AppBox升级进行时 - 如何向OrderBy传递字符串参数(Entity Framework)

AppBox 是基于 FineUI 的通用权限管理框架,包括用户管理、职称管理、部门管理、角色管理、角色权限管理等模块。

 

Entity Framework提供的排序功能

 再来回顾一下上篇文章,加载用户列表并进行排序数据库分页的代码

var q = DB.Users.Include(u => u.Dept);
 
// 在用户名称中搜索
string searchText = ttbSearchMessage.Text.Trim();
if (!String.IsNullOrEmpty(searchText))
{
    q = q.Where(u => u.Name.Contains(searchText) || u.ChineseName.Contains(searchText) || u.EnglishName.Contains(searchText));
}
 
// 过滤启用状态
if (rblEnableStatus.SelectedValue != "all")
{
    q = q.Where(u => u.Enabled == (rblEnableStatus.SelectedValue == "enabled" ? true : false));
}
 
// 在查询添加之后,排序和分页之前获取总记录数
Grid1.RecordCount = q.Count();
 
// 排列
q = q.OrderBy(u => u.Name);
 
// 数据库分页
q = q.Skip(Grid1.PageIndex * Grid1.PageSize).Take(Grid1.PageSize);
 
Grid1.DataSource = q;
Grid1.DataBind();

让我们把关注点集中到排序代码上:

q = q.OrderBy(u => u.Name);

 

在FineUI实际应用中,我们一般是从表格的 SortField 中读取排序字段,显然EF提供的OrderBy无法接受字符串表示的排序字段。

 

手工创建Lamba表达式  

通过搜索发现了这个帖子:http://stackoverflow.com/questions/10072250/generic-funct-k-to-sort-collections-of-different-types/10074873

据此我们可以写出如下的代码:

public Expression<Func<T, To>> GetSortExpression<T, To>(String sortBy)
{
    var param = Expression.Parameter(typeof(T), "x");
    Expression expr = Expression.Property(param, sortBy);
    return Expression.Lambda<Func<T, To>>(expr, param);
}
 
 
protected IQueryable<T> Sort<T>(IQueryable<T> q, FineUI.Grid grid)
{
    string sortField = grid.SortField;
 
    if (grid.SortDirection == "ASC")
    {
        q = q.OrderBy(GetSortExpression<T, object>(sortField));
    }
    else
    {
        q = q.OrderByDescending(GetSortExpression<T, object>(sortField));
    }
 
    return q;
}

经过测试,我们发现这个方法不支持bool, int, DateTime, DateTime?类型的列排序。

 

经过扩展后的代码如下所示:

protected IQueryable<T> Sort<T>(IQueryable<T> q, FineUI.Grid grid)
{
    string sortField = grid.SortField;
    var propertyType = typeof(T).GetProperty(sortField).PropertyType;
 
    if (grid.SortDirection == "ASC")
    {
        if (propertyType == typeof(bool))
        {
            q = q.OrderBy(GetSortExpression<T, bool>(sortField));
        }
        else if (propertyType == typeof(int))
        {
            q = q.OrderBy(GetSortExpression<T, int>(sortField));
        }
        else if (propertyType == typeof(DateTime))
        {
            q = q.OrderBy(GetSortExpression<T, DateTime>(sortField));
        }
        else if (propertyType == typeof(DateTime?))
        {
            q = q.OrderBy(GetSortExpression<T, DateTime?>(sortField));
        }
        else
        {
            q = q.OrderBy(GetSortExpression<T, object>(sortField));
        }
    }
    else
    {
        if (propertyType == typeof(bool))
        {
            q = q.OrderByDescending(GetSortExpression<T, bool>(sortField));
        }
        else if (propertyType == typeof(int))
        {
            q = q.OrderByDescending(GetSortExpression<T, int>(sortField));
        }
        else if (propertyType == typeof(DateTime))
        {
            q = q.OrderByDescending(GetSortExpression<T, DateTime>(sortField));
        }
        else if (propertyType == typeof(DateTime?))
        {
            q = q.OrderByDescending(GetSortExpression<T, DateTime?>(sortField));
        }
        else
        {
            q = q.OrderByDescending(GetSortExpression<T, object>(sortField));
        }
    }
 
    return q;
}

但这种做法过于臃肿,有没有更好的办法呢?

 

更好的SortBy扩展方法  

后来,我们发现了这篇文章:http://stackoverflow.com/questions/3945645/sorting-gridview-with-entity-framework

通过对 IQueryable<T> 进行扩展,提供了接受类似 "Name DESC", "CreateTime", "CreateTime DESC" 参数的 SortBy 方法,更具有通用性。

原始的SortBy扩展方法:

public static class QueryExtensions {
    public static IQueryable<T> SortBy<T>(this IQueryable<T> source, string propertyName) {
        if (source == null) {
            throw new ArgumentNullException("source");
        }
        // DataSource control passes the sort parameter with a direction
        // if the direction is descending          
        int descIndex = propertyName.IndexOf(" DESC");
        if (descIndex >= 0) {
            propertyName = propertyName.Substring(0, descIndex).Trim();
        }
 
        if (String.IsNullOrEmpty(propertyName)) {
            return source;
        }
 
        ParameterExpression parameter = Expression.Parameter(source.ElementType, String.Empty);
        MemberExpression property = Expression.Property(parameter, propertyName);
        LambdaExpression lambda = Expression.Lambda(property, parameter);
 
        string methodName = (descIndex < 0) ? "OrderBy" : "OrderByDescending";
 
        Expression methodCallExpression = Expression.Call(typeof(Queryable), methodName,
                                            new Type[] { source.ElementType, property.Type },
                                            source.Expression, Expression.Quote(lambda));
 
        return source.Provider.CreateQuery<T>(methodCallExpression);
    }
}

不过这个方法不支持"Name ASC"形式的参数,所以我们进行了简单的修正,修正后的SortBy扩展方法:

public static class QueryExtensions
{
    public static IQueryable<T> SortBy<T>(this IQueryable<T> source, string sortExpression)
    {
        if (source == null)
        {
            throw new ArgumentNullException("source");
        }
 
        string sortDirection = String.Empty;
        string propertyName = String.Empty;
 
        sortExpression = sortExpression.Trim();
        int spaceIndex = sortExpression.Trim().IndexOf(" ");
        if (spaceIndex < 0)
        {
            propertyName = sortExpression;
            sortDirection = "ASC";
        }
        else
        {
            propertyName = sortExpression.Substring(0, spaceIndex);
            sortDirection = sortExpression.Substring(spaceIndex + 1).Trim();
        }
 
        if (String.IsNullOrEmpty(propertyName))
        {
            return source;
        }
 
        ParameterExpression parameter = Expression.Parameter(source.ElementType, String.Empty);
        MemberExpression property = Expression.Property(parameter, propertyName);
        LambdaExpression lambda = Expression.Lambda(property, parameter);
 
        string methodName = (sortDirection == "ASC") ? "OrderBy" : "OrderByDescending";
 
        Expression methodCallExpression = Expression.Call(typeof(Queryable), methodName,
                                            new Type[] { source.ElementType, property.Type },
                                            source.Expression, Expression.Quote(lambda));
 
        return source.Provider.CreateQuery<T>(methodCallExpression);
    }
 
}

  

优化后的排序分页代码

首先在页面基类PageBase中定义排序和分页的代码(使用了前面定义的 SortBy 扩展函数):

protected IQueryable<T> Sort<T>(IQueryable<T> q, FineUI.Grid grid)
{
    return q.SortBy(grid.SortField + " " + grid.SortDirection);
}
 
protected IQueryable<T> SortAndPage<T>(IQueryable<T> q, FineUI.Grid grid)
{
    return Sort(q, grid).Skip(grid.PageIndex * grid.PageSize).Take(grid.PageSize);
}

  

最终查询用户列表的代码:

var q = DB.Users.Include(u => u.Dept);
 
// 在用户名称中搜索
string searchText = ttbSearchMessage.Text.Trim();
if (!String.IsNullOrEmpty(searchText))
{
    q = q.Where(u => u.Name.Contains(searchText) || u.ChineseName.Contains(searchText) || u.EnglishName.Contains(searchText));
}
 
// 过滤启用状态
if (rblEnableStatus.SelectedValue != "all")
{
    q = q.Where(u => u.Enabled == (rblEnableStatus.SelectedValue == "enabled" ? true : false));
}
 
// 在查询添加之后,排序和分页之前获取总记录数
Grid1.RecordCount = q.Count();
 
// 排列和数据库分页
q = SortAndPage<User>(q, Grid1);
 
 
Grid1.DataSource = q;
Grid1.DataBind();

  

 

下载或捐赠AppBox

1. AppBox v2.1 是免费软件,免费提供下载:http://fineui.com/bbs/forum.php?mod=viewthread&tid=3788 

2. AppBox v3.0 是捐赠软件,你可以通过捐赠作者来获取AppBox v3.0的全部源代码(http://fineui.com/donate/)。

 

 

 

posted @ 2013-09-10 10:34 三生石上(FineUI控件) 阅读(...) 评论(...) 编辑 收藏