How to create predicate dynamically
Solution 1
Initialize the predicate as false
Expression<Func<products, bool>> predicate = PredicateBuilder.False<products>();
You need to combine the predicates using Or
foreach (string str in SearchItems)
{
string temp = str;
predicate = predicate.Or(p => p.NameToLower().Contains(temp.ToLower()));
}
Source for predicate builder here. It is part of LINQKit
Code, in case link goes
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);
}
}
Solution 2
You don't have to build a predicate here. You can try something like this
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"));
string input = "aaa+kuma+ram";
List<string> searchStrings =
input.Split(new string[] { "+" }, StringSplitOptions.None)
.Select(s => s.ToLower())
.ToList();
List<products> list2 = (
from p in list1
where searchStrings.Any(s => p.Name.Contains(s))
select p).ToList();
list2 will contain "kumar" and "ramya".
Solution 3
As I am not sure that predicate instance has an And method, I suggest you use this code:
var list = list1.AsQueryable();
foreach (string str in SearchItems)
{
list = list.Where(p => p.Name.ToLower().Contains(str.ToLower()));
}
listBox1.ItemsSource = list.ToList();
Comments
-
Sowmya almost 2 years
Hi i want to create a list based on the search string using predicate expressions.
I have a list of type products contains different names.
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;
Now i want to filter the content based on user input.User will enter n no of strings with '+' as separator. After receiving the strings i will pass them to predicate object like this
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; } }
If i enter more than one string(sowmya+jane+john) its giving only the last string(john) result but i want a list of all matching strings
Please answer this question because i'm trying this but i couldn't get the result.
Please do some help thanks.
-
Sowmya almost 13 yearsif i use this code its giving only one string result but if i enter two strings its not giving any result.Please find the solution.I need it.
-
Maziar Taheri almost 13 yearsthat might be because of the first
.ToLower()
I just added. if not make sure yourName
property really contains both of the strings you search for -
Sowmya almost 13 yearsIf i use And to combine predicates its giving all the list items but not the matching string result
-
Sowmya almost 13 yearssame issue again giving the last string result only.Ya i'm sure The "Name" property contains both the strings
-
Sowmya almost 13 yearsThank u and this will work and working also i knew that but i need to construct it by using predicate only please help me
-
Maziar Taheri almost 13 yearsyou should check if you have copied and pasted the code correctly then.
-
Eranga almost 13 years@Sowmya updated my answer. you need to use
temp
notstr
inside the predicate -
Gebb almost 13 years@Sowmya then you should try what Eranga suggests.
-
Sowmya almost 13 yearsHey Eranga thank you soooo much its working fine. Really you helped me
-
wtf512 about 7 yearsIs this
predicatebuilder
the same to this article albahari.com/nutshell/predicatebuilder.aspx? -
Shimmy Weitzhandler about 6 years
PredicateBuilder
?