EF5 Code First (Error cannot be inferred from the usage)

问题

Ok, I have been pulling out my hair because I simply cannot make a many to many relationship. I have the following two models:

public class UserProfile
{
    [Key]
    [DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
    public int UserId { get; set; }
    public string UserName { get; set; }
    public string CompanyName { get; set; }
    public string FirstName { get; set; }
    public string Lastname { get; set; }
    public string EmailAddress { get; set; }
    public string PhoneNumber { get; set; }
    public bool? ChangePassword { get; set; }
    public bool? Deletable { get; set; }

    //Add more Properties for more fields

    public virtual IQueryable<CompanyInformation> ParentCompany { get; set; }
}

and

public class CompanyInformation
{
    [Key]
    [DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
    public int id { get; set; }

    [DisplayName("Company Name:")]
    public string companyName { get; set; }

    [DisplayName("Website Address:")]
    [Url(ErrorMessage="The Website field is not a valid fully-qualified http, https, or ftp URL. (Example: http://www.website.com)")]
    public string website { get; set; }
    public string contactTitle { get; set; }

    [DisplayName("Contact First Name:")]
    public string contactFirstName { get; set; }
    //[Required]
    [DisplayName("Contact Last Name:")]
    public string contactLastName { get; set; }

    [Phone]
    [DisplayName("Phone Number:")]
    public string contactPhoneNumber { get; set; }

    [DisplayName("Address Display?")]
    public bool displayAddress { get; set; }
    [DisplayName("Phone Number?")]
    public bool displayPhoneNumber { get; set; }

    [DisplayName("Address 1:")]
    public string address1 { get; set; } 
    [DisplayName("Address 2:")]
    public string address2 { get; set; }

    [DisplayName("City:")]
    public string city { get; set; }

    [DisplayName("State:")]
    public string state { get; set; }

    [DisplayName("Zip/Postal Code:")]
    public string zipCode { get; set; }

    [DisplayName("Search Engine?")]
    public bool allowSearchEngines { get; set; }


    //Navigation Property
    public virtual IQueryable<UserProfile> CompanyUsers{ get; set; }

}

I'm trying to make a many-to-many relationship between these two and I just can't figure out how to do it properly. I should mention that I am very new to the EF Code First. My Context Class looks like the following:

public class myDB : DbContext
{
    public SchedulerDB()
        : base("DefaultConnection")
    {

    }

    public DbSet<UserProfile> UserProfiles { get; set; }
    public DbSet<CompanyInformation> Companies { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<UserProfile>().HasMany(e => e.ParentCompanies).WithMany(e => e.CompanyUsers);            
    }

}

ok, As soon as I add the modelBuilder above I get the following error:

The type arguments for method 'System.Data.Entity.ModelConfiguration.EntityTypeConfiguration<Scheduler.Model.UserProfile>.HasMany<TTargetEntity>(System.Linq.Expressions.Expression<System.Func<Scheduler.Model.UserProfile,System.Collections.Generic.ICollection<TTargetEntity>>>)' cannot be inferred from the usage. Try specifying the type arguments explicitly.  C:\Users\Hiva\Documents\Project\ToDo\Infrastructure\myDB.cs

What am I doing wrong? I can't seem to find any examples that use the modelBuilder differently to achieve a many-to-many relationship between two tables. Thank you in advanced for your help.

回答1:

You should use ICollection for navigation properties:

ICollection<UserProfile> CompanyUsers{ get; set; }

and

ICollection<UserProfile> ParentCompanies{ get; set; }

instead of IQueriable

来源：https://stackoverflow.com/questions/14351690/ef5-code-first-error-cannot-be-inferred-from-the-usage