Entity Framework mappings to relational Relation Mapping (Entity Framework multi-to-Multi-link ing), entitymapping

Entity Framework mappings to relational Relation Mapping (Entity Framework multi-to-Multi-link ing), entitymapping

Generally, when we design a database, there will be two tables with many-to-many relationships. When the database has many-to-many relationships, we usually process them through intermediate join tables, so how do we deal with it in EF?

Assume that we have the following relationship: A User contains multiple roles. When a Role contains multiple users, how can we use EF to deal with such a database design?

Next, let's take a look at the following code list:

First, let's look at our User and Role entities.

 1 public class User 2  3 { 4  5     public User() {} 6  7   8  9     public int UserId { get; set; }10 11     public string Name { get; set; }12 13     public string Password { get; set; }14 15     public string PasswordSalt { get; set; }16 17     public Byte Status { get; set; }18 19     public DateTime CreatedDate { get; set; }20 21     public DateTime ModifiedDate { get; set; }22 23 }24 25 public class Role26 27 {28 29      public Role() {}30 31      public int RoleId { get; set; }32 33      public string RoleName { get; set; }34 35 }

Next, we know that a User contains multiple roles, so add such code to the User object.

public virtual ICollection<Role> Roles { get; set; }

 

Add this code to the User constructor.

this.Roles = new HashSet<Role>();

 

Similarly, a Role also contains multiple users, so add such code to the Role object

public virtual ICollection<User> Users { get; set; }

 

Add this code to the Role constructor.

this.Users = new HashSet<User>();

 

Next, construct the DataContext class inherited from the DbContext class.

public class DataContext : DbContext{    public DataContext()        : base("DataContext")    {    }    public DbSet<User> Users { get; set; }    public DbSet<Role> Roles { get; set; }    protected override void OnModelCreating(DbModelBuilder modelBuilder)    {            }}

 

Then, we generate our project and we can see the database relationships we have generated.

We can see that the link table in the middle generates User_UserId and Role_RoleId, but we may not define this in actual work or want to customize it more. Next we use the Fluent API (note: the literal translation here is a smooth API declaration. You can understand it literally, but I am not sure about it) to declare data. The link here isA user can contain multiple roles. A role can also contain multiple users.In the OnModelCreating method of DataContext, write as follows:

modelBuilder.Entity<User>()    .HasMany(r => r.Roles).WithMany(u => u.Users);

 

Further, we specify the intermediate chain table

 modelBuilder.Entity<User>()     .HasMany(r => r.Roles)     .WithMany(u => u.Users)     .Map(ur =>     {         ur.MapLeftKey("UserId");         ur.MapRightKey("RoleId");         ur.ToTable("UserRoles");     });

 

References:

Http://www.cnblogs.com/panchunting/p/entity-framework-code-first-fluent-api-configuring-relationships.html