EF Core HasMany

The Entity Framework Core Fluent API HasMany method is used to configure the many side of a one-to-many relationship. The HasMany method must be used in conjunction with the HasOne method to fully configure a valid relationship, adhering to the Has/With pattern for relationship configuration.

The following model represents companies and employees with an inverse navigation property defined in the dependent entity (Employee):

public class Company
{
    public int Id { get; set; }
    public string Name { get; set; }
    public ICollection<Employee> Employees { get; set; }
}

public class Employee
{
    public int Id { get; set; }
    public string Name { get; set; }
    public Company Company { get; set; }
}

A company has many employees, each with one company. That relationship is represented as follows:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Company>()
        .HasMany(c => c.Employees)
        .WithOne(e => e.Company);
}

Data Annotations

Relationships can be defined with the ForeignKey and InverseProperty attributes.

Further Reading

• Relationships
• Configuring One To Many Relationships
• Configuring One To One Relationships