C#-WebForm-组合查询（Queryable延迟查询、Intersect交集）、分页展示基础

组合查询：

方法一：Queryable<> 延迟查询

其特点是：读到词句代码时不会立即执行，而是在进行数据绑定时执行

优点：此期间可以进行添加查询条件，以减少数据库查询内容，来减少内存占用量

//<查询>按钮
    void btn_select_Click(object sender, EventArgs e)
    {
        using (CarDataContext con = new CarDataContext())
        {
            //进行查询，将查询到的数据放入Queryable集合中
            IQueryable<Car> clist = con.Car.AsQueryable();
            //其特点是：读到词句代码时不会立即执行，而是在进行数据绑定时执行
            //优点：此期间可以进行添加查询条件，以减少数据库查询内容，来减少内存占用量

            //对每一个条件文本框进行判断，是否有限制条件
            string name = txt_name.Text.Trim();
            string brand = txt_brand.Text.Trim();
            string price = txt_price.Text.Trim();

            if (name.Length > )
            {
                //如果有限制条件则添加查询条件
                clist = clist.Where(r => r.Name.Contains(name.Trim()));
            }

            if (brand.Length > )
            {
                clist = clist.Where(r => r.Brand.Contains(brand.Trim()));
            }

            if (price.Length > )
            {
                string s = DropDownList1.SelectedValue;
                if (s == "=")
                    clist = clist.Where(r => r.Price == Convert.ToDecimal(price));
                if (s == ">=")
                    clist = clist.Where(r => r.Price >= Convert.ToDecimal(price));
                if (s == "<=")
                    clist = clist.Where(r => r.Price <= Convert.ToDecimal(price));
            }

            //绑定数据-此时Queryable进行数据库查询并绑定数据
            Repeater1.DataSource = clist;
            Repeater1.DataBind();
        }

方法二：Intersect 交集

void Button2_Click(object sender, EventArgs e)
    {
        //先按照查询条件，将所有的数据分别查询全部出来
        using(mydbDataContext con = new mydbDataContext())
        {
            var nameList = con.car.AsQueryable();
            var brandList = con.car.AsQueryable();
            var priceList = con.car.AsQueryable();

            string name = txt_name.Text.Trim();
            string brand = txt_brand.Text.Trim();
            string price = txt_price.Text.Trim();

            if (name.Length > )
            {
                nameList = nameList.Where(r => r.name.Contains(name));
            }
            if (brand.Length > )
            {
                brandList = brandList.Where(r => r.brand.Contains(brand));
            }
            if (price.Length > )
            {
                string aa = DropDownList1.SelectedValue;
                if (aa == "=")
                    priceList = priceList.Where(r => r.price == Convert.ToDecimal(price));
                if (aa == ">=")
                    priceList = priceList.Where(r => r.price >= Convert.ToDecimal(price));
                if (aa == "<=")
                    priceList = priceList.Where(r => r.price <= Convert.ToDecimal(price));
            }

            //取集合的交集
            var allList = nameList.Intersect(brandList).Intersect(priceList);

            Repeater1.DataSource = allList;
            Repeater1.DataBind();

        }
    }

分页展示：

Repeater1.DataSource = clist.Skip(Count1).Take(Count2);

Repeater1.DataBind();

int AllDataCout = clist.Count();

int Count1——跳过多少条数据　　　 int Count2——取多少条数据　　AllDataCout ——查询出来的数据一共多少条