EF6具有导航属性的一对多fluent api

我正在尝试使用EF6和fluent API为我的实体应用一对多，但不断出现以下错误：

EmailTemplate_Attachments_Source_EmailTemplate_Attahments_Target:：关系约束中"从属角色"answers"主体角色"中的属性数必须相同。

这些是我的型号：

public class EmailTemplate
{
    public EmailTemplate()
    {
        Attachments = new List<EmailTemplateAttachment>();
    }
    public int EmailTemplateId { get; set; }
    public int OperatorId { get; set; }
    public EmailTemplateType MailType { get; set; }
    public int LanguageId { get; set; }
    public string Subject { get; set; }
    public string Content { get; set; }
    public string FromEmail { get; set; }
    public DateTime CreationDate { get; set; }
    public virtual ICollection<EmailTemplateAttachment> Attachments { get; set; }
}
public class EmailTemplateAttachment
{
    public int EmailTemplateAttachmentId { get; set; }
    public string ShortDescription { get; set; }
    public string FilePath { get; set; }
    public int EmailTemplateId { get; set; }
    public virtual EmailTemplate EmailTemplate { get; set; }
}

这些是实体配置

public EmailTemplateConfiguration()
    {
        ToTable("T_EMAILS");
        HasKey(emailTemplate => new { emailTemplate.OperatorId, emailTemplate.MailType, emailTemplate.LanguageId });
        HasMany(t => t.Attachments)
            .WithRequired(a => a.EmailTemplate)
            .HasForeignKey(a => a.EmailTemplateId);
        Property(emailTemplate => emailTemplate.EmailTemplateId).HasColumnName("row_id")
            .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
        Property(emailTemplate => emailTemplate.OperatorId).HasColumnName("operator_id");
        Property(emailTemplate => emailTemplate.MailType).HasColumnName("mail_type");
        Property(emailTemplate => emailTemplate.LanguageId).HasColumnName("language_id");
        Property(emailTemplate => emailTemplate.Subject).HasColumnName("subject");
        Property(emailTemplate => emailTemplate.Content).HasColumnName("mail_content");
        Property(emailTemplate => emailTemplate.FromEmail).HasColumnName("from_email");
        Property(emailTemplate => emailTemplate.CreationDate).HasColumnName("insert_date");
    }
 public EmailTemplateAttachmentConfiguration()
    {
        ToTable("T_EMAILS_ATTACHMENTS");
        HasKey(a => a.EmailTemplateAttachmentId);
        HasRequired(a => a.EmailTemplate)
            .WithMany(t => t.Attachments)
            .HasForeignKey(a => a.EmailTemplateId);
        Property(a => a.EmailTemplateAttachmentId).HasColumnName("attachment_id")
            .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
        Property(a => a.ShortDescription).HasColumnName("short_description");
        Property(a => a.FilePath).HasColumnName("file_url");
        Property(a => a.EmailTemplateId).HasColumnName("mail_id");
    }

我做错了什么？我已经尝试了很多次等待来配置外键，并一次又一次地获得相同的异常

HasKey(emailTemplate => new { emailTemplate.OperatorId, emailTemplate.MailType, emailTemplate.LanguageId });