MVC implementation of many to many relationships - asp.net-mvc

Question

This is done using MVC .net framework and entity framework "database first" approach. There is a many to many relationship between two tables. They are connected through third table that has combined key as id from first table and id from second table.
public class ManyToManyTable
{
[Required]
[Key, Column(Order=0)]
public int firsttableid { get; set; }
[Required]
[Key, Column(Order=1)]
public int secondtableid { get; set; }
public int something { get; set; }
[ForeignKey("firsttableid")]
public virtual FirstTable firstTable { get; set; }
[ForeignKey("secondtableid")]
public virtual SecondTable secondTable { get; set; }
}
First and Second table have some id which is primary key.
I want to create View and Controller method that enables master detail entry form for this ManyToManyTable. that would have FirstTable in Master and SecondTAble in details, and all to be saved in ManyToManyTable when button Save is pressed.
Of course, both First and Second Table have this property:
public virtual ICollection<ManyToManyTable> ManyToManyTables { get; set; }
What is the easiest way to implement cases like this one?
Thank you!

Answer 1

EF has a default conventions for many-to-many relationships. No need to create specific
mapping class. You have to include navigation properties in both "FirstTable" and "SecondTable" Class as shown below.
public class FirstTable
{
public FirstTable()
{
secondTableProperties = new HashSet<SecondTable>();
}
public int Id { get; set; }
public int MyProperty2 { get; set; }
public int MyProperty3 { get; set; }
public virtual ICollection<SecondTable> secondTableProperties { get; set; }
}
public class SecondTable
{
public SecondTable()
{
FirstTableProperties = new HashSet<FirstTable>();
}
public int Id { get; set; }
public int MyProperty2 { get; set; }
public int MyProperty3 { get; set; }
public virtual ICollection<FirstTable> FirstTableProperties { get; set; }
}
Remove mapping class from DBContext , only include above two classes. Build and run the application , EF will automatically create a Mapping table in SQL server. Usually the Mapping table contains only the primary keys of other two tables.
You can use Fluent API to take some control on the created mapping table
modelBuilder.Entity<FirstTable>()
.HasMany<SecondTable>(s => s.FirstTableProperties)
.WithMany(c => c.secondTableProperties)
.Map(cs =>
{
cs.MapLeftKey("FirstTableId");
cs.MapRightKey("SecondTableId");
cs.ToTable("ManyToManyTable");
});
If you want to work with a join table with additional properties, above mentioned many-to-many relationship won't work . In that case you will have to create two one-to-many relationships as shown below.
public class FirstTable
{
public int Id { get; set; }
public int MyProperty2 { get; set; }
public virtual ICollection<ManyToManyTable> manytomany { get; set; }
}
public class SecondTable
{
public int Id { get; set; }
public int MyProperty2 { get; set; }
public virtual ICollection<ManyToManyTable> manytomany { get; set; }
}
public ManyToManyTable
{
[Required]
[Key, Column(Order=0)]
public int firsttableid { get; set; }
[Required]
[Key, Column(Order=1)]
public int secondtableid { get; set; }
public int AdditionalProperty { get; set; }
public virtual FirstTable first { get; set; }
public virtual SecondTable Second { get; set; }
}