c# - ASP.Net 4.5 模型绑定(bind)按导航属性排序

Question

全部，

我有一个包含以下列的 GridView 。分页效果很好，但不是排序。每次我单击“类别”列以按类别排序时，我都会收到此错误:

实例属性“Category.CategoryName”没有为类型“ESA.Data.Models.Entity.Project”定义

此错误陈述不正确，因为 gridview 能够正确显示该列。

这里是选择方法

    public IQueryable<Project> getProjects()
    {
        ApplicationServices objServices = new ApplicationServices();
        IQueryable<Project> lstProject;
        lstProject = objServices.getProjects();
        return lstProject;
    }

有什么建议吗？

    <asp:GridView ID="grdProject" runat="server" ShowHeader="true" 
        AutoGenerateColumns="false" CellPadding="2" CellSpacing="2" 
        ItemType="ESA.Data.Models.Entity.Project"
        SelectMethod="getProjects"
        DataKeyNames="ProjectID" 
        AllowSorting="true"
        AllowPaging="true"
        PageSize="5">
        <Columns>
            <asp:BoundField DataField="ProjectID" HeaderText="ID " ItemStyle-Width="10" />
            <asp:BoundField DataField="Category.CategoryName" HeaderText="Category" SortExpression="Category.CategoryName" />
            <asp:BoundField DataField="ProjectName" HeaderText="Project Name" ItemStyle-Width="300"  />
            <asp:BoundField DataField="Status.StatusName" HeaderText="Status" SortExpression="Status.StatusName"  />
            <asp:BoundField DataField="AddedByUser.UserName" HeaderText="Added By" ItemStyle-Width="120"  />
            <asp:BoundField DataField="AddedDate" HeaderText="Added Date" ItemStyle-Width="90" DataFormatString="{0:d}"  />
        </Columns>
    </asp:GridView>

Answer 1

我在使用 Listview 控件时遇到了类似的问题。我是这样解决的。

首先，我使用了 Marc Gravell 发表的这篇文章中的代码 Dynamic LINQ OrderBy on IEnumerable<T>

在我的 Listview 的“OnSorting”事件中，我添加了以下代码。

protected void lv_Sorting(object sender, ListViewSortEventArgs e)
{
    e.Cancel = true;
    ViewState["OrderBy"] = e.SortExpression;
    lvList.DataBind();
}

我添加了一个相当标准的方法来捕获这个 sortdirection 列表

public SortDirection sortDirection
{
    get
    {
        if (ViewState["sortdirection"] == null)
        {
            ViewState["sortdirection"] = SortDirection.Ascending;
            return SortDirection.Ascending;
        }
        else if ((SortDirection)ViewState["sortdirection"] == SortDirection.Ascending)
        {
            ViewState["sortdirection"] = SortDirection.Descending;
            return SortDirection.Descending;
        }
        else
        {
            ViewState["sortdirection"] = SortDirection.Ascending;
            return SortDirection.Ascending;
        }
    }
    set
    {
        ViewState["sortdirection"] = value;
    }
}

在我的 Listview 中，Selectmethod 看起来像这样(使用 Marc 的扩展方法)

public IQueryable<SomeObject> GetObjects([ViewState("OrderBy")]String OrderBy = null)
{
    var list = GETSOMEOBJECTS();
    if (OrderBy != null)
    {
        switch (sortDirection)
        {
            case SortDirection.Ascending:
                list = list.OrderByDescending(OrderBy);
                break;
            case SortDirection.Descending:
                list = list.OrderBy(OrderBy);
                break;
            default:
                list = list.OrderByDescending(OrderBy);
                break;
        }
    }
    return list;
}

我还没有用 GridView 尝试过，但我很确定它会工作得一样。

编辑这是应该工作的 linq 扩展类的示例

public static class LinqExtensions
{
    public static IOrderedQueryable<T> OrderBy<T>(this IQueryable<T> source, string property)
    {
        return ApplyOrder<T>(source, property, "OrderBy");
    }
    public static IOrderedQueryable<T> OrderByDescending<T>(this IQueryable<T> source, string property)
    {
        return ApplyOrder<T>(source, property, "OrderByDescending");
    }
    public static IOrderedQueryable<T> ThenBy<T>(this IOrderedQueryable<T> source, string property)
    {
        return ApplyOrder<T>(source, property, "ThenBy");
    }
    public static IOrderedQueryable<T> ThenByDescending<T>(this IOrderedQueryable<T> source, string property)
    {
        return ApplyOrder<T>(source, property, "ThenByDescending");
    }
    static IOrderedQueryable<T> ApplyOrder<T>(IQueryable<T> source, string property, string methodName)
    {
        string[] props = property.Split('.');
        Type type = typeof(T);
        ParameterExpression arg = Expression.Parameter(type, "x");
        Expression expr = arg;
        foreach (string prop in props)
        {
            // use reflection (not ComponentModel) to mirror LINQ
            PropertyInfo pi = type.GetProperty(prop);
            expr = Expression.Property(expr, pi);
            type = pi.PropertyType;
        }
        Type delegateType = typeof(Func<,>).MakeGenericType(typeof(T), type);
        LambdaExpression lambda = Expression.Lambda(delegateType, expr, arg);

        object result = typeof(Queryable).GetMethods().Single(
                method => method.Name == methodName
                        && method.IsGenericMethodDefinition
                        && method.GetGenericArguments().Length == 2
                        && method.GetParameters().Length == 2)
                .MakeGenericMethod(typeof(T), type)
                .Invoke(null, new object[] { source, lambda });
        return (IOrderedQueryable<T>)result;
    } 
}

只需在页面上添加一个 using 'whatevernamespaceyouused' 就可以了。