c# – 在Entity Framework中有什么是Include()方法的工作

我有两个实体权限和访问权限

Access.cs

public class Access
{
    public int Id { get; set; }

    public string Name { get; set; }

    public List<Permission> PermissionList { get; set; }
}

Permission.cs

public class Permission
{
    public int Id { get; set; }

    public string Name { get; set; }

    public int ParentId { get; set; }

    [NotMapped]
    public bool HasChildren { get; set; }

    [NotMapped]
    public List<Permission> ChildPermissions { get; set; }
}

我还有GenericRepository类来过滤我的数据库中的记录.

GenericRepository.cs

public virtual IEnumerable<TEntity> Get(
            Expression<Func<TEntity,bool>> filter = null,Func<IQueryable<TEntity>,IOrderedQueryable<TEntity>> orderBy = null,string includeProperties = "",bool tracking = true)
        {
            IQueryable<TEntity> query = dbSet;


            if (filter != null)
            {
                query = query.Where(filter);
            }

            foreach (var includeProperty in includeProperties.Split
                (new char[] { ',' },StringSplitOptions.RemoveEmptyEntries))
            {
                query = query.Include(includeProperty);
            }
        /*...*/
        }

我在Access Service类中调用此方法

AccessService.cs

GenericRepository<Access> accessRepo = new GenericRepository<Access>();
List<Access> accessList = accessRepo.Get(d => d.Name == accessName,null,"PermissionList").OrderBy(d => d.Id).ToList();

此代码过滤记录类型的“Access”,然后在Generic Repository中使用Include()方法和“PermissionList”参数.什么是包含(“PermissionList”)方法的工作？
它有什么作用？ PermissionList是Access的一个属性,其元素类型为Permission.但我无法完全了解它的目标.

解决方法

它是为了热切地加载相关实体.

见Entity Framework Loading Related Entities.

当不使用Include()时,此查询：

using (var context = new YourContext())
{
    var access = context.Access.Single(a => a.ID == 42);    
}

将返回具有空PermissionList属性的Access实例.根据您的上下文的配置方式,此集合将保持为空(无延迟加载),或者一旦访问它就会延迟加载(foreach(access.PermissionList中的var权限){…}).

现在使用Include()：

using (var context = new YourContext())
{
    var access = context.Access.Include(a => a.PermissionList)
                               .Single(a => a.ID == 42);    
}

查询将写为联接,为您加载所有相关权限.

Include()扩展方法也有一个字符串重载,您的存储库代码正在调用它：

query = query.Include(includeProperty);

这会导致您的情况“PermissionList”被急切加载,并且它似乎使用逗号分隔列表(例如“PermissionList,PermissionList.ChildPermissions”)支持多个Include().

原文地址：https://www.jb51.cc/csharp/98002.html