Linq 高级查询

Posted 2020-09-21 常啸森

tags:

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以~结尾:

r=>r.Name.EndsWith("光");

包含(模糊查询):

r=>r.Name.Contains("四");

数据总个数:

Con.Goods.Count();||Con.Users.ToList().count;

最大值:

Con.Goods.ToList().Max(r=>r.Price);

最小值:

Con.Goods.ToList().Min(r=>r.Price);

平均值:

Con.Goods.ToList().Average(r=>r.Price);

求和:

Con.Goods.ToList().Sum(r=>r.Price);

升序:

Con.Goods.ToList().OrderBy(r=>r.Price);

降序:

Con.Goods.ToList().OrderByDescending(r=>r.Price);

////////////////////////////////////////////////////////

"T1" runat="server"></asp:TextBox></div> <div> 性别:<asp:DropDownList ID="DropDownList1" runat="server"> <asp:ListItem Text="男和女" Value="Null"></asp:ListItem> <asp:ListItem Text="男" Value="True"></asp:ListItem> <asp:ListItem Text="女" Value="False"></asp:ListItem> </asp:DropDownList> </div> <div> 成绩:<asp:DropDownList ID="DropDownList2" runat="server"> <asp:ListItem Text="不限" Value="Null"></asp:ListItem> <asp:ListItem Text="大于" Value=">"></asp:ListItem> <asp:ListItem Text="小于" Value="<"></asp:ListItem> </asp:DropDownList><asp:TextBox ID="T2" runat="server"></asp:TextBox> </div> <asp:Button ID="Button2" runat="server" Text="查询" />

 void Button2_Click(object sender, EventArgs e)
    {
        using (StudentsDataClassesDataContext con = new StudentsDataClassesDataContext())
        {
            List<Stu> s = con.Stu.ToList();
            if (T1.Text.Trim().Length > 0)
            { s = s.Where(r => r.Name.Contains(T1.Text.Trim())).ToList(); }
            if (DropDownList1.SelectedValue != "Null")
            {  s = s.Where(r => r.Sex == Convert.ToBoolean(DropDownList1.SelectedValue)).ToList();}
            if (DropDownList2.SelectedValue != "Null")
            {
                if (DropDownList2.SelectedValue == ">")
                { s = s.Where(r => r.Score > Convert.ToInt32((T2.Text.Trim()))).ToList(); }
                else
                { s = s.Where(r => r.Score < Convert.ToInt32((T2.Text.Trim()))).ToList(); }
            }
            Repeater1.DataSource = s;
            Repeater1.DataBind();
        }
    }

组合查询+分页查询:

在组合查询和分页查询的时候出现了一个问题,提示XXX已释放,无法调用,问题原因是由于把查询写成了一个方法,在页面加载的时候这个方法没有给属性拓展用上,导致对属性推展部分无法查询,

int Pcount = 2;
    protected void Page_Load(object sender, EventArgs e)
    {

        if (!IsPostBack)
        {//绑定数据,跳过0条,取2条
            using (StudentsDataClassesDataContext con = new StudentsDataClassesDataContext())
            {
                Repeater1.DataSource = SS(con).Take(Pcount);
                Repeater1.DataBind();
                L3.Text = MaxP().ToString();
            }
            //Repeater1.DataSource = con.Stu.ToList();
            //Repeater1.DataBind();
        }

        Button1.Click += Button1_Click;
        Button2.Click += Button2_Click;
        //Button4.Click += Button4_Click;
        //Button5.Click += Button5_Click;
        Button3.Click += Button3_Click;
        Button6.Click += Button6_Click;
    }

    void Button6_Click(object sender, EventArgs e)
    {
        using (StudentsDataClassesDataContext con = new StudentsDataClassesDataContext())
        {
            int a = Convert.ToInt32(L2.Text) + 1;
            if (a > Convert.ToInt32(MaxP()))
            { return; }
            Repeater1.DataSource = SS(con).Skip((a - 1) * Pcount).Take(Pcount);
            Repeater1.DataBind();
            L2.Text = a.ToString();

        }
    }

    void Button3_Click(object sender, EventArgs e)
    {
        using (StudentsDataClassesDataContext con = new StudentsDataClassesDataContext())
        {
            int a = Convert.ToInt32(L2.Text) - 1;
            if (a < 1)
            { return; }
            Repeater1.DataSource = SS(con).Skip((a - 1) * Pcount).Take(Pcount);
            Repeater1.DataBind();
            L2.Text = a.ToString();
        }
    }

    void Button2_Click(object sender, EventArgs e)
    {
        using (StudentsDataClassesDataContext con = new StudentsDataClassesDataContext())
        {
            Repeater1.DataSource = SS(con).Take(Pcount);
            Repeater1.DataBind();
            L2.Text = "1";
            L3.Text = MaxP().ToString();
        }
    }

    //void Button5_Click(object sender, EventArgs e)
    //{
    //    Response.Redirect("toupiao.aspx");
    //}

    //void Button4_Click(object sender, EventArgs e)
    //{
    //    Response.Cookies["id2"].Expires = DateTime.Now.AddDays(-10);
    //}
    //添加
    void Button1_Click(object sender, EventArgs e)
    {
        Response.Redirect("Add.aspx");
    }
    //把组合查询封装成一个方法
    public List<Stu> SS(StudentsDataClassesDataContext con)
    {
        List<Stu> s = con.Stu.ToList();

        if (T1.Text.Trim().Length > 0)
        { s = s.Where(r => r.Name.Contains(T1.Text.Trim())).ToList(); }
        if (DropDownList1.SelectedValue != "Null")
        {
            s = s.Where(r => r.Sex == Convert.ToBoolean(DropDownList1.SelectedValue)).ToList();
        }
        if (DropDownList2.SelectedValue != "Null")
        {
            if (DropDownList2.SelectedValue == ">")
            { s = s.Where(r => r.Score > Convert.ToInt32((T2.Text.Trim()))).ToList(); }
            else
            { s = s.Where(r => r.Score < Convert.ToInt32((T2.Text.Trim()))).ToList(); }
        }
        return s;
    }
    ////获取最大页数
    public int MaxP()
    {
        using (StudentsDataClassesDataContext con = new StudentsDataClassesDataContext())
        {
            return Convert.ToInt32(Math.Ceiling(Convert.ToDecimal(SS(con).Count) / Pcount));
        }
    }

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