Question

NHibernate 3或4是否与Entity Framework的“Include”方法等效，它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();

我遇到了来自this post的代码，它在一个很酷的循环中使用“Fetch”，但这只处理作为主要对象的第一级子对象的对象，而上面的EF代码却出现故障2个级别，不需要强烈类型的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有第二个方法叫做ThenFetch。你必须写

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

Answer 2

似乎有几种方法可以解决我的问题。

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，并且比我的目的更容易使用HQL方法。这是我最后编写的代码（改编自this post）。我希望它对别人有帮助。＆＃34; GetPathsToUse＆＃34;方法是我尝试使用Entity Framework样式包含路径。所以，如果我想提供＆＃34; SalesOrderHeaders.SalesOrderDetails＆＃34;作为唯一的途径，该方法将添加＆＃34; SalesOrderHeaders＆＃34;第一个＆＃34; SalesOrderHeaders.SalesOrderDetails＆＃34;让NH很开心。

// 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;
        }

NHibernate 3或4等效于实体框架

2 个答案: