使用实体框架对 Gridview 进行排序。

Question

我有办法

private void BindGrid()
{
    dataContext = new VTCEntities();
    string SortExpression = "DisplayName";
    string SortDirection = "ASC";
    int skip = 0;

    if (this.ViewState["SortExp"] != null)
    {
        SortExpression = this.ViewState["SortExp"].ToString();
    }

    if (this.ViewState["SortOrder"] != null)
    {
        string d = this.ViewState["SortOrder"].ToString();
        if (d == "ASC")
        {
            SortDirection = "ASC";
        }
        else
        {
            SortDirection = "DESC";
        }
    }

    if (CurrentPage != 0)
    {
        skip = CurrentPage * PageSize;
    }

    if (SortDirection == "ASC")
    {
        this.grdCustomers.DataSource = dataContext.CustomerSet.OrderBy(i => i.DisplayName).Skip(skip).Take(PageSize);
    }
    else
    {
        this.grdCustomers.DataSource = dataContext.CustomerSet.OrderByDescending(i => i.DisplayName).Skip(skip).Take(PageSize);
    }

    this.grdCustomers.DataBind();
}

它开始闻起来了，不好。我有 4 列需要排序。我想避免进行切换或其他操作来确定我要订购的 CustomerSet 上的哪个属性。一个更好的程序员如何将 SortExpression（一个字符串）关联到我的 CustomerSet 对象之一的属性？

一如既往的感谢。
吉姆

Answer 1

我过去曾为此使用过这种扩展方法：

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);
    }
}

来源：http://weblogs.asp.net/davidfowler/archive/2008/12/11/dynamic-sorting-with-linq.aspx

然后你可以重写这个：

        if (SortDirection == "ASC")
        {
            this.grdCustomers.DataSource = dataContext.CustomerSet.OrderBy(i => i.DisplayName).Skip(skip).Take(PageSize);
        }
        else
        {
            this.grdCustomers.DataSource = dataContext.CustomerSet.OrderByDescending(i => i.DisplayName).Skip(skip).Take(PageSize);
        }

到

this.grdCustomers.DataSource = dataContext.CustomerSet.SortBy("DisplayName DESC").Skip(skip).Take(PageSize);