EF中一对多的自反关系设置
2014-02-27 23:06 左眼微笑右眼泪 阅读(596) 评论(0) 编辑 收藏 举报对于一般的目录树,通常就是一对多的自反关系,一般会有一个PID,引用于这个ID,实体类代码类似于下:
public partial class Catalog
{
public Catalog()
{
this.References = new List<Reference>();
this.Children = new List<Catalog>();
}
public string CatalogID { get; set; }
public string CatalogName { get; set; }
public string CatalogPID { get; set; }
public ICollection<Reference> References { get; set; }
public virtual Catalog Parent { get; set; }
public virtual ICollection<Catalog> Children { get; set; }
}
实体类中会有一个孩子节点的集合,然后有一个父节点的实体;Map文件映射如下:
public CatalogMap()
{
// Primary Key
this.HasKey(t => t.CatalogID);
// Properties
this.Property(t => t.CatalogID)
.IsRequired()
.HasMaxLength(36);
this.Property(t => t.CatalogName)
.HasMaxLength(100);
this.Property(t => t.CatalogPID)
.IsOptional();
// Table & Column Mappings
this.ToTable("Catalog");
this.Property(t => t.CatalogID).HasColumnName("CatalogID");
this.Property(t => t.CatalogID).HasColumnName("CatalogPID");
this.Property(t => t.CatalogName).HasColumnName("CatalogName");
//Relationships
//this.HasMany(t => t.References)
// .WithOptional(t => t.Catalog)
// .HasForeignKey(d => d.CatalogID);
this.HasOptional(t => t.Parent)
.WithMany(t => t.Children)
.HasForeignKey(d => d.CatalogPID);
}
一定要注意以下的这段代码:
this.Property(t => t.CatalogPID)
.IsOptional();
它的意思是允许这个外键为空,因为一般情况下,根结点的父ID一般都会为空。如果设置为必须的话,那么根结点的父ID就不知道设置成什么值了。否则的话,在程序中就会报错:“because all of the properties in the Dependent Role are non-nullable, multiplicity of the Principal Role must be 1”.