EF7单向多对多配置报错：所有跳过导航必须配置外键

配置EF Core多对多关系时，Workflow类的Contatori属性触发以下错误：

OneTimeSetUp: System.InvalidOperationException : The skip navigation 'Contatore.Workflow1' doesn't have a foreign key associated with it. Every skip navigation must have a configured foreign key.

相关代码及Oracle表结构如下：

实体类代码 #

public class Workflow
{
    public required int Id { get;  set; }
    public virtual ICollection<Contatore> Contatori { get; set; } = new HashSet<Contatore>();
}

public class Contatore
{
    public override int Id { get; set; }

    public virtual ICollection<Contatore> ContatoriFigli { get; set; } = new HashSet<Contatore>();
    public virtual ICollection<Contatore> ContatoriPadri { get; set; } = new HashSet<Contatore>();
}

配置类代码 #

internal class ContatoreConfiguration : IEntityTypeConfiguration<Contatore>
{
    public void Configure(EntityTypeBuilder<Contatore> builder)
    {
        builder
            .ToTable($"NAT_{Costanti.CodiceApplicazione}_CONTATORE_003")
            .HasKey(c => c.Id)
            .HasName("NAK_DASH_003");

        builder.Property(b => b.Id)
            .HasColumnName("ID_003")
            .HasComment("Chiave primaria")
            .HasDefaultValueSql($"SYUNA{Costanti.CodiceApplicazione}.SEQ_{Costanti.CodiceApplicazione}_003.NEXTVAL");
        
        builder.HasMany(x => x.ContatoriFigli)
            .WithMany(x => x.ContatoriPadri)
            .UsingEntity("NAT_DASH_CONTATORE_LINKS_004",
                m => m.HasOne(typeof(Contatore)).WithMany().HasForeignKey("IdContatorePrincipale").HasPrincipalKey(nameof(Contatore.Id)),
                s => s.HasOne(typeof(Contatore)).WithMany().HasForeignKey("IdContatoreCollegato").HasPrincipalKey(nameof(Contatore.Id)),
                j => {
                    j.Property("IdContatorePrincipale").HasColumnName("ID_CONT_PRINC_004");
                    j.Property("IdContatoreCollegato").HasColumnName("ID_CONT_COLL_004");
                    j.HasKey("IdContatorePrincipale", "IdContatoreCollegato");
                }
            );
    }
}

internal class WorkflowConfiguration : IEntityTypeConfiguration<Workflow>
{
    public void Configure(EntityTypeBuilder<Workflow> builder)
    {
        builder
            .ToTable($"NAT_DASH_WORKFLOW_005")
            .HasKey(c => c.Id)
            .HasName("NAK_DASH_005");

        builder.Property(b => b.Id)
            .HasColumnName("ID_005")
            .HasComment("Chiave primaria")
            .HasDefaultValueSql($"SYUNA{Costanti.CodiceApplicazione}.SEQ_{Costanti.CodiceApplicazione}_005.NEXTVAL");
               
        builder.HasMany(x => x.Contatori)
            .WithMany()
            .UsingEntity("NAT_DASH_WORKFLOW_CONTATORE_006",
                m => m.HasOne(typeof(Workflow)).WithMany().HasForeignKey("ID_WORKFLOW_006").HasPrincipalKey(nameof(Workflow.Id)),
                s => s.HasOne(typeof(Contatore)).WithMany().HasForeignKey("ID_CONTATORE_006").HasPrincipalKey(nameof(Contatore.Id))
            );
    }
}

Oracle中间表结构 #

CREATE TABLE "NAT_DASH_WORKFLOW_CONTATORE_006"
   (    
    "ID_WORKFLOW_006" NUMBER (9,0),
    "ID_CONTATORE_006" NUMBER (9,0), 
    CONSTRAINT NAF_DASH_006_004 FOREIGN KEY (ID_WORKFLOW_006) REFERENCES NAT_DASH_WORKFLOW_005 (ID_005),
    CONSTRAINT NAF_DASH_006_005 FOREIGN KEY (ID_CONTATORE_006) REFERENCES NAT_DASH_CONTATORE_003 (ID_003)
    );

问题根源：使用.WithMany()不带参数时，EF Core会为Contatore自动生成隐式导航属性（如Workflow1），但配置未为该隐式导航关联有效外键，导致报错。以下两种方案可解决：

方案1：添加显式反向导航并配置 #

1. 修改Contatore类，添加反向导航属性：

public class Contatore
{
    public override int Id { get; set; }

    public virtual ICollection<Contatore> ContatoriFigli { get; set; } = new HashSet<Contatore>();
    public virtual ICollection<Contatore> ContatoriPadri { get; set; } = new HashSet<Contatore>();
    // 新增反向导航
    public virtual ICollection<Workflow> Workflows { get; set; } = new HashSet<Workflow>();
}

2. 更新WorkflowConfiguration中的多对多配置，指定反向导航：

builder.HasMany(x => x.Contatori)
    .WithMany(x => x.Workflows) // 指定反向导航属性
    .UsingEntity("NAT_DASH_WORKFLOW_CONTATORE_006",
        m => m.HasOne(typeof(Workflow)).WithMany().HasForeignKey("ID_WORKFLOW_006").HasPrincipalKey(nameof(Workflow.Id)),
        s => s.HasOne(typeof(Contatore)).WithMany().HasForeignKey("ID_CONTATORE_006").HasPrincipalKey(nameof(Contatore.Id))
    );

方案2：完整配置中间表映射（不添加反向属性） #

若不想新增反向导航，需在UsingEntity中完整定义中间表的键和外键映射：

builder.HasMany(x => x.Contatori)
    .WithMany()
    .UsingEntity("NAT_DASH_WORKFLOW_CONTATORE_006",
        right => right.HasOne(typeof(Contatore)).WithMany().HasForeignKey("ID_CONTATORE_006"),
        left => left.HasOne(typeof(Workflow)).WithMany().HasForeignKey("ID_WORKFLOW_006"),
        join => join
            .Property("ID_WORKFLOW_006").HasColumnName("ID_WORKFLOW_006")
            .Property("ID_CONTATORE_006").HasColumnName("ID_CONTATORE_006")
            .HasKey("ID_WORKFLOW_006", "ID_CONTATORE_006")
    );

内容的提问来源于stack exchange，提问作者gt.guybrush