我使用此方法在Blazor Serverside中检索Tree组件的项目,在DAL中,我有:
public List<TreeItem> GetTreeItems()
{
var tree = new List<TreeItem>();
TreeItem item = new TreeItem()
{
DepartmentID = 0,
CategoryID = 0,
Text = "Root",
Childs = context.Departments.OrderBy(d => d.Order).Select(d => new TreeItem()
{
DepartmentID = d.Id,
CategoryID = 0,
Text = d.Title,
Childs = d.Categories.OrderBy(c => c.Order).Select(c => new TreeItem()
{
DepartmentID = d.Id,
CategoryID = c.Id,
Text = c.Title
}).ToList()
}).ToList()
};
tree.Add(item);
return tree;
}
TreeItem类如下(blazor Component和Dal类共享的模型):
public class TreeItem
{
public int DepartmentID { get; set; }
public int CategoryID { get; set; }
public string Text { get; set; }
public List<TreeItem> Childs { get; set; }
}
但是,当我在blazor组件中检索树的Items时,会得到一个例外:由于对象的当前状态,操作无效。,admin是我向Blazor组件注入的DAL类,如下所示:
private void GetTreeModel()
{
try
{
Items = admin.GetTreeItems();
TreeSuccess = true;
TreeMessage = "Success";
return;
}
catch (Exception ex) // Error here
{
TreeSuccess = false;
TreeMessage = "Can not load tree items";
return;
}
}
这是什么错误以及如何解决?
我首先使用加载实体,然后对对象使用Linq来解决问题,如下所示:
var tree = new List<TreeItem>();
var departments = context.Departments.OrderBy(d => d.Order).ToList();
var categories = context.Categories.OrderBy(c => c.Order).ToList();
TreeItem item = new TreeItem()
{
DepartmentID = 0,
CategoryID = 0,
Text = "Root",
Childs = departments.Select(d => new TreeItem()
{
DepartmentID = d.Id,
CategoryID = 0,
Text = d.Title,
Childs = categories.Where(c => c.DepartmentID == d.Id).OrderBy(c => c.Order).Select(c => new TreeItem()
{
DepartmentID = d.Id,
CategoryID = c.Id,
Text = c.Title
}).ToList()
}).ToList()
};
tree.Add(item);
return tree;
}
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