[英]Fill WinForms DataGridView From Anonymous Linq Query
// From my form //来自我的表格
BindingSource bs = new BindingSource();
private void fillStudentGrid()
{
bs.DataSource = Admin.GetStudents();
dgViewStudents.DataSource = bs;
}
// From the Admin class //来自Admin类
public static List<Student> GetStudents()
{
DojoDBDataContext conn = new DojoDBDataContext();
var query =
(from s in conn.Students
select new Student
{
ID = s.ID,
FirstName = s.FirstName,
LastName = s.LastName,
Belt = s.Belt
}).ToList();
return query;
}
I'm trying to fill a datagridview control in Winforms, and I only want a few of the values. 我正在尝试在Winforms中填充datagridview控件,我只想要一些值。 The code compiles, but throws a runtime error:
代码编译,但会引发运行时错误:
Explicit construction of entity type 'DojoManagement.Student' in query is not allowed. 不允许在查询中显式构造实体类型“DojoManagement.Student”。
Is there a way to get it working in this manner? 有没有办法让它以这种方式工作?
You already have an IEnumerable<Student>
instance and you cannot project entities from a query for the reasons described here ) 您已经有一个
IEnumerable<Student>
实例,由于此处描述的原因,您无法从查询中投影实体)
You also don't need to create a list to bind to this data source - you can greatly simplify your method by changing it to this: 您也不需要创建一个列表来绑定到此数据源 - 您可以通过将其更改为此方法来大大简化您的方法:
public static IEnumerable<Student> GetStudents()
{
return new DojoDBDataContext().Students;
}
There is no reason to project a new instance to only map a few of the properties, by executing the query you are returning all the values anyhow and your projection doesn't save you anything. 没有理由将新实例投影到仅映射一些属性,通过执行查询无论如何返回所有值,并且您的投影不会保存任何内容。 If you really want to only return a few values from this query for the purposes of information hiding you could do this:
如果您确实只想从信息隐藏中返回此查询中的一些值,则可以执行以下操作:
public static IEnumerable<Object> GetStudents()
{
DojoDBDataContext conn = new DojoDBDataContext();
return conn.Students
.Select(s => new {
ID = s.ID,
FirstName = s.FirstName,
LastName = s.LastName,
Belt = s.Belt
});
}
Edit: If you aren't using C# 4 you will have to cast the contents of the IEnumerable<T>
to Object
explicitly. 编辑:如果您不使用C#4,则必须明确地将
IEnumerable<T>
的内容IEnumerable<T>
为Object
。 Only C# 4 supports covariance for IEnumerable<T>
. 只有C#4支持
IEnumerable<T>
协方差。 So if you are using C# 3 you will have to do this: 因此,如果您使用的是C#3,则必须执行以下操作:
public static IEnumerable<Object> GetStudents()
{
DojoDBDataContext conn = new DojoDBDataContext();
return conn.Students
.Select(s => new {
ID = s.ID,
FirstName = s.FirstName,
LastName = s.LastName,
Belt = s.Belt
}).Cast<Object>();
}
Once I was looking around for a solution to display results on a Gridview. 一旦我四处寻找在Gridview上显示结果的解决方案。 The problem I had was that I forgot to set property of datagrid : "Data Source" to None on Winform.
我遇到的问题是我忘了在Winform上将datagrid的属性设置为None:“Data Source”。
This is simple solution for display gridview with linq (just sample code) 这是使用linq显示gridview的简单解决方案(只是示例代码)
DataGrid dataGrid1 = new DataGrid();
var custQuery =
from cust in db.Customers
select cust;
dataGrid1.DataSource = custQuery;
Just return a list of objects of an anonymous type : 只需返回匿名类型的对象列表:
public static List<object> GetStudents()
{
DojoDBDataContext conn = new DojoDBDataContext();
var query =
(from s in conn.Students
select new
{
ID = s.ID,
FirstName = s.FirstName,
LastName = s.LastName,
Belt = s.Belt
}).Cast<object>().ToList();
return query;
}
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