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copied!<p>I created 2 extension methods <code>WhereFilter()</code> for <code>IEnumerable</code> and <code>IQueryable</code>. At this way you can use this filter also with e.g. Entity Framework and is the filtering performed on the server.</p> <p>I used a filter based on <em>*</em> (not ?) so i could use the underlaying Linq methods <code>StartsWith()</code>, <code>EndsWith()</code> and <code>Contains()</code>. Supported formats: A*, *A, *A*, A*B </p> <p>Usage:</p> <pre><code>var filtered = list.WhereFilter(i => i.Name, "a*", "First Name"); </code></pre> <p>Here the basics of the class:</p> <pre><code>/// <summary> /// Extension Methods for Filtering on IQueryable and IEnumerable /// </summary> internal static class WhereFilterExtensions { /// <summary> /// Filters a sequence of values based on a filter with asterix characters: A*, *A, *A*, A*B /// </summary> /// <param name="source"></param> /// <param name="selector">Field to use for filtering. (E.g: item => item.Name)</param> /// <param name="filter">Filter: A*, *A, *A*, A*B</param> /// <param name="fieldName">Optional description of filter field used in error messages</param> /// <returns>Filtered source</returns> public static IEnumerable<T> WhereFilter<T>(this IEnumerable<T> source, Func<T, string> selector, string filter, string fieldName) { if (filter == null) return source; if (selector == null) return source; int astrixCount = filter.Count(c => c.Equals('*')); if (astrixCount > 2) throw new ApplicationException(string.Format("Invalid filter used{0}. '*' can maximum occur 2 times.", fieldName == null ? "" : " for '" + fieldName + "'")); if (filter.Contains("?")) throw new ApplicationException(string.Format("Invalid filter used{0}. '?' is not supported, only '*' is supported.", fieldName == null ? "" : " for '" + fieldName + "'")); // *XX* if (astrixCount == 2 && filter.Length > 2 && filter.StartsWith("*") && filter.EndsWith("*")) { filter = filter.Replace("*", ""); return source.Where(item => selector.Invoke(item).Contains(filter)); } // *XX if (astrixCount == 1 && filter.Length > 1 && filter.StartsWith("*")) { filter = filter.Replace("*", ""); return source.Where(item => selector.Invoke(item).EndsWith(filter)); } // XX* if (astrixCount == 1 && filter.Length > 1 && filter.EndsWith("*")) { filter = filter.Replace("*", ""); return source.Where(item => selector.Invoke(item).StartsWith(filter)); } // X*X if (astrixCount == 1 && filter.Length > 2 && !filter.StartsWith("*") && !filter.EndsWith("*")) { string startsWith = filter.Substring(0, filter.IndexOf('*')); string endsWith = filter.Substring(filter.IndexOf('*') + 1); return source.Where(item => selector.Invoke(item).StartsWith(startsWith) && selector.Invoke(item).EndsWith(endsWith)); } // XX if (astrixCount == 0 && filter.Length > 0) { return source.Where(item => selector.Invoke(item).Equals(filter)); } // * if (astrixCount == 1 && filter.Length == 1) return source; // Invalid Filter if (astrixCount > 0) throw new ApplicationException(string.Format("Invalid filter used{0}.", fieldName == null ? "" : " for '" + fieldName + "'")); // Empty string: all results return source; } /// <summary> /// Filters a sequence of values based on a filter with asterix characters: A*, *A, *A*, A*B /// </summary> /// <param name="source"></param> /// <param name="selector">Field to use for filtering. (E.g: item => item.Name) </param> /// <param name="filter">Filter: A*, *A, *A*, A*B</param> /// <param name="fieldName">Optional description of filter field used in error messages</param> /// <returns>Filtered source</returns> public static IQueryable<T> WhereFilter<T>(this IQueryable<T> source, Expression<Func<T, string>> selector, string filter, string fieldName) { if (filter == null) return source; if (selector == null) return source; int astrixCount = filter.Count(c => c.Equals('*')); if (astrixCount > 2) throw new ApplicationException(string.Format("Invalid filter used{0}. '*' can maximum occur 2 times.", fieldName==null?"":" for '" + fieldName + "'")); if (filter.Contains("?")) throw new ApplicationException(string.Format("Invalid filter used{0}. '?' is not supported, only '*' is supported.", fieldName == null ? "" : " for '" + fieldName + "'")); // *XX* if (astrixCount == 2 && filter.Length > 2 && filter.StartsWith("*") && filter.EndsWith("*")) { filter = filter.Replace("*", ""); return source.Where( Expression.Lambda<Func<T, bool>>( Expression.Call(selector.Body, "Contains", null, Expression.Constant(filter)), selector.Parameters[0] ) ); } // *XX if (astrixCount == 1 && filter.Length > 1 && filter.StartsWith("*")) { filter = filter.Replace("*", ""); return source.Where( Expression.Lambda<Func<T, bool>>( Expression.Call(selector.Body, "EndsWith", null, Expression.Constant(filter)), selector.Parameters[0] ) ); } // XX* if (astrixCount == 1 && filter.Length > 1 && filter.EndsWith("*")) { filter = filter.Replace("*", ""); return source.Where( Expression.Lambda<Func<T, bool>>( Expression.Call(selector.Body, "StartsWith", null, Expression.Constant(filter)), selector.Parameters[0] ) ); } // X*X if (astrixCount == 1 && filter.Length > 2 && !filter.StartsWith("*") && !filter.EndsWith("*")) { string startsWith = filter.Substring(0, filter.IndexOf('*')); string endsWith = filter.Substring(filter.IndexOf('*') + 1); return source.Where( Expression.Lambda<Func<T, bool>>( Expression.Call(selector.Body, "StartsWith", null, Expression.Constant(startsWith)), selector.Parameters[0] ) ).Where( Expression.Lambda<Func<T, bool>>( Expression.Call(selector.Body, "EndsWith", null, Expression.Constant(endsWith)), selector.Parameters[0] ) ); } // XX if (astrixCount == 0 && filter.Length > 0) { return source.Where( Expression.Lambda<Func<T, bool>>( Expression.Equal(selector.Body, Expression.Constant(filter)), selector.Parameters[0] ) ); } // * if (astrixCount == 1 && filter.Length == 1) return source; // Invalid Filter if (astrixCount > 0) throw new ApplicationException(string.Format("Invalid filter used{0}.", fieldName == null ? "" : " for '" + fieldName + "'")); // Empty string: all results return source; } } </code></pre>

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