Question

所以我正在尝试制作动态报告，我们的用户可以保存并稍后参考。我决定使用linq，并学习更多关于它的内容。我觉得我有很多这个想法，但最后却被困住了。这是我的代码

protected void executeReport(CustomerCustomReports report)
{
    string fields = report.fields;
    ReportsDataContext db = new ReportsDataContext();
    string[]filters = fields.Split(';');

        var inventoryList = (from cust in db.Customers
                             join product in db.Products on cust.customerID equals product.customerID
                             join inventory in db.Inventories on product.itemID equals inventory.ItemId
                             join warehouse in db.Warehouses on inventory.WarehouseId equals warehouse.Id
                             where cust.customerID == customer.CustomerId
                             select new
                             {
                                 ItemID = product.itemID,
                                 ItemDescription = product.shortDesc,
                                 CustomsValue = product.unitPrice
                             }).OrderBy(k => k.ItemID);

ParameterExpression sourceItem = Expression.Parameter(inventoryList.ElementType, "x");

        Type resultType = typeof(linqResult);

        var dynamicFields = new List<MemberBinding>();
        foreach (string f in filters)
        {
            if (!String.IsNullOrEmpty(f))
            {
                dynamicFields.Add(Expression.Bind(resultType.GetMember(f)[0], Expression.Property(sourceItem, inventoryList.ElementType.GetProperty(f))));
            }
        }
        Expression selector = Expression.Lambda(Expression.MemberInit(Expression.New(resultType.GetConstructor(Type.EmptyTypes)), dynamicFields), sourceItem);


        var query = inventoryList.Provider.CreateQuery(
                Expression.Call(
                    typeof(Queryable),
                    "Select",
                    new Type[] { inventoryList.ElementType, resultType },
                Expression.Constant(inventoryList), selector));

        var listResult = new List<object>();
        var enumerator = query.GetEnumerator();
        while (enumerator.MoveNext())
        {
            listResult.Add(enumerator.Current);
        }


        gvResults.DataSource = listResult;
        gvResults.DataBind();

}

有这样的课程

 public class linqResult
 {
  public string ItemID {get; set;}
  public string ItemDescription {get; set;}
  public string CustomsValue {get; set;}
 }

我的目标是拥有完整列表，然后只显示客户想要的属性。

Answer 1

  List<LinqResult> inventoryList = (from cust in db.Customers
                             join product in db.Products on cust.customerID equals product.customerID
                             join inventory in db.Inventories on product.itemID equals inventory.ItemId
                             join warehouse in db.Warehouses on inventory.WarehouseId equals warehouse.Id
                             where cust.customerID == customer.CustomerId
                             select cust).OrderBy(k => k.ItemID).ToList();

这有用吗？我在网站上打了它，但是jist只是从查询中获取你的列表集合，然后在你得到它时将它转换成你的LinqResult。您可能需要将其强制转换为ToList - 但请使用它，看看它为您做了什么。

从现有列表构建动态linq选择查询

1 个答案: