linq to sql的多條件動態查詢

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 + "&nbsp;" + item.F_Money.ToString() +  "<br/>");
            }
        }     
    }
//得到合同金額大於6000,或合同名稱中包含"江華"字的條件
    private bool GetCondition(T_Bargin _Table)
    {       

        bool _result = false;

        decimal _MinMoney = 6000;

        if (_MinMoney > 0)
        {
            _result |= _Table.F_Money >= _MinMoney;
        }

        string _Name = "江華";

        if (!String.IsNullOrEmpty(_Name))
        {
            _result |= _Table.F_Name.Contains(_Name);
        }
        
        return _result;
    }

 藉助老外寫的一個擴充套件表示式的類，可以把上篇中的程式碼寫得更優雅

這是PredicateBuilder的原始檔

 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));
        }
        //翻譯後的sql語句:
        //SELECT [t0].[ID], [t0].[Name], [t0].[Description]
        //FROM [dbo].[Product] AS [t0]
        //WHERE ([t0].[Description] LIKE '%手機%') 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);
        //翻譯後的sql語句:
        //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 = "長虹";
        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();
        }

    }

 來自：http://www.cnblogs.com/fireplume/archive/2008/04/27/1172683.html