linq to sql 多条件组合查询
//一個條件一個條件串接
using System.Linq.Expressions; Expression<Func<ArticleList, bool>> exps = A => true; if (GroupId != "0") { Expression<Func<ArticleList, bool>> e2 = A => A.GroupId == GroupId[0]; var invokedExpr = Expression.Invoke(e2, exps.Parameters.Cast<Expression>()); exps = Expression.Lambda<Func<ArticleList, bool>>(Expression.And(exps.Body, invokedExpr), exps.Parameters); } if (TypeId != "0") { Expression<Func<ArticleList, bool>> e2 = A => A.TypeId == TypeId[0]; var invokedExpr = Expression.Invoke(e2, exps.Parameters.Cast<Expression>()); exps = Expression.Lambda<Func<ArticleList, bool>>(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; // <summary> /// LinqExpressions 的摘要描述 /// </summary> public static class DynamicLinqExpressions//注意static靜態型別 { public static Expression<Func<T, bool>> True<T>() { return f => true; } public static Expression<Func<T, bool>> False<T>() { return f => false; } //注意this public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expr1, Expression<Func<T, bool>> expr2) { var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>()); return Expression.Lambda<Func<T, bool>> (Expression.Or(expr1.Body, invokedExpr), expr1.Parameters); } public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expr1, Expression<Func<T, bool>> expr2) { var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>()); return Expression.Lambda<Func<T, bool>> (Expression.And(expr1.Body, invokedExpr), expr1.Parameters); } } //============================================================== //使用範例 using System.Linq.Expressions; ReadPlantDataContext ctx = new ReadPlantDataContext(); var eps = DynamicLinqExpressions.True<ArticleList>(); 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 参考:http://msdn.microsoft.com/en-us/library/bb355170.aspx Lambda Expressions 参考:http://msdn.microsoft.com/en-us/library/bb397687.aspx
Expression.Lambda 参考:http://dszhang.blog.163.com/blog/static/12281257420106910952813/