1、添加类PredicateExtensions.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Linq.Expressions;
namespace Www24100Net.PlayingWithLinq
{
public static class PredicateExtensions
{
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>> expression1,
Expression<Func<T, bool>> expression2)
{
var invokedExpression = Expression.Invoke(expression2, expression1.Parameters.Cast<Expression>());
return Expression.Lambda<Func<T, bool>>
(Expression.Or(expression1.Body, invokedExpression), expression1.Parameters);
}
public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expression1,
Expression<Func<T, bool>> expression2)
{
var invokedExpression = Expression.Invoke(expression2, expression1.Parameters.Cast<Expression>());
return Expression.Lambda<Func<T, bool>>
(Expression.And(expression1.Body, invokedExpression), expression1.Parameters);
}
}
}
2、Linq动态查询
private void bind(int pageIndex)
{
if(pageIndex < 1){pageIndex = 1;}
var predicate = PredicateExtensions.True<CityName>();
string _fprovince = "福建";
if (!string.IsNullOrEmpty(_fprovince))
{
predicate = predicate.And(p => p.FProvince.Contains(_fprovince));
}
string _fcity = "厦门";
if (!string.IsNullOrEmpty(_fcity))
{
predicate = predicate.And(p => p.FCity.Contains(_fcity));
}
string _ftype = "联通";
if (!string.IsNullOrEmpty(_ftype))
{
predicate = predicate.And(p => p.FType.Contains(_ftype));
}
DataClassesDataContext DBCity = new DataClassesDataContext();
var query = DBCity.CityName.Where(predicate);
AspNetPager1.RecordCount = query.Count();
this.Label1.Text = AspNetPager1.RecordCount.ToString();
intStartRow = intPageSize * (pageIndex-1) ;
intEndRow = pageIndex * intPageSize;
GridView1.DataSource = query.OrderBy(p => p.FSimseg).Skip(intStartRow).Take(intPageSize);
GridView1.DataBind();
}