LINQ Expression< Func> T，bool>等同于.Contains() [英] LINQ Expression<Func<T, bool>> equavalent of .Contains()

问题描述

有人知道如何使用Linq表达式创建.Contains(string)函数，甚至创建谓词来实现这一目标

Has anybody got an idea of how to create a .Contains(string) function using Linq Expressions, or even create a predicate to accomplish this

public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expr1,
      Expression<Func<T, bool>> expr2)
{
    var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
    return Expression.Lambda<Func<T, bool>>
               (Expression.OrElse(expr1.Body, invokedExpr), expr1.Parameters);
}

与此类似的东西是理想的吗?

Something simular to this would be ideal?

推荐答案

public static Expression<Func<string, bool>> StringContains(string subString)
{
    MethodInfo contains = typeof(string).GetMethod("Contains");
    ParameterExpression param = Expression.Parameter(typeof(string), "s");
    var call = Expression.Call(param, contains, Expression.Constant(subString, typeof(string)));
    return Expression.Lambda<Func<string, bool>>(call, param);
}

...

// s => s.Contains("hello")
Expression<Func<string, bool>> predicate = StringContains("hello");

---

回顾了多年之后，我突然意识到对于这个特定示例，有一种更简单的方法:

---

Looking at this many years later, I suddenly realize there's a much simpler approach for this specific example:

Expression<Func<string, bool>> predicate = s => s.Contains("hello");

这篇关于LINQ Expression< Func> T，bool>等同于.Contains()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！