How to define foreign key relationship in EF Core 2.1

问题

I am using EF Core 2.1 for my DAL. This is how my model looks like

One user can have only one role:

// Role entity - kind of master
public class Role
{
    public int RoleId { get; set; }

    public string RoleName { get; set; }
}

// User entity - every user will have one role
public class User
{
    public int UserId { get; set; }

    public string Email { get; set; }
    public string Password { get; set; }

    public int RoleId { get; set; }
    public bool IsActive { get; set; }
    public DateTime CreatedOn { get; set; }

    public virtual Role Role { get; set; }
}

This is how I was thinking/tried to define the relationship between these two entities:

public void Configure(EntityTypeBuilder<User> builder)
{
    builder.HasKey(x => x.UserId);
    builder.Property(x => x.RoleId).IsRequired(true);
    builder.Property(x => x.CreatedOn).IsRequired(true).HasDefaultValue(DateTime.Now);

    // FK - throwing compile time error 
    builder.HasOne(x => x.Role).WithOne(y => y.RoleId);
}

How do I define this one user one role relation using EF Fluent API?

Thanks.

Attachment:-

回答1:

Not only in the FK relationship configuration, you also have problem in the default value generation configuration for the CreatedOn column. So write your Entity Configuration as follows:

public void Configure(EntityTypeBuilder<User> builder)
{
    builder.HasKey(u => u.UserId);
    builder.Property(u => u.CreatedOn).IsRequired(true).HasDefaultValueSql("getdate()");

    // FK - configuraiton
    builder.HasOne(u => u.Role).WithMany().HasForeignKey(u => u.RoleId).IsRequired(true);
}

回答2:

One of the tenets Entity framework is built on is "Convention over configuration" and by convention, I don't think builder.HasOne(x => x.Role).WithOne(y => y.RoleId); is necessary as by convention you already stated that your User entity should have just one role when you added public int RoleId { get; set; } and public virtual Role Role { get; set; } properties. Remove that and I am certain your application will yield just that behaviour as stated in my comment above.

回答3:

I think you can add Users to Role like this

public class Role
{
    public int RoleId { get; set; }

    public string RoleName { get; set; }
    public List<User> Users {get;set;}
}

Then you will register like this

public void Configure(EntityTypeBuilder<User> builder)
{
    builder.HasKey(x => x.UserId);
    builder.Property(x => x.RoleId).IsRequired(true);
    builder.Property(x => x.CreatedOn).IsRequired(true).HasDefaultValue(DateTime.Now);


    builder.HasOne(x => x.Role).WithMany(y => y.Users);
}

来源：https://stackoverflow.com/questions/53681739/how-to-define-foreign-key-relationship-in-ef-core-2-1

标签

entity-framework

asp.net-core

ef-core-2.1