linq to sql 多條件組合查詢
阿新 • • 發佈:2019-02-02
//一個條件一個條件串接 using System.Linq.Expressions; Expression<Func> exps = A => true; if (GroupId != "0") { Expression<Func> e2 = A => A.GroupId == GroupId[0]; var invokedExpr = Expression.Invoke(e2, exps.Parameters.Cast()); exps = Expression.Lambda<Func>(Expression.And(exps.Body, invokedExpr), exps.Parameters); } if (TypeId != "0") { Expression<Func> e2 = A => A.TypeId == TypeId[0]; var invokedExpr = Expression.Invoke(e2, exps.Parameters.Cast()); exps = Expression.Lambda<Func>(Expression.And(exps.Body, invokedExpr), exps.Parameters); } ....................... //多欄位排序,要使用ThenBy 或 ThenByDescending var AList = ctx.ArticleList.Where(exps).OrderBy(A => A.GroupId).ThenBy(A => A.ArticleTypeId).ThenBy(A => A.AId); //================================================================ //一個老外寫的擴充Expression方法的靜態類別,可以解決上面冗長的程式碼 using System.Linq.Expressions; // /// LinqExpressions 的摘要描述 /// public static class DynamicLinqExpressions//注意static靜態型別 { public static Expression<Func> True() { return f => true; } public static Expression<Func> False() { return f => false; } //注意this public static Expression<Func> Or(this Expression<Func> expr1,Expression<Func> expr2) { var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast()); return Expression.Lambda<Func>(Expression.Or(expr1.Body, invokedExpr), expr1.Parameters); } public static Expression<Func> And(this Expression<Func> expr1,Expression<Func> expr2) { var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast()); return Expression.Lambda<Func>(Expression.And(expr1.Body, invokedExpr), expr1.Parameters); } } //============================================================== //使用範例 using System.Linq.Expressions; ReadPlantDataContext ctx = new ReadPlantDataContext(); var eps = DynamicLinqExpressions.True(); if (this._GroupId != "0") eps = eps.And(A => A.GroupId == this._GroupId[0]); if (this._TypeId != "0") eps = eps.And(A => A.ArticleTypeId == this._TypeId[0]); if (this._IsAllow != "0") eps = eps.And(A => A.Checked == Convert.ToBoolean(this._IsAllow)); if (this._IsCommend != "0") eps = eps.And(A => A.IsCommend == Convert.ToBoolean(this._IsCommend)); if (this._StartDate != DateTime.MinValue) eps = eps.And(A => A.AddDate >= this._StartDate); if (this._EndDate != DateTime.MinValue) eps = eps.And(A => A.AddDate <= this._EndDate); //多欄位排序,要使用ThenBy 或 ThenByDescending var AList = ctx.ArticleList.Where(eps).OrderBy(A => A.GroupId).ThenBy(A => A.ArticleTypeId).ThenBy(A => A.AId); Expression.invoke 參考:http://msdn.microsoft.com/en-us/library/bb355170.aspx Lambda Expressions 參考:http://msdn.microsoft.com/en-us/library/bb397687.aspx Expression.Lambda 參考:http://dszhang.blog.163.com/blog/static/12281257420106910952813/