Question

我有两张桌子

EmpInf
    EmpId,
    EmpName,
    Salary,
    DepartNumber.

Dept
    DeptNo,
    Deptname,

我还有listview1和dropdownlist1绑定到EmpInf.EmpName

传递特定查询时

FilterControl.DataClasses1DataContext obj = new DataClasses1DataContext();
protected void DropDownList1_SelectedIndexChanged1(object sender, EventArgs e)
{
    var a = from r in obj.EmpInfs join s in obj.Dept1s on r.DeptNumber equals s.DeptNo where r.EmpName == "'" + DropDownList1.SelectedValue + "'" select s;

    ListView1.DataSource = a;
    ListView1.DataBind();   
}

每当我从下拉列表中选择一个特定名称时，它都会返回没有返回任何数据。我缺少哪些特定代码或者是否有其他错误？

Answer 1

在SelectedIndexChanged1中放置一个断点并查看SelectedValue的值，以确保DropDownList1.SelectedValue具有员工姓名。您也可以尝试DropDownList1.SelectedText。

string selected = DropDownList1.SelectedValue.ToString();

// e = employee | d = department
var query =
            from   e in obj.EmpInfs
            join   d in obj.Dept1s on e.DeptNumber equals d.DeptNo
            where  e.EmpName == "'" + DropDownList1.SelectedValue + "'"
            select d;

更改此行：

where  e.EmpName == "'" + DropDownList1.SelectedValue + "'"

到这一个：

where  e.EmpName == selected

好的，我在这里的最后一次尝试......在数据绑定之前执行此操作：

ListView1.DataSource = query.ToList();

Answer 2

此处的问题很可能是您在Where子句中添加了搜索条件的单引号：

var a = from r in obj.EmpInfs 
        join s in obj.Dept1s on r.DeptNumber equals s.DeptNo 
        where r.EmpName == "'" + DropDownList1.SelectedValue + "'" 
        select s;

假设DropDownList1.SelectedValue是“Smith”，那么你生成的sql将沿着以下几行：

SELECT *
FROM <tables>
WHERE EmpName = ''Smith''

注意双单引号。要仔细检查这一点，请在生成查询后设置断点，然后在其上调用.ToString（）以获取等效的TSQL。要解决此问题，请从LINQ查询中删除“'”，因为它将自动添加到字符串参数中：

var a = from r in obj.EmpInfs 
        join s in obj.Dept1s on r.DeptNumber equals s.DeptNo 
        where r.EmpName == DropDownList1.SelectedValue 
        select s;

linq to sql：linq查询问题

2 个答案: