void ShowData() { using (DBDataContext db = new DBDataContext(Database.ConnectionString)) { Expression<Func<T_Bargin, bool>> expr = n => GetCondition(n); var _query = db.T_Bargins.Where<T_Bargin>(expr.Compile()).Select(b => new { b.F_Money, b.F_Name }); foreach (var item in _query) { Response.Write(item.F_Name + " " + item.F_Money.ToString() + "<br/>"); } } } //得到合同金额大于6000,或合同名称中包含"江华"字的条件 private bool GetCondition(T_Bargin _Table) { bool _result = false; decimal _MinMoney = 6000; if (_MinMoney > 0) { _result |= _Table.F_Money >= _MinMoney; } string _Name = "江华"; if (!String.IsNullOrEmpty(_Name)) { _result |= _Table.F_Name.Contains(_Name); } return _result; } 借助老外写的一个扩展表达式的类，可以把上篇中的代码写得更优雅
这是PredicateBuilder的源文件
public static class PredicateBuilder { public static Expression<Func<T, bool>> True<T> () { return f => true; } public static Expression<Func<T, bool>> False<T> () { return f => false; } 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); } }
下面是使用示例 ：
List<Product> GetProductsByAND(params string[] keywords) { DBDataContext db = new DBDataContext(Database.ConnectionString); IQueryable<Product> query = db.Products; foreach (string keyword in keywords) { string temp = keyword; query = query.Where(p => p.Description.Contains(keyword)); } //翻译后的sql语句: //SELECT [t0].[ID], [t0].[Name], [t0].[Description] //FROM [dbo].[Product] AS [t0] //WHERE ([t0].[Description] LIKE '%手机%') AND ([t0].[Description] LIKE '%6111%') return query.ToList(); } List<Product> GetProductsByOR(params string[] keywords) { DBDataContext db = new DBDataContext(Database.ConnectionString); var predicate = PredicateBuilder.False<Product>(); foreach (string keyword in keywords) { string temp = keyword; predicate = predicate.Or(p => p.Description.Contains(temp)); } var query = db.Products.Where(predicate); //翻译后的sql语句: //SELECT [t0].[ID], [t0].[Name], [t0].[Description] //FROM [dbo].[Product] AS [t0] //WHERE ([t0].[Description] LIKE '%6111%') OR ([t0].[Description] LIKE '%2350%') return query.ToList(); } void ShowData() { //var _products = GetProductsByOR("6111", "2350"); //Repeater1.DataSource = _products; //Repeater1.DataBind(); var predicate = PredicateBuilder.True<Product>(); string _name = "6111"; if (!string.IsNullOrEmpty(_name)) { predicate = predicate.And(p => p.Name.Contains(_name)); } string _description = "长虹"; if (!string.IsNullOrEmpty(_description)) { predicate = predicate.And(p => p.Description.Contains(_description)); } using (DBDataContext db = new DBDataContext(Database.ConnectionString)) { var _Products = db.Products.Where(predicate); Repeater1.DataSource = _Products; Repeater1.DataBind(); } } 来自： http://www.cnblogs.com/fireplume/archive/2008/04/27/1172683.html
