[Entity Framework 6] Code First (5) - Relations

 Entity Framework   Code first    Relations  

▌Introduction

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How to design code-first models for these relations

1.  One-to-one

2.  One-to-many

3.  Many-to-many

▌Environment

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▋Entity Framework 6.2.0

▌Implement

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Let’s see the final result as following,

Suppliers(供應商) 1 <-> 1 SupplierInCharges(供應商負責人)

Suppliers(供應商) 1 <-> 0..* Factorys(工廠)

Suppliers(供應商) * <-> * Customers(客戶)

▋1.Data Annotation Attribute

Gist

▋One-to-one

[Table("Suppliers")]

public class Supplier

{

        [Key]

        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]

        public int Id { get; set; }

        #region One-to-one

        public virtual SupplierInCharge InCharge { get; set; }

        #endregion

}

[Table("SupplierInCharges")]

public class SupplierInCharge

{

        [Key]

        [DatabaseGenerated(DatabaseGeneratedOption.None)]

        [ForeignKey("Supplier")]

        public int Id { get; set; }

        #region One-to-one

        public virtual Supplier Supplier { get; set; }

        #endregion

}

Notice that both the values of the primary keys in Suppliers and SupplierInCharges will be the same when inserting an object:Supplier.

▋One-to-many

[Table("Suppliers")]

public class Supplier

{

        [Key]

        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]

        public int Id { get; set; }

        #region One-to-many

        public virtual ICollection<Factory> Factorys { get; set; }

        #endregion

}

[Table("Factorys")]

public class Factory

{

        [Key]

        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]

        public int Id { get; set; }

        [Required]

        public int SupplierId { get; set; }

        #region Many-to-one

        [ForeignKey("SupplierId")]

        public virtual Supplier Supplier { get; set; }

        #endregion

}

▋Many-to-many

[Table("Suppliers")]

public class Supplier

{

        [Key]

        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]

        public int Id { get; set; }

        #region Many-to-many

        public virtual ICollection<Customer> Customers { get; set; }

        #endregion

}

[Table("Customers")]

public class Customer

{

        [Key]

        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]

        public int Id { get; set; }

        #region Many-to-many

        public virtual ICollection<Supplier> Suppliers { get; set; }

        #endregion

}

▋2.Fluent API

Gist

We will replace Data Annotation with Fluent API, so first we remove all data annotations on the models.

▋Models

[Table("Suppliers")]

public class Supplier

{

        [Key]

        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]

        public int Id { get; set; }

        #region One-to-one

        public virtual SupplierInCharge InCharge { get; set; }

        #endregion

        #region One-to-many

        public virtual ICollection<Factory> Factorys { get; set; }

        #endregion

        #region Many-to-many

        public virtual ICollection<Customer> Customers { get; set; }

        #endregion

}

[Table("SupplierInCharges")]

public class SupplierInCharge

{

        [Key]

        [DatabaseGenerated(DatabaseGeneratedOption.None)]

        public int Id { get; set; }

        #region One-to-one

        public virtual Supplier Supplier { get; set; }

        #endregion

}

[Table("Factorys")]

public class Factory

{

        [Key]

        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]

        public int Id { get; set; }

        [Required]

        public int SupplierId { get; set; }

        #region Many-to-one

        public virtual Supplier Supplier { get; set; }

        #endregion

}

[Table("Customers")]

public class Customer

{

        [Key]

        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]

        public int Id { get; set; }

        [StringLength(100)]

        public string Name { get; set; }

        [StringLength(200)]

        public string Address { get; set; }

        #region Many-to-many

        public virtual ICollection<Supplier> Suppliers { get; set; }

        #endregion

}

▋DbContext

public class AppDbContext : System.Data.Entity.DbContext

    {

        public AppDbContext()

            : base("name=AppDbContext")

        {

        }

        public DbSet<Supplier> Suppliers { get; set; }

        public DbSet<Factory> Factorys { get; set; }

        public DbSet<SupplierInCharge> SupplierInCharges { get; set; }

        public DbSet<Customer> Customers { get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)

        {

            #region Relations

            //One-to-one

            modelBuilder.Entity<Supplier>().HasRequired(m => m.InCharge).WithRequiredPrincipal(m => m.Supplier);

            //One-to-many

            modelBuilder.Entity<Supplier>().HasMany(m => m.Factorys).WithRequired(m => m.Supplier);

            //Many-to-many

            modelBuilder.Entity<Supplier>()

                .HasMany<Customer>(s => s.Customers)

                .WithMany(c => c.Suppliers)

                .Map(cs =>

                {

                    cs.MapLeftKey("SupplierId");

                    cs.MapRightKey("CustomerId");

                    cs.ToTable("SupplierCustomers");

                });

            #endregion

            #region Cascade setting

            modelBuilder.Entity<Supplier>().HasRequired(i => i.InCharge)

                .WithRequiredPrincipal(i => i.Supplier).WillCascadeOnDelete(true);

            #endregion

        }

}

Notice that we specified the column name on SupplierCustomers, so the final table will be like this,

▌Reference

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▋Configure One-to-Zero-or-One Relationship in Entity Framework 6

▋Configure Many-to-Many Relationships in Code-First