多对多:无法确定由导航属性表示的关系。

Question

我试图使用代码优先工作流添加迁移，但是EF核心似乎不承认我的"TeamMember“和"Step”类之间的多到多关系。

我的“踏步”课：

public class Step {
    public int Id { get; set; }
    public int ProjectId { get; set; }
    public Project Project { get; set; }

    [Required]
    [StringLength(30, MinimumLength = 3, ErrorMessage = "The step name must have between 3 and 30 characters!")]
    public string Name { get; set; }

    [Required]
    [StringLength(500, MinimumLength = 10, ErrorMessage = "The step description must have between 10 and 500 characters!")]
    public string Description { get; set; }

    public ICollection<TeamMember> TeamMembers{ get; set; }        

    public Step() {
    }
}

我的TeamMember课：

public class TeamMember {
    public int Id { get; set; }
    public int UserId{ get; set; }
    public User User{ get; set; }
    public string Role { get; set; }
    public int TeamId { get; set; }
    public Team Team{ get; set; }

    public ICollection<Step> Steps{ get; set; }

    public TeamMember() {            
    }
}   

我的文脉课：

public class ProjectContext : IdentityDbContext<User> {
    public ProjectContext(DbContextOptions<ProjectContext> options)
       : base(options) {
    }

    public DbSet<User> User { get; set; }
    public DbSet<Project> Projects { get; set; }
    public DbSet<Team> Teams { get; set; }
    public DbSet<Step> Steps { get; set; }        
    public DbSet<TeamMember> TeamMembers{ get; set; }
    protected override void OnModelCreating(ModelBuilder builder) {
        builder.Entity<User>().HasKey(m => m.Id);
        builder.Entity<Project>().HasKey(m => m.Id);
        builder.Entity<Team>().HasKey(m => m.Id);
        builder.Entity<Step>().HasKey(m => m.Id);
        builder.Entity<TeamMember>().HasKey(m => m.Id);
        base.OnModelCreating(builder);
    }
}

错误字符串:无法确定导航属性'Step.TeamMembers‘所表示的关系。或者手动配置关系，或者使用“NotMapped”属性忽略此属性，或者在“OnModelCreating”中使用“EntityTypeBuilder.Ignore”。

正如您所看到的，我在每个类中都有一个ICollection，我无法判断错误。

Answer 1

默认情况下，EF不支持多到多的关系。

为了实现这种关系，您必须创建一个连接表：

您可以这样轻松地配置它：

步骤：

public class Step {
    public ICollection<TeamMemberStep> TeamMemberStep { get; set; }        
}

小组成员：

public class TeamMember {
    public ICollection<TeamMemberStep> TeamMemberStep { get; set; }
}

连接表：

public class TeamMemberStep
{
    public string TeamMemberId { get; set; }
    public virtual TeamMember TeamMember { get; set; }
    public int StepId { get; set; }
    public virtual Step Step { get; set; }
}

DbContext：

modelBuilder.Entity<TeamMemberStep>()
    .HasKey(aup => new { aup.TeamMemberId, aup.StepId });

public DbSet<TeamMemberStep> TeamMemberSteps { get; set; }

现在，您将查询TeamMemberStep表以从任何一方获取数据。