EF 4 Code First - 我该如何建模？

Question

I am trying out EF and Code First approach

I have an Account model which looks like

public class Account
{
   public virtual int AccountID {get; set;}
   public virtual string AccountName {get; set;}
   public virtual Account ParentAccount {get; set;}
   public virtual Contact AccountOwner {get; set}
}

Contact class is a simple class

public class Contact
{
   public virtual int ContactID {get; set;}
   public virtual string ContactName {get; set;}
}

Now I have no idea how to add IDs to the account class.

Suppose I have set up the context correctly, what modifications are needed to the Account class so that

1. I can add an Account as the parent of another Account

2. I can access the ParentAccount of a particular Account

3. I can access the AccountOwner of a particular Account

I am new to this. Any help would be appreciated

Answer 1

Here's how I would solve this.

Add foreign key properties to your classes. I'm talking about ParentAccountId and AccountOwnerId . To make navigating things a bit easier, I have also added a collection of child accounts to Account and a collection of owned accounts to Contact. Note that it's not necessary to make "normal" properties virtual. Only navigational properties should be made virtual.

public class Account
{
    public int AccountID {get; set;}
    public string AccountName {get; set;}
    public int? ParentAccountId { get; set; }
    public int? AccountOwnerId { get; set; }

    public virtual Account ParentAccount { get; set; }
    public virtual ICollection<Account> ChildAccounts { get; set; }

    public virtual Contact AccountOwner { get; set; }

    public Account()
    {
        ChildAccounts = new List<Account>();
    }
}

public class Contact
{
    public int ContactID { get; set; }
    public string ContactName { get; set; }

    public virtual ICollection<Account> OwnedAccounts { get; set; }

    public Contact()
    {
        OwnedAccounts = new List<Account>();
    }
}

Next, create a mapping for the Account class to explain to EF how to setup the relationships.

public class AccountMapping : EntityTypeConfiguration<Account>
{
    public AccountMapping()
    {
        HasOptional(x => x.ParentAccount).WithMany(x => x.ChildAccounts).HasForeignKey(x => x.ParentAccountId);
        HasOptional(x => x.AccountOwner).WithMany(x => x.OwnedAccounts).HasForeignKey(x => x.AccountOwnerId);
    }
}

Finally, add the mapping to your DbContext class.

public MyContext : DbContext
{
    public DbSet<Account> Accounts { get; set; }
    public DbSet<Contact> Contacts { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Configurations.Add(new AccountMapping());
    }
}

Note that I have assumed that the AccountOwner and ParentAccount are optional. If they are required, simply change the type of the foreign properties from int? to int and change the HasOptional in the mappings to HasRequired .

Answer 2

public class Account
{
   [Key]
   public virtual int AccountID {get; set;}
   public virtual string AccountName {get; set;}
   public virtual Account ParentAccount {get; set;}
   public virtual Contact AccountOwner {get; set}
   public virtual IEnummerable<Account> ChiledAccount {get; set}
}

public class Contact
{
   [Key]
   public virtual int ContactID {get; set;}
   public virtual string ContactName {get; set;}
}

Answer 3

You can do this by without using Fluent API.That is by default conventions are maintained by EF.B'cos your mappings are simple.

You're having Account (1) : Contact (m) Relationship.

So try with below models

public class Account
{
   public int Id {get; set;}
   public string AccountName {get; set;}
      
   public virtual ICollection<Contact> AccountOwners { get; set; }
}


public class Contact
{
   public int Id {get; set;}
   public string ContactName {get; set;}

   public virtual Account ParentAccount {get; set;}
}

Then Your database tables will be created like below:

Accounts Table

Id            int             NotNull
AccountName   nvarchar(100)   AllowNull

   
Contacts Table

Id            int             NotNull
ContactName   nvarchar(100)   AllowNull
Account_Id    int             NotNull

If you need to do advance mappings then you have to learn Fluent API.