StudentId is primary key

            builder.HasOne(u => u.Student)

                   .WithOne(b => b.Address)

                   .HasForeignKey<StudentAddress>(b => b.StudentId); // StudentAddress.StudentId is foreign key to Student.Id, too.

        }

    }

 public class SchoolContext : DbContext

    {

        public SchoolContext (DbContextOptions<SchoolContext> options)

            : base(options)

        {

        }

        public DbSet<Student> Students { get; set; }

        public DbSet<StudentAddress> StudentAddresses { get; set; }

     

        protected override void OnModelCreating(ModelBuilder modelBuilder)

        {

            modelBuilder.ApplyConfiguration(new StudentMap());

            modelBuilder.ApplyConfiguration(new StudentAddressMap());

        }

    }

• Generated tables:

CREATE TABLE [Student] (

    [Id] int NOT NULL IDENTITY,

    [LastName] nvarchar(max) NULL,

    [FirstMidName] nvarchar(max) NULL,

    CONSTRAINT [PK_Student] PRIMARY KEY ([Id])

);

CREATE TABLE [StudentAddress] (

    [StudentId] int NOT NULL,

    [AddressLine1] nvarchar(max) NULL,

    [AddressLine2] nvarchar(max) NULL,

    [City] nvarchar(max) NULL,

    [State] nvarchar(max) NULL,

    [Zip] nvarchar(max) NULL,

    CONSTRAINT [PK_StudentAddress] PRIMARY KEY ([StudentId]),

    CONSTRAINT [FK_StudentAddress_Student_StudentId] FOREIGN KEY ([StudentId]) REFERENCES [Student] ([Id]) ON DELETE CASCADE

);

2. 0:1-m

1. 1 Auther to 1:m Book.
2. 
   
3. public class SampleContext : DbContext
4. {
5. public DbSet<Book> Books { get; set; }
7. protected override void OnModelCreating(ModelBuilder modelBuilder)
8. {
9. modelBuilder.Entity<Author>()
10. .HasMany(a => a.Books)
11. .WithOne(b => b.Author);
12. }
13. }
14. 

16. public class Author
17. {
18. public int AuthorId { get; set; }
19. public string FirstName { get; set; }
20. public string LastName { get; set; }
21. public ICollection<Book> Books { get; set; }
22. }
23. 

25. public class Book
26. {
27. public int BookId { get; set; }
28. public string Title { get; set; }
29. public Author Author { get; set; }
30. }

3. 1-1:m

1. 1 Auther to 0:m Book.

Same as 1-0:m except IsRequired() is added in relation definition as below:

1. 
   
2. public class SampleContext : DbContext
3. {
4. public DbSet<Book> Books { get; set; }
6. protected override void OnModelCreating(ModelBuilder modelBuilder)
7. {
8. modelBuilder.Entity<Author>()
9. .HasMany(a => a.Books)
10. .WithOne(b => b.Author)
11. .IsRequired();
12. }
13. }
14.