在C#中使用string.format生成按子句的lambda表达式? [英] Generate lambda Expression By Clause using string.format in C#?

问题描述

我有一种按子句生成表达式的方法，如下所示:

I have a method to Generate Expression By Clause as below:

internal static Expression<Func<TModel, T>> GenExpressionByClause<TModel, T>(string column)
    {
        PropertyInfo columnPropInfo = typeof(TModel).GetProperty(column);

        var entityParam = Expression.Parameter(typeof(TModel), "e");                    // {e}
        var columnExpr = Expression.MakeMemberAccess(entityParam, columnPropInfo); // {e.column}
        var lambda = Expression.Lambda(columnExpr, entityParam) as Expression<Func<TModel, T>>; // {e => e.column}
        return lambda;

    }

所以我可以将lambda表达式构建为e=>e.column. 但我想将其更改为e=>string.Format("{0}",e.column).我该如何重构代码?

So I could build lambda expression as e=>e.column. but I want to change it to e=>string.Format("{0}",e.column). How could I refactor the code?

推荐答案

这应该可以完成工作:

    internal static Expression<Func<TModel, T>> GenExpressionByClause<TModel, T>(string column)
    {
        var columnPropInfo = typeof(TModel).GetProperty(column);
        var formatMethod = typeof (string).GetMethod("Format", new[] {typeof (string), typeof (object)});

        var entityParam = Expression.Parameter(typeof(TModel), "e");
        var columnExpr = Expression.MakeMemberAccess(entityParam, columnPropInfo);
        var formatCall = Expression.Call( formatMethod, Expression.Constant("{0}"), columnExpr);
        var lambda = Expression.Lambda(formatCall , entityParam) as Expression<Func<TModel, T>>;
        return lambda;
    }

请注意，您可以将FormatMethodInfo格式缓存在静态字段中.

Note that you could cache the Format MethodInfo in a static field.

这篇关于在C#中使用string.format生成按子句的lambda表达式?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！