AppBox升級進行時 - 如何向OrderBy傳遞字符串參數（Entity Framework）

時間 2019-11-25

標籤 appbox 升級進行如何 orderby 傳遞字符串參數 entity framework 欄目 SQL 简体版

原文原文鏈接

AppBox 是基於 FineUI 的通用權限管理框架，包括用戶管理、職稱管理、部門管理、角色管理、角色權限管理等模塊。php

Entity Framework提供的排序功能

再來回顧一下上篇文章，加載用戶列表並進行排序數據庫分頁的代碼：數據庫

var q = DB.Users.Include(u => u.Dept);
 
// 在用戶名稱中搜索
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));
}
 
// 過濾啓用狀態
if (rblEnableStatus.SelectedValue != "all")
{
    q = q.Where(u => u.Enabled == (rblEnableStatus.SelectedValue == "enabled" ? true : false));
}
 
// 在查詢添加以後，排序和分頁以前獲取總記錄數
Grid1.RecordCount = q.Count();
 
// 排列
q = q.OrderBy(u => u.Name);
 
// 數據庫分頁
q = q.Skip(Grid1.PageIndex * Grid1.PageSize).Take(Grid1.PageSize);
 
Grid1.DataSource = q;
Grid1.DataBind();

讓咱們把關注點集中到排序代碼上：框架

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

在FineUI實際應用中，咱們通常是從表格的 SortField 中讀取排序字段，顯然EF提供的OrderBy沒法接受字符串表示的排序字段。ide

手工建立Lamba表達式　　

經過搜索發現了這個帖子：http://stackoverflow.com/questions/10072250/generic-funct-k-to-sort-collections-of-different-types/10074873函數

據此咱們能夠寫出以下的代碼：測試

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;
}

通過測試，咱們發現這個方法不支持bool, int, DateTime, DateTime?類型的列排序。優化

通過擴展後的代碼以下所示：ui

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;
}

但這種作法過於臃腫，有沒有更好的辦法呢？this

更好的SortBy擴展方法　　

後來，咱們發現了這篇文章：http://stackoverflow.com/questions/3945645/sorting-gridview-with-entity-frameworkspa

經過對 IQueryable<T> 進行擴展，提供了接受相似 "Name DESC", "CreateTime", "CreateTime DESC" 參數的 SortBy 方法，更具備通用性。

原始的SortBy擴展方法：

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);
    }
}

不過這個方法不支持"Name ASC"形式的參數，因此咱們進行了簡單的修正，修正後的SortBy擴展方法：

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);
    }
 
}

優化後的排序分頁代碼

首先在頁面基類PageBase中定義排序和分頁的代碼（使用了前面定義的 SortBy 擴展函數）：

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);
}

最終查詢用戶列表的代碼：

var q = DB.Users.Include(u => u.Dept);
 
// 在用戶名稱中搜索
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));
}
 
// 過濾啓用狀態
if (rblEnableStatus.SelectedValue != "all")
{
    q = q.Where(u => u.Enabled == (rblEnableStatus.SelectedValue == "enabled" ? true : false));
}
 
// 在查詢添加以後，排序和分頁以前獲取總記錄數
Grid1.RecordCount = q.Count();
 
// 排列和數據庫分頁
q = SortAndPage<User>(q, Grid1);
 
 
Grid1.DataSource = q;
Grid1.DataBind();