前言
搜尋功能是一個很常用的功能，當然這個搜尋不是指全文檢索索引，是指網站的後台管理系統或ERP系統列表的搜尋功能。常見做法一般就是在搜尋欄上加上幾個常用欄位來搜尋。代碼可能一般這樣實現
StringBuilder sqlStr = new StringBuilder();if (!string.IsNullOrEmpty(RealName)){ sqlStr.Append(" and RealName = @RealName");}if (Age != -1){ sqlStr.Append(" and Age = @Age");}if (!string.IsNullOrEmpty(StartTime)){ sqlStr.Append(" and CreateTime >= @StartTime");}if (!string.IsNullOrEmpty(EndTime)){ sqlStr.Append(" and CreateTime <= @EndTime");}MySqlParameter[] paras = new MySqlParameter[]{ new MySqlParameter("@Age", Age), new MySqlParameter("@RealName", RealName), new MySqlParameter("@StartTime", StartTime), new MySqlParameter("@EndTime", EndTime) };
這段代碼如果遇到下面幾個需求，又該如何處理？
再加一個查詢欄位
RealName需要改成模糊查詢
Age需要支援範圍查詢
可能大多數程式猿想法，這是新的需求，那麼就直接改代碼，簡單粗暴。然後在前台加個age範圍文字框，後台再加個if判斷，realname的=號就直接改成like，就這樣輕鬆搞定了。但需求總是不斷變化，如果一張表有50個欄位，同時需要支援其中40個欄位查詢。我想大都數人第一反應：臥槽，神經病！難道就沒有一個通用的辦法來解決這種搜尋的問題？我想說當然有，本文接下來就用DapperExtensions和反射的來解決這個問題，最終於實現的效果如：
DapperExtensions介紹
DapperExtensions是基於Dapper的一個擴充，主要在Dapper基礎上實現了CRUD的操作。它還提供了一個謂詞系統，可以實現更多複雜的進階查詢功能。還可以通過ClassMapper來定義實體類和表的映射。
通用搜尋功能實現
1.首先建立一個account表，然後增加一個Account類
public class Account { public Account() { Age = -1; } /// <summary> /// 賬戶ID /// </summary> [Mark("賬戶ID")] public int AccountId { get; set; } /// <summary> /// 姓名 /// </summary> [Mark("姓名")] public string RealName { get; set; } /// <summary> /// 年齡 /// </summary> [Mark("年齡")] public int Age { get; set; } /// <summary> /// 建立時間 /// </summary> [Mark("建立時間")] public DateTime CreateTime { get; set; } }
2.為了擷取欄位對應的中文名稱，我們增加一個MarkAttribute類。因為有強大的反射功能，我們可以通過反射動態擷取每張表實體類的屬性和中文名稱。
[AttributeUsage(AttributeTargets.Property, Inherited = false, AllowMultiple = true)] public class MarkAttribute : Attribute { public MarkAttribute(string FiledName, string Description = "") { this.FiledName = FiledName; this.Description = Description; } private string _FiledName; public string FiledName { get { return _FiledName; } set { _FiledName = value; } } private string _Description; public string Description { get { return _Description; } set { _Description = value; } } }
3.通用搜尋思路主要是把搜尋功能抽象出一個對象，本質上也就列名、操作符、值組成的一個對象集合，這樣就可以實現多個搜尋條件的組合。我們增加一個Predicate類
public class Predicate { /// <summary> /// 列名 /// </summary> public string ColumnItem { get; set; } /// <summary> /// 操作符 /// </summary> public string OperatorItem { get; set; } /// <summary> /// 值 /// </summary> public object Value { get; set; } }
4.然後通過反射Account類的屬性載入到前台列名的DropDownList，再增加一個操作符的DropDownList
var columnItems = new List<SelectListItem>(); //通過反射來擷取類的屬性 Type t = Assembly.Load("SearchDemo").GetType("SearchDemo.Models.Account"); foreach (PropertyInfo item in t.GetProperties()) { string filedName = (item.GetCustomAttributes(typeof(MarkAttribute), false)[0] as MarkAttribute).FiledName; columnItems.Add(new SelectListItem() { Text = filedName, Value = item.Name }); } ViewBag.columnItems = columnItems; var operatorItems = new List<SelectListItem>() { new SelectListItem() {Text = "等於", Value = "Eq"}, new SelectListItem() {Text = "大於", Value = "Gt"}, new SelectListItem() {Text = "大於或等於", Value = "Ge"}, new SelectListItem() {Text = "小於", Value = "Lt"}, new SelectListItem() {Text = "小於或等於", Value = "Le"}, new SelectListItem() {Text = "模糊", Value = "Like"} }; ViewBag.operatorItems = operatorItems;
5.前台介面實現代碼
<!DOCTYPE html><html><head> <title>DapperExtensions通用搜尋</title> <script src="../../scripts/jquery-1.4.4.min.js" type="text/javascript"></script> <script type="text/javascript"> Date.prototype.format = function (format) { var o = { "M+": this.getMonth() + 1, //month "d+": this.getDate(), //day "h+": this.getHours(), //hour "m+": this.getMinutes(), //minute "s+": this.getSeconds(), //second "q+": Math.floor((this.getMonth() + 3) / 3), //quarter "S": this.getMilliseconds() //millisecond } if (/(y+)/.test(format)) { format = format.replace(RegExp.$1, (this.getFullYear() + "").substr(4 - RegExp.$1.length)); } for (var k in o) { if (new RegExp("(" + k + ")").test(format)) { format = format.replace(RegExp.$1, RegExp.$1.length == 1 ? o[k] : ("00" + o[k]).substr(("" + o[k]).length)); } } return format; } </script> <style type="text/css"> ul { list-style: none; padding: 0px; margin: 0px; width: 590px; height: 20px; line-height: 20px; border: 1px solid #99CC00; border-top: 0px; font-size: 12px; } ul li { display: block; width: 25%; float: left; text-indent: 2em; } .th { background: #F1FADE; font-weight: bold; border-top: 1px solid #99CC00; } </style> <script type="text/javascript"> var predicates = []; var index = 0; $(document).ready(function () { $("#btnAdd").click(function () { var columnItem = $("#columnItems option:selected"); var operatorItem = $("#operatorItems option:selected"); var value = $("#value").val(); if(value == ""){ alert("請輸入值"); return; } var predicate = { index: index, columnItem: columnItem.val(), operatorItem: operatorItem.val(), value: value }; predicates.push(predicate); var html = "<ul><li>" + columnItem.text() + "</li><li>" + operatorItem.text() + "</li><li>" + value + "</li><li><a href='javascript:;' onclick='del(this," + index + ")'>刪除</a></li></ul>" $("#predicates ul:last").after(html); index++; }) $("#btnSearch").click(function () { $.ajax({ type: "POST", url: "home/search", data: JSON.stringify(predicates), contentType: "application/json", success: function (data) { if (data.Error != null) { alert(data.Error); return; } $("#list .th").nextAll().remove(); var html = ""; $.each(data, function (index, item) { html += "<ul><li>" + item.AccountId + "</li>"; html += "<li>" + item.RealName + "</li>"; html += "<li>" + item.Age + "</li>"; //轉換日期 var dateMilliseconds = parseInt(item.CreateTime.replace(/\D/igm, "")); var date = new Date(dateMilliseconds); html += "<li>" + date.format("yyyy-MM-dd hh:mm:ss") + "</li></ul>"; }); $("#list .th").after(html); } }); }) }) function del(obj,index) { obj.parentNode.parentNode.remove(); for (var i = 0; i < predicates.length; i++) { if (predicates[i].index == index) { predicates.splice(i, 1); } } } </script></head><body> <p> 列名：@Html.DropDownList("columnItems") 操作符：@Html.DropDownList("operatorItems") 值：@Html.TextBox("value") <input id="btnAdd" type="button" value="增加" /> <input id="btnSearch" type="button" value="搜尋" /> </p> <br /> <p id="predicates"> <ul class="th"> <li>列名</li> <li>操作符</li> <li>值</li> <li>操作</li> </ul> </p> <br /> <p id="list"> <ul class="th"> <li>賬戶ID</li> <li>姓名</li> <li>年齡</li> <li>建立時間</li> </ul> </p></body></html>
6.最後通過DapperExtensions的謂詞和反射實現搜尋方法
[HttpPost] public JsonResult Search(List<Predicate> predicates) { if (predicates == null) { return Json(new { Error = "請增加搜尋條件" }); } using (var connection = SqlHelper.GetConnection()) { var pga = new PredicateGroup { Operator = GroupOperator.And, Predicates = new List<IPredicate>() }; foreach (var p in predicates) { var predicate = Predicates.Field<Account>(GetExpression(p), (Operator)Enum.Parse(typeof(Operator), p.OperatorItem), p.Value); pga.Predicates.Add(predicate); } var list = connection.GetList<Account>(pga); return Json(list); } } private static Expression<Func<Account, object>> GetExpression(Predicate p) { ParameterExpression parameter = Expression.Parameter(typeof(Account), "p"); return Expression.Lambda<Func<Account, object>>(Expression.Convert(Expression.Property(parameter, p.ColumnItem), typeof(object)), parameter); }
最終，通過簡單的幾行代碼，在基於DapperExtensions的功能基礎上，我們最終實現了一個可以支援多個欄位、多個條件、多個操作符的通用查詢功能。本文也只是拋磚引玉，只是提供一種思路，還有更多細節沒有考慮。比如多個條件的組合可以再增加一個邏輯符來串連、多個條件組合巢狀查詢、多表查詢等等。
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