如何动态创建谓词

Question

您好我想使用谓词表达式基于搜索字符串创建列表.

我有一个类型产品列表包含不同的名称.

List<products> list1 = new List<products>();

        list1.Add(new products("sowmya"));
        list1.Add(new products("Jane"));
        list1.Add(new products("John"));
        list1.Add(new products("kumar"));
        list1.Add(new products("ramya"));
        listBox1.ItemsSource = list1;

现在我想根据用户输入过滤内容.用户将输入n个字符串,并带有'+'作为分隔符.收到字符串后,我会将它们传递给谓词对象

 private void textBox1_KeyDown(object sender, KeyEventArgs e)
    {
        List<products> list2 = new List<products>();
        Expression<Func<products, bool>> predicate = PredicateBuilder.True<products>();
        if (e.Key == Key.Enter)
        {
            string Searchstring = textBox1.Text.ToString().Trim();
            string[] separator = new string[] { "+" };
            string[] SearchItems=Searchstring.Split(separator,StringSplitOptions.None);
            foreach (string str in SearchItems)
            {
                string temp = str;
                predicate =p => p.Name.Contains(temp.ToLower());                   
            }

            list2 = list1.AsQueryable().Where(predicate).ToList();
            listBox1.ItemsSource = list2;
        }
    }

如果我输入多个字符串(sowmya + jane + john),它只给出最后一个字符串(john)结果,但我想要一个所有匹配字符串的列表

请回答这个问题,因为我正在尝试这个,但我无法得到结果.

请帮忙谢谢.

Answer 1

将谓词初始化为false

Expression<Func<products, bool>> predicate = PredicateBuilder.False<products>();

您需要使用组合谓词 Or

foreach (string str in SearchItems)
{
    string temp = str;
    predicate = predicate.Or(p => p.NameToLower().Contains(temp.ToLower()));                   
}

这里谓词构建器的来源.它是LINQKit的一部分

代码,以防链接进行

using System;
using System.Linq;
using System.Linq.Expressions;
using System.Collections.Generic;

public static class PredicateBuilder
{
  public static Expression<Func<T, bool>> True<T> ()  { return f => true;  }
  public static Expression<Func<T, bool>> False<T> () { return f => false; }

  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);
  }

  public static Expression<Func<T, bool>> And<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.AndAlso (expr1.Body, invokedExpr), expr1.Parameters);
  }
}