A predicate builder can be used to dynamically add conditions to a linq query.
The class is
And it can be used like:
The complete source code can be found at http://www.albahari.com/nutshell/predicatebuilder.aspx
The class is
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); } }
And it can be used like:
var predicate = PredicateBuilder.False<Product>(); foreach (string keyword in keywords) { string temp = keyword; predicate = predicate.Or (p => p.Description.Contains (temp)); }
The complete source code can be found at http://www.albahari.com/nutshell/predicatebuilder.aspx