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(temp)); } //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(); } }
