Here is an example of how to model a one-to-many relation with Entity Framework using database first.

UseCase: One user can write multiple Blogs, but a Blog is written by one user. This results in a one-to-many relationship between user and blog.

What I like to model looks like this:

one-to-many relation between user and blog

one-to-many relation between user and blog

We need to model two tables: User and Blog.

User.sql

CREATE TABLE [dbo].[User] (
    [Id]   INT            IDENTITY (1, 1) NOT NULL,
    [Name] NVARCHAR (MAX) NULL,
    CONSTRAINT [PK_dbo.User] PRIMARY KEY CLUSTERED ([Id] ASC)
);

Blog.sql

CREATE TABLE [dbo].[Blog] (
    [Id]      INT            IDENTITY (1, 1) NOT NULL,
    [Name]    NVARCHAR (MAX) NULL,
    [User_Id] INT            NULL,
    CONSTRAINT [PK_dbo.Blog] PRIMARY KEY CLUSTERED ([Id] ASC),
    CONSTRAINT [FK_dbo.Blog_dbo.User_User_Id] FOREIGN KEY ([User_Id]) REFERENCES [dbo].[User] ([Id])
);
GO
CREATE NONCLUSTERED INDEX [IX_User_Id]
    ON [dbo].[Blog]([User_Id] ASC);

The entities belonging to this model look like this:

User.cs

public partial class User
{
    public User()
    {
        this.Blogs = new HashSet<Blog>();
    }
    
    public int Id { get; set; }
    public string Name { get; set; }
    
    public virtual ICollection<Blog> Blogs { get; set; }
}

Blog.cs

public partial class Blog
{
    public int Id { get; set; }
    public string Name { get; set; }
    public Nullable<int> User_Id { get; set; }
    
    public virtual User User { get; set; }
}

Further Reading: