Linq IQueryable通用筛选器
本文关键字:筛选 IQueryable Linq | 更新日期: 2023-09-27 18:24:45
我正在为任何列/字段映射的查询中的searchText寻找一个通用筛选器
public static IQueryable<T> Filter<T>(this IQueryable<T> source, string searchTerm)
{
var propNames = typeof(T).GetProperties(BindingFlags.Instance | BindingFlags.Public).Where(e=>e.PropertyType == typeof(String)).Select(x => x.Name).ToArray();
//I am getting the property names but How can I create Expression for
source.Where(Expression)
}
这里我给你举一个的例子
现在,从我在Asp.net MVC4中的HTML5表中,我提供了一个搜索框来过滤输入文本的结果,它可以匹配下面的任何列/Menu类属性值,我想在服务器端进行搜索,我如何实现它。
EF模型类
public partial class Menu
{
public int Id { get; set; }
public string MenuText { get; set; }
public string ActionName { get; set; }
public string ControllerName { get; set; }
public string Icon { get; set; }
public string ToolTip { get; set; }
public int RoleId { get; set; }
public virtual Role Role { get; set; }
}
您可以使用表达式:
private static Expression<Func<T, bool>> GetColumnEquality<T>(string property, string term)
{
var obj = Expression.Parameter(typeof(T), "obj");
var objProperty = Expression.PropertyOrField(obj, property);
var objEquality = Expression.Equal(objProperty, Expression.Constant(term));
var lambda = Expression.Lambda<Func<T, bool>>(objEquality, obj);
return lambda;
}
public static IQueryable<T> Filter<T>(IQueryable<T> source, string searchTerm)
{
var propNames = typeof(T).GetProperties(BindingFlags.Instance | BindingFlags.Public)
.Where(e => e.PropertyType == typeof(string))
.Select(x => x.Name).ToList();
var predicate = PredicateBuilder.False<T>();
foreach(var name in propNames)
{
predicate = predicate.Or(GetColumnEquality<T>(name, searchTerm));
}
return source.Where(predicate);
}
与NutShell中C#中的名称PredicateBuilder
组合。这也是LinqKit的一部分。
示例:
public class Foo
{
public string Bar { get; set; }
public string Qux { get; set; }
}
Filter<Foo>(Enumerable.Empty<Foo>().AsQueryable(), "Hello");
// Expression Generated by Predicate Builder
// f => ((False OrElse Invoke(obj => (obj.Bar == "Hello"), f)) OrElse Invoke(obj => (obj.Qux == "Hello"), f))
void Main()
{
// creates a clause like
// select * from Menu where MenuText like '%ASD%' or ActionName like '%ASD%' or....
var items = Menu.Filter("ASD").ToList();
}
// Define other methods and classes here
public static class QueryExtensions
{
public static IQueryable<T> Filter<T>(this IQueryable<T> query, string search)
{
var properties = typeof(T).GetProperties().Where(p =>
/*p.GetCustomAttributes(typeof(System.Data.Objects.DataClasses.EdmScalarPropertyAttribute),true).Any() && */
p.PropertyType == typeof(String));
var predicate = PredicateBuilder.False<T>();
foreach (var property in properties )
{
predicate = predicate.Or(CreateLike<T>(property,search));
}
return query.AsExpandable().Where(predicate);
}
private static Expression<Func<T,bool>> CreateLike<T>( PropertyInfo prop, string value)
{
var parameter = Expression.Parameter(typeof(T), "f");
var propertyAccess = Expression.MakeMemberAccess(parameter, prop);
var like = Expression.Call(propertyAccess, "Contains", null, Expression.Constant(value,typeof(string)));
return Expression.Lambda<Func<T, bool>>(like, parameter);
}
}
您需要添加对LinqKit的引用才能使用PredicateBuilder和AsExpandable方法否则将无法使用EF,只能使用Linq到SQL
如果需要Col1 like '%ASD%' AND Col2 like '%ASD%' et
,请将PredicateBuilder.False
更改为PredicateBuilder.True
,将predicate.Or
更改为predicate.And
此外,您还需要找到一种方法,通过自己的自定义属性(例如在分部类中定义)来区分映射的属性