NHibernate 3 或 4 等效于实体框架包括

Question

NHibernate 3 或 4 是否等效于实体框架的"Include"方法，该方法采用字符串参数而不是 llambda？ 我想在NHibernate中做这样的事情：

Contact contact =
        context.Contacts.Include("SalesOrderHeaders.SalesOrderDetails")
        .FirstOrDefault();

我从这篇文章中遇到了这段代码，它在循环中使用"Fetch"很酷，但这只处理作为主对象的一级子级的对象，而上面的 EF 代码下降 2 级，不需要强类型的 llambdas。

public IQueryable<T> All<T>(params Expression<Func<T, Object>> [] fetchPaths)
{
    var queryable = this.session.Query<T>();
    foreach (var fetchPath in fetchPaths)
    {
        queryable = queryable.Fetch(fetchPath);
    }
    return queryable;
}

Answer 1

NHibernate有第二个方法称为ThenFetch。你将不得不写

this.session.Query<T>()
            .Fetch(x => x.Property)
            .ThenFetch(x => x.SubProperty);

Answer 2

似乎有几个选项可以解决我的问题。

选项 1：以以下形式动态构建 HQL：

from Contacts t0
left join fetch t0.SalesOrderHeaders t1
left join fetch t1.SalesOrderDetails t2

选项 2：使用 NHibernate 的 ICriteria.SetFetchMode。 这可以处理基于字符串的连接，这非常有用，并且比 HQL 方法更容易实现我的目的。 这是我最终编写的代码（改编自这篇文章）。 我希望这对其他人有帮助。 "GetPathsToUse"方法是我尝试使用实体框架样式的包含路径。 因此，如果我想提供"SalesOrderHeaders.SalesOrderDetails"作为唯一的路径，该方法会在"SalesOrderHeaders.SalesOrderDetails"之前先添加"SalesOrderHeaders"，以便NH会很高兴。

// This also uses ICriteria, but adds some logic to auto-handle paths to reduce the number of paths needed to pass in to match how 
        // EntityFramework works e.g. if one path is passed in for OrderInputs.Input, this method will call SetFetchMode twice, once for OrderInputs and again for OrderInputs.Input
        public T GetByIdSetFetchModeEFStyle(Guid id, ISession session, params string[] includePaths)
        {   
            ICriteria criteria = session.CreateCriteria<T>();
            if (includePaths != null && includePaths.Length > 0)
            {
                // NHibernate requires paths to be supplied in order.  So if a path "OrderInputs.Input" is supplied, we must make 
                // 2 separate calls to SetFetchMode, the first with "OrderInputs", and the second with "OrderInputs.Input".
                // EntityFramework handles this for us, but NHibernate requires things to be different.
                List<string> pathsToUse = this.GetPathsToUse(includePaths);
                foreach (string path in pathsToUse)
                {
                    criteria.SetFetchMode(path, FetchMode.Eager);
                }
            }
            return criteria
                // prevent duplicates in the results
                .SetResultTransformer(Transformers.DistinctRootEntity)
                .Add(Restrictions.Eq(typeof(T).Name + "Id", id)).UniqueResult<T>();
        }
        private List<string> GetPathsToUse(string[] includePaths)
        {
            var nhPaths = new List<string>();
            foreach (string path in includePaths)
            {
                if (!path.Contains(".") && !nhPaths.Contains(path))
                {
                    // There is no dot in the path - just add it if it hasn't been added already
                    nhPaths.Add(path);
                }
                else
                {
                    // We have a dot e.g. OrderInputs.Input.  We need to add "OrderInputs" before "OrderInputs.Input"
                    string[] pathParts = path.Split(".".ToCharArray());
                    // Add any missing ancestors of the current path prior to adding the path
                    for (int p = 1; p <= pathParts.Length; p++)
                    {
                        string requiredPath = string.Join(".", pathParts.Take(p).ToArray());
                        if (!nhPaths.Contains(requiredPath))
                        {
                            nhPaths.Add(requiredPath);
                        }
                    }
                }
            }
            return nhPaths;
        }