EntityFramework添加到多对多

Question

I have a Vacation and a list of Countries. I whish to bind these together using a many-to-many relationship. I have a code-first Vacations model and Countries model. Both the individual tables aswell as the join table are successfully generated.

However, when I try to add a country to a vacation (or vice versa) the join table remains empty. I am able to successfully add the individual vacations aswell as the countries.

Models

public class Vacations
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int VacationId { get; set; }

    public string ProductId { get; set; }

    public string Name { get; set; }

    public string Price { get; set; }

    public virtual ICollection<Countries> Countries { get; set; }


    public Vacations()
    {
        Countries = new List<Countries>();
    }
}



public class Countries
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int CountryID { get; set; }
    public string CountryName { get; set; }

    public virtual ICollection<Vacations> Vacations { get; set; }
    public Countries()
    {
        Vacations = new List<Vacations>();
    }
}




public class MyContext : DbContext
{
    public MyContext()
        : base("myconn")
    {
    }

    public DbSet<Vacations> Vacations { get; set; }

    public DbSet<Countries> Countries { get; set; }
}

Insert the Vacation

            Vacations vacation = database.Vacations.Add(new Vacations
            {
                Name = vacationData.Name,
                Description = vacationData.Description,
            });

            database.SaveChanges();            
            // to make sure the key is in the database to refrence

            foreach (string country in AllMyCountries)
            {
                Countries countries = database.Countries.Add(new Countries
                {
                    CountryName = country
                });
                countries.Vacations.Add(vacation);
                vacation.Countries.Add(countries);
            }

            database.SaveChanges();

I have also tried just adding to one entity, and adding more calls to SaveChanges() inbetween.

Answer 1

Interesting problem in that your sample code all looks perfectly okay. Infact, I put a quick test together around this code and Entity Framework created the mapping table vacationscountries as expected and populated it correctly.

Just on the off-change, can you confirm that you are looking in the mapping table created by Entity Framework and not a custom mapping table? The only reason I mention it is that theres no way (that I know of) to map a many-to-many relationship to a custom junction table using Data Annotations.

If thats not the case, then the next thing I would do is to trace out the sql being generated by Entity Framework - either using your native database tracing tooling (eg Sql Profiler), a third party tool like EFProf, or through a logging interceptor ( http://msdn.microsoft.com/en-gb/data/dn469464.aspx ). Hopefully that will give some lower-level insights into the problem.

Answer 2

I re-created your Models but made some adjustments that generate the same results. I manually created the junction table VacationsCountries with the following code:

public class VacationsCountries
{
    [Key, Column(Order = 0)]
    public int VacationId { get; set; }
    public virtual Vacations Vacation { get; set; }
    [Key, Column(Order = 1)]
    public int CountryId { get; set; }
    public virtual Countries Country { get; set; }
}

I also added this line of code to the MyContext class:

public DbSet<VacationsCountries> VacationsCountries { get; set; }

Instead of using:

countries.Vacations.Add(vacation);
vacation.Countries.Add(countries);

I use:

VacationsCountries vc = database.VacationsCountries.Add(new VacationsCountries
{
    Country = countries,
    Vacation = vacation
});

and then call database.SaveChanges();

I checked the database and the entries were added to the VacationsCountries table.