Question

我希望在数据库的单次往返中执行以下两个查询，因此我使用的是ToFutureValue。

var query = AsQueryable()
    .Where(x => x.User == user);

var singinCount = query
    .Where(x => x.ActionDate >= from && x.ActionDate <= to)
    .ToFutureValue(q => q.Count());

var lastSignin = query
    .Where(x => x.ActionName.ToLower() == Actions.Signin))
    .ToFutureValue(q => q.Max(x => x.ActionDate));

问题是Count和Max返回结果但不返回IQueryable。我找到了以下扩展，使我能够将Count传递给ToFutureValue：

public static IFutureValue<TResult> ToFutureValue<TSource, TResult>(
    this IQueryable<TSource> source, Expression<Func<IQueryable<TSource>, TResult>> selector)
        where TResult : struct
    {
        var provider = (INhQueryProvider)source.Provider;
        var method = ((MethodCallExpression)selector.Body).Method;
        var expression = Expression.Call((Expression)null, method, source.Expression);

        return (IFutureValue<TResult>)provider.ExecuteFuture(expression);
    }

现在我需要为Max采用该扩展名，因为我必须将参数传递给Max（.ToFutureValue（q =＆gt; q.Max（x =＆gt; x.ActionDate）））。我怎么能这样做？

Answer 1

作为解决方法

var lastSignin = query
    .Where(x => x.ActionName.ToLower() == Actions.Signin))
    .OrderByDescending(x => x.ActionDate)
    .Take(1)
    .ToFutureValue();

Answer 2

看起来在GitHub拉取请求中有适当的补丁 #120

这是jira bug NH-3184

以下是拉＃120的代码：

public static IFutureValue<TResult> ToFutureValue<T, TResult>(
    this IQueryable<T> query, Expression<Func<IQueryable<T>, TResult>> selector)
{
    var nhQueryable = query as QueryableBase<T>;    
    if (nhQueryable == null)
    {
        throw new NotSupportedException("Query needs to be of type QueryableBase<T>");
    }


    var provider = (INhQueryProvider) query.Provider;
    var expression = ReplacingExpressionTreeVisitor.Replace(
            selector.Parameters.Single(),
            query.Expression,
            selector.Body);

    return (IFutureValue<TResult>) provider.ExecuteFuture(expression);
}

NHibernate Linq ToFuture和Max

2 个答案: