LINQ动态组合查询
最近在项目中用到了LINQ，在界面上有许多组合查询条件，我是一个比较懒的人，呵呵，不想在数据查询层写许多方法。我自己尝试写了个Expression的LINQ动态查询，目的是到达了，但是我在代码的初始表达式为null，每次组合AND前都要判断是否为空，为空则返回右边的表达式。今天在网上Google了一下，看到肖坤：Linq动态查询与模糊查询（带源码示例）中讲到的《dynamic linq queries / dynamic where clause (part 2) 》，中老外写的PredicateExtensions类。便用这个类修改了下自己的方案。不在是全表达式树动态生成了。今天特地写了一个基于Northwind的Demo拿来和大家分享：
效果贴图：
界面是用Telerik控件做的（控件对于我们后台开发人员来说就是少调样式）。
代码：
代码
using
System;
using System.Web.UI;
using System.Linq.Expressions;
public partial class _Default : System.Web.UI.Page
{
private OrderController controller = new OrderController();
protected void Page_Load( object sender, EventArgs e)
{
if ( ! IsPostBack)
{
Bindgrid( null );
}
}
public void Bindgrid(Expression < Func < Orders, bool >> whereqQuery)
{
grid.DataSource = controller.GetOrders( 1 , 15 , whereqQuery,
new QueryableOrderEntry < Orders,
string > (t => t.CustomerID, OrderDirection.DESC)); // 分页数目应该用分页控件，
这里只是简单测试，所以偷个懒
grid.DataBind();
}
protected void btnSearch_Click( object sender, ImageClickEventArgs e)
{
Expression < Func < Orders, bool >> expression = PredicateExtensions.True < Orders > ();
if ( ! string .IsNullOrEmpty(txtCustomerId.Text.Trim()))
{
string str = txtCustomerId.Text.Trim();
expression = expression.And(o => o.CustomerID.Contains(str));
}
if ( ! string .IsNullOrEmpty(txtEmplyeeId.Text.Trim()))
{
string str = txtEmplyeeId.Text.Trim();
expression = expression.And(o => o.EmployeeID.HasValue &&
o.EmployeeID.Value.Equals( int .Parse(str)));
}
if (txtOrderDateStart.SelectedDate.HasValue)
{DateTime dt = txtOrderDateStart.SelectedDate.Value;
expression = expression.And(o => o.OrderDate.HasValue
&& o.OrderDate.Value >= dt);
}
if (txtOrderDateEnd.SelectedDate.HasValue)
{
DateTime dt = txtOrderDateEnd.SelectedDate.Value;
expression = expression.And(o => o.OrderDate.HasValue
&& o.OrderDate.Value <= dt);
}
Bindgrid(expression);
}
}
using System.Web.UI;
using System.Linq.Expressions;
public partial class _Default : System.Web.UI.Page
{
private OrderController controller = new OrderController();
protected void Page_Load( object sender, EventArgs e)
{
if ( ! IsPostBack)
{
Bindgrid( null );
}
}
public void Bindgrid(Expression < Func < Orders, bool >> whereqQuery)
{
grid.DataSource = controller.GetOrders( 1 , 15 , whereqQuery,
new QueryableOrderEntry < Orders,
string > (t => t.CustomerID, OrderDirection.DESC)); // 分页数目应该用分页控件，
这里只是简单测试，所以偷个懒
grid.DataBind();
}
protected void btnSearch_Click( object sender, ImageClickEventArgs e)
{
Expression < Func < Orders, bool >> expression = PredicateExtensions.True < Orders > ();
if ( ! string .IsNullOrEmpty(txtCustomerId.Text.Trim()))
{
string str = txtCustomerId.Text.Trim();
expression = expression.And(o => o.CustomerID.Contains(str));
}
if ( ! string .IsNullOrEmpty(txtEmplyeeId.Text.Trim()))
{
string str = txtEmplyeeId.Text.Trim();
expression = expression.And(o => o.EmployeeID.HasValue &&
o.EmployeeID.Value.Equals( int .Parse(str)));
}
if (txtOrderDateStart.SelectedDate.HasValue)
{DateTime dt = txtOrderDateStart.SelectedDate.Value;
expression = expression.And(o => o.OrderDate.HasValue
&& o.OrderDate.Value >= dt);
}
if (txtOrderDateEnd.SelectedDate.HasValue)
{
DateTime dt = txtOrderDateEnd.SelectedDate.Value;
expression = expression.And(o => o.OrderDate.HasValue
&& o.OrderDate.Value <= dt);
}
Bindgrid(expression);
}
}
其中其实很简单，主要方法就两个，一个事表达式树组合，和数据绑定。数据绑定，有一个
Expression<Func<Orders, bool>> 的where查询条件。
Controller类Code：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Linq.Expressions;
using System.Diagnostics;
public class OrderController
{
protected NorthwindDataContext DataContext
{
get
{
NorthwindDataContext context =
HttpContext.Current.Items[ " NorthwindDataContext " ]
as NorthwindDataContext;
if (context == null )
{
context = new NorthwindDataContext();
HttpContext.Current.Items[ " NorthwindDataContext " ] = context;
}
return context;
}
}
public List < Orders > GetOrders < TKey > ( int currentPage,
int pagesize, Expression < Func < Orders, bool >> whereQuery,
QueryableOrderEntry < Orders, TKey > orderQuery)
// 重点在这里的参数
{
IQueryable < Orders > query = DataContext.Orders;
if (whereQuery != null )
{
query = query.Where(whereQuery);
}
if (orderQuery != null )
{
if (orderQuery.OrderDirection == OrderDirection.ASC)
{
query = query.OrderBy(orderQuery.Expression);
}
else
{
query = query.OrderByDescending(orderQuery.Expression);
}
}
Debug.WriteLine(DataContext.GetCommand(query.Skip((currentPage - 1 ) * pagesize)
.Take(pagesize)).CommandText);
return query.Skip((currentPage - 1 ) * pagesize).Take(pagesize).ToList();
}
public void Save()
{
DataContext.SubmitChanges();
}
}
我的排序辅助类：
using System;
using System.Linq.Expressions;
public class QueryableOrderEntry < TSource, TKey >
{
public QueryableOrderEntry(Expression < Func < TSource, TKey >> expression)
{
this .Expression = expression;
OrderDirection = OrderDirection.ASC;
}
public QueryableOrderEntry(Expression < Func < TSource, TKey >> expression,
OrderDirection orderDirection)
{
this .Expression = expression;
OrderDirection = orderDirection;
}
public Expression < Func < TSource, TKey >> Expression
{
get ;
set ;
}
public OrderDirection OrderDirection
{
get ;
set ;
}
}
public enum OrderDirection
{
ASC, DESC
}
老外的PredicateExtensions类很简单，只是真的思路很优秀，看到代码我们都会恍然大悟，
但是估计我这鼠辈很难想到。
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);
}
}
sql看不全：故在这里也贴一个：
SELECT TOP ( 15 ) [ t0 ] . [ OrderID ] , [ t0 ] . [ CustomerID ] , [ t0 ] . [ EmployeeID ] , [ t0 ] . [ OrderDate ] ,
[ t0 ] . [ RequiredDate ] , [ t0 ] . [ ShippedDate ] , [ t0 ] . [ ShipVia ] , [ t0 ] . [ Freight ] , [ t0 ] . [ ShipName ] ,
[ t0 ] . [ ShipAddress ] , [ t0 ] . [ ShipCity ] , [ t0 ] . [ ShipRegion ] , [ t0 ] . [ ShipPostalCode ] ,
[ t0 ] . [ ShipCountry ] FROM [ dbo ] . [ Orders ] AS [ t0 ]
WHERE ( [ t0 ] . [ CustomerID ] LIKE @p0 ) AND ( [ t0 ] . [ EmployeeID ] IS NOT NULL ) AND
(( [ t0 ] . [ EmployeeID ] ) = @p1 ) AND ( [ t0 ] . [ OrderDate ] IS NOT NULL ) AND
(( [ t0 ] . [ OrderDate ] ) >= @p2 ) AND ( [ t0 ] . [ OrderDate ] IS NOT NULL ) AND
(( [ t0 ] . [ OrderDate ] ) <= @p3 ) ORDER BY [ t0 ] . [ CustomerID ] DESC
在这里说老外的思想优秀，该讲解一下，但是限于篇幅，还有时间凌晨1点了，故改到下回讲解。
附带：本随笔代码下载