*要解決的問題
需求總是改變,有的甚至不能叫需求,一個小小的請求:幫我加個"用戶名"的查詢條件吧,我想有"注冊時間"范圍查詢,"三圍"可以有嗎?
我們需要一個簡單,好用,強大的后台,那么這些可以有,應該有!
*怎么解決
因為一個小小請求的修改,都要修改cs程序,重新編譯發布的項目,不是一個好項目,特別是一個大點的項目
,發布會出現版本問題,而請求人員希望問題馬上可以得到解決,那么解決的方法就顯而易見了:
只修改模板,滿足查詢,驗證等問題:
關於模板里實現驗證的方法請查看我的上篇博文ASP.NET MVC 3.0前后台統一驗證類UniValidate,附源碼
關於模板里實現動態查詢,現在開始介紹:
我們要現實的功能很簡單:通過增加表單控件就可以加入新的查詢條件
類似的頁面如下
*開始實現
我要實現一個直接接受form,生成動態查詢的ef擴展
/// <summary>通過頁面控件動態構建查詢</summary>
public static IQueryable<TSource> WhereDynamic<TSource>(this IQueryable<TSource> source,
NameValueCollection nameValues) where TSource : class
重載擴展
public static IQueryable<TSource> WhereDynamic<TSource>(this IQueryable<TSource> source,
HttpRequestBase request) where TSource : class
{
return WhereDynamic(source, new NameValueCollection { request.QueryString, request.Form });
}
從這個方法出發,思路就很簡單了,就是取得form里的值,動態構建表達式樹,有的同學會有疑問,為什么不用對象做為參數
- 因為form的控件名字部分需要有查詢關系的標注,名字與model名字不一致,這樣要得到對象,要重寫ModelBinder
- 表達樹已經有了類型檢查, ModelBinder也有,有重復,而且加大了復雜性.
生成表達樹的代碼
/// <summary>通過頁面控件動態構建查詢</summary>
public static IQueryable<TSource> WhereDynamic<TSource>(this IQueryable<TSource> source,
NameValueCollection nameValues) where TSource : class
{
if (nameValues.Count > 0)
{
//構建 c=>Body中的c
ParameterExpression param = Expression.Parameter(typeof(TSource), "c");
//構建c=>Body中的Body
var body = GetExpressoinBody(param, nameValues);
if (body != null)
{
//將二者拼為c=>Body
var expression = Expression.Lambda<Func<TSource, bool>>(body, param);
//傳到Where中當做參數，類型為Expression<Func<T,bool>>
return source.Where(expression);
}
}
return source;
}
/// <summary>構建body</summary>
private static Expression GetExpressoinBody(ParameterExpression param, NameValueCollection nameValues)
{
var list = new List<Expression>();
if (nameValues.Count > 0)
{
var plist = param.Type.GetRuntimeProperties().ToDictionary(z => z.Name);//可以加緩存改善性能
foreach (var item in nameValues.AllKeys)
if (item.EndsWith(">"))//可能大小查詢
{
string key = item.TrimEnd('>');
if (!plist.ContainsKey(key) || nameValues[item].Length <= 0) continue;
var rType = plist[key].GetMethod.ReturnType;
if (rType == typeof(string)) continue;
var e1 = Expression.Property(param, key);
object dValue;
if (TryParser(nameValues[item], rType, out dValue))
list.Add(Expression.GreaterThan(e1, Expression.Constant(dValue)));
}
else if (item.EndsWith("<"))//可能大小查詢
{
string key = item.TrimEnd('<');
if (!plist.ContainsKey(key) || nameValues[item].Length <= 0) continue;
var rType = plist[key].GetMethod.ReturnType;
if (rType == typeof(string)) continue;
var e1 = Expression.Property(param, key);
object dValue;
if (TryParser(nameValues[item], rType, out dValue))
{
if (rType == typeof(DateTime)) dValue = ((DateTime)dValue).AddDays(1);
list.Add(Expression.LessThan(e1, Expression.Constant(dValue)));
}
}
else if (plist.ContainsKey(item) && nameValues[item].Length > 0)
{
var e1 = Expression.Property(param, item);
var rType = plist[item].GetMethod.ReturnType;
if (rType == typeof(string))//可能是like查詢
{
var value = nameValues[item].Trim('%');
var e2 = Expression.Constant(value);
if (nameValues[item].Length - value.Length >= 2)
list.Add(Expression.Call(e1, "Contains", null, new Expression[] { e2 }));
else if (nameValues[item].StartsWith("%"))
list.Add(Expression.Call(e1, "EndsWith", null, new Expression[] { e2 }));
else if (nameValues[item].EndsWith("%"))
list.Add(Expression.Call(e1, "StartsWith", null, new Expression[] { e2 }));
else
list.Add(Expression.Equal(e1, e2));
}
else if (nameValues[item].IndexOf(",") > 0)//可能是in查詢
{
if (rType == typeof(short))
{
var searchList = TryParser<short>(nameValues[item]);
if (searchList.Any())
list.Add(Expression.Call(Expression.Constant(searchList), "Contains", null, new Expression[] { e1 }));
}
else if (rType == typeof(int))
{
var searchList = TryParser<int>(nameValues[item]);
if (searchList.Any())
list.Add(Expression.Call(Expression.Constant(searchList), "Contains", null, new Expression[] { e1 }));
}
else if (rType == typeof(long))
{
var searchList = TryParser<long>(nameValues[item]);
if (searchList.Any())
list.Add(Expression.Call(Expression.Constant(searchList), "Contains", null, new Expression[] { e1 }));
}
}
else
{
object dValue;
if (TryParser(nameValues[item], rType, out dValue))
list.Add(Expression.Equal(e1, Expression.Constant(dValue)));
}
}
}
return list.Count > 0 ? list.Aggregate(Expression.AndAlso) : null;
}
只處理大於,小於,in,like,等於的操作,其他的可以自己添加,因為大於小於可能為同一個字段,所以查詢關系標注在了名稱里了
*其他函數,用於類型轉換
private static List<T> TryParser<T>(string value)
{
string[] searchArray = value.Split(',');
List<T> dList = new List<T>();
foreach (var l in searchArray)
{
try
{
T dValue = (T)Convert.ChangeType(l, typeof(T));
dList.Add(dValue);
}
catch { }
}
return dList;
}
private static bool TryParser(string value, Type outType, out object dValue)
{
try
{
dValue = Convert.ChangeType(value, outType);
return true;
}
catch
{
dValue = null;
return false;
}
}
*動態處理分頁
public static IQueryable<TSource> Page<TSource>(this IQueryable<TSource> source, DataPage dp) where TSource : class
{
dp.RowCount = source.Count();
Type type = typeof(TSource);
ParameterExpression param = Expression.Parameter(type, "c");
string callMethod = "OrderByDescending";
PropertyInfo property;
if (dp.OrderField == null)
property = type.GetRuntimeProperties().First();
else
{
//處理正反排序
string[] orderFileds = dp.OrderField.Split(' ');
if (orderFileds.Length == 2)
{
dp.OrderField = orderFileds[0].Trim();
if (String.Compare(orderFileds[1].Trim(), "asc", StringComparison.OrdinalIgnoreCase) == 0) callMethod = "OrderBy";
}
property = type.GetProperty(dp.OrderField) ?? type.GetRuntimeProperties().First();
}
LambdaExpression le = Expression.Lambda(Expression.MakeMemberAccess(param, property), param);
MethodCallExpression resultExp = Expression.Call(typeof(Queryable), callMethod, new[] { type, property.PropertyType }
, source.Expression, Expression.Quote(le));
return source.Provider.CreateQuery<TSource>(resultExp).Skip((dp.PageIndex - 1) * dp.PageSize).Take(dp.PageSize);
}
*如何使用,主要體現在表單里
名字<input name="username" type="text" style="width: 40px" />正常的查詢,如果值里有%號處理成like查詢
ID<input name="id" type="text" value="62" style="width: 30px" /><input name="id" type="text" value="63" style="width: 30px" /> in查詢
時<input name="addtime>" type="text" value="" style="width: 80px" /><input name="addtime<" type="text" value="" style="width: 80px" /> 大於小於查詢
Controller里的調用
public PartialViewResult WherePage(DataPage dp)
{
dp.PageSize = 10;
var tempList = _dbEntities.act_comment.WhereDynamic(Request).Page(dp);
ViewBag.sql = tempList.ToString();
return View(tempList.ToList());
}
Ef擴展的好處是查詢條件可以串接,如上例可以再加查詢條件
var tempList = _dbEntities.act_comment.WhereDynamic(Request).Where(z=>z.forid==1).Page(dp);
*其他
參考了重典 http://www.cnblogs.com/chsword/archive/2010/12/27/searchmodel_1.html ,原理相同,里面有的,我這都沒有細說,比如比拼接sql的優點,
關於表達式樹可以學習腦袋的: http://www.cnblogs.com/Ninputer/archive/2009/08/28/expression_tree1.html
代碼是從老項目copy出來的,沒有單獨的項目,看需要,如果有必要,可以考慮整理一份源碼,代碼上面都有.