MVC4保存数据使用多对多关系 [英] MVC4 save data using Many to Many relationship

问题描述

许多关系

protected override void OnModelCreating(DbModelBuilder modelBuilder) 
{
modelBuilder.Entity<Company>()
    .HasMany(c => c.Tags)
    .WithMany(t => t.Companies)
    .Map(m =>
    {
        m.MapLeftKey("Companyid");
        m.MapRightKey("tagid");
        m.ToTable("CompanyTags");
    }
}

添加公司

var company = new Company() { Name = "FooBar Inc" };

添加标签

int tagId = _db.Tags.Where(x => x.Title == tag).Select(x => x.Id).SingleOrDefault();
if (tagId==0)
   company.Add(new Tag { Title = tag});
else
    ?????? //still create a relationship in CompanyTags (companyid,tagid)


context.Companies.Add(company);
context.SaveChanges();

如何配置一个新的com pany被创建，并且标签在标签表中退出。不要创建标签，但仍然在CompanyTags表中创建关系

How to configure so when a new company gets created and if the tag exits in the Tag table. Dont create the tag but still create the relationship in the CompanyTags table

更新
无需条件，如果用户例如添加标签标题狗，如果它存在在记录表中创建新记录。相反，我不想在映射表中的标签表中创建标签，请参见下面的屏幕截图

UPDATE without if condition, if user for example adds tag title dog and if it exists a new record gets created in the tag table. Instead I want no tag to be created in the tag table just in the mapping table, see screenshot below

推荐答案

通过实现解决

       _db.Tags.FirstOrDefault(x => x.Title == tag) 

而不是做新的标签...

instead of doing new Tags...

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