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尝试使用表达式树创建以下表达式（需要帮助）

List<string> lstName = dt_Name.Select(y => y.Name);

List<string> lstLabName = dt_Label.Select(x => x.LabelName).Where(p => p.LabelName.StartsWith(lstName + '_'));

我希望它实际上遍历所有 lstName 并找到 lstLabName 中满足条件的所有实例。

到目前为止我想出的代码是：

    private BinaryExpression CreateBinaryExpression(string buildName)
    {
        // x.LabelName
        var param = Expression.Parameter(typeof(dt_Label), "x");
        var key = param.GetType().GetProperty("LabelName");
        var left = Expression.MakeMemberAccess(param, key);

        //ParameterExpression left = Expression.Parameter(typeof(string), "p"); //p
        ConstantExpression constantExpression = Expression.Constant(buildName, typeof(string));

        // x.LabelName == buildName
        return Expression.MakeBinary(ExpressionType.Equal, left, constantExpression);
    }

    private BinaryExpression CalculateLambdaExp(List<string> lstBuildName) 
    {
            BinaryExpression binaryExpression = CreateBinaryExpression(lstBuildName[0]);

            if (lstBuildName.Count() > 1)
            {
                List<string> lstnStr = lstBuildName;
                lstnStr.RemoveAt(0);
                BinaryExpression calculatedLambdaExp = CalculateLambdaExp(lstnStr);
                binaryExpression = Expression.MakeBinary(ExpressionType.AndAlso, binaryExpression, calculatedLambdaExp);
            }

            return binaryExpression;
    }

    private List<string> RunLambdaExpression(List<string> BuildName)
    {
        ParameterExpression left = Expression.Parameter(typeof(string), "p"); //p

        var factorial = Expression.Lambda<Func<List<string>, List<string>>>(CalculateLambdaExp(BuildName), left);
        var n = factorial.Compile()(BuildName);
        List<string> lst = n.ToList();

        return lst;
    }

我收到很多运行时错误。将不胜感激任何帮助。

想通了大部分：

将函数 CreateBinaryExpression 更改为：

    private Expression CreateBinaryExpression(string buildName)
    {
        // x.LabelName
        var param = Expression.Parameter(typeof(dt_Label), "x");
        var key = typeof(dt_Label).GetProperty("LabelName");

        var left = Expression.MakeMemberAccess(param, key);

        ConstantExpression constantExpression = Expression.Constant(buildName + '_', typeof(string));

        //x.LabelName.startsWith(buildName_)
        MethodInfo mi = typeof(string).GetMethod("StartsWith", new Type[] { typeof(string) });
        Expression call = Expression.Call(left, mi, constantExpression);

        return call;
    };

并将对该函数的所有引用更改为接收 Expression 而不是 BinaryExpression

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1 回答 1

3

这条线有问题

var key = param.GetType().GetProperty("LabelName");

param.GetType()将返回System.Linq.Expressions.ParameterExpression没有LabelName财产的人。

你应该使用typeof(dt_Label).GetProperty("LabelName")

于 2013-04-11T19:19:18.367 回答