我有一个预定义的数据库,我想使用Entity Framework 4 CodeFirst映射.
public class Site
{
public int SiteId { get; set; }
public string SiteName { get; set; }
public DateTime InstallDate { get; set; }
public string Phase { get; set; }
public string Address { get; set; }
public string GpsPosition { get; set; }
public string NetworkDetail { get; set; }
public string SiteCode { get; set; }
public string UserGroupCode { get; set; }
public string InfrastructureNumber { get; set; }
public string Province { get; set; }
public virtual ICollection<LcuSetting> LcuSettings { get; set; }
}
另一堂课
public class LcuSetting
{
public int LCUSettingId { get; set; }
[Column(Name="Site_Id")]
public Site Site { get; set; }
public string Name { get; set; }
public string IPAddress { get; set; }
public string SubnetMask { get; set; }
public string DefaultGateway { get; set; }
}
由于EF4的映射约定,它在表LCUSettings中查找列SiteSiteId,由于Column实际上名为Site_ID,因此无法找到它
在我的DbContext派生类中,我重写OnModelCreating方法并设置要使用的表名.
modelBuilder.Entity<Site>().ToTable("Site");
这很好用.
但是,当我尝试指定列名时,如下所示
modelBuilder.Entity<LcuSetting>().Property(c => c.Site).HasColumnName("Site_Id");
我收到以下异常消息
The type ‘LcuSystemOnline.Models.Site’ must be a non-nullable value type in order to use it as parameter ‘T’ in the generic type or method ‘System.Data.Entity.ModelConfiguration.Configuration.Types.StructuralTypeConfiguration.Property(System.Linq.Expressions.Expression>)’
我理解异常,但是如何让modelBuilder为站点分配特定的ColumnName
解决方法
在CTP5中,您不能使用Column属性指定我们创建的外键名称.您必须使用流畅的API以这种方式执行此操作：
public class Category
{
public int Id { get; set; }
public string Name { get; set; }
public ICollection<Product> Products { get; set; }
}
public class Product
{
public int Id { get; set; }
public string Name { get; set; }
public Category Category { get; set; }
}
public class MyContext : DbContext
{
public DbSet<Product> Products { get; set; }
public DbSet<Category> Categories { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Product>()
.Hasrequired(p => p.Category)
.WithMany(c => c.Products)
.IsIndependent()
.Map(mc => mc.MapKey(c => c.Id,"CategoryId"));
}
}
请注意OnModelCreating方法中对“Map”的调用.这是许多人遇到的问题,我喜欢使用ColumnAttribute来帮助命名.
你可以看到我写的这篇博客文章了解更多细节：
http://blogs.msdn.com/b/adonet/archive/2010/12/10/code-first-mapping-changes-in-ctp5.aspx
