集中或合并 LINQ 选择
本文关键字:选择 LINQ 合并 集中 | 更新日期: 2023-09-27 18:36:35
如何重构此代码以便集中投影?
public IEnumerable<ItemDto> GetItemsByType(int itemId, ItemType itemType)
{
IEnumerable<ItemDto> items = null;
try
{
var tempItems= _Items.Get(i => i.ItemId == itemId
&& o.Active == true);
switch (itemType)
{
case ItemType.Normal:
items = from item in tempItems
select new ItemDto
{
// many fields here
};
break;
case ItemType.Damaged:
items = from item in tempItems
join itemDetail in _ItemDetails.Get() on item.ID equals itemDetail.ItemID
select new ItemDto
{
// many fields here
};
break;
case ItemType.Fixed:
items = from item in tempItems
join itemDetail in _ItemDetails.Get() on item.ID equals itemDetail.ItemID
where item.Status.ToLower() == "fixed"
select new ItemDto
{
// many fields here
};
break;
// more case statements here...
default:
break;
}
}
catch { ... }
}
基本上,我有很多案例陈述,每个案例陈述都有一个很长的投影。我担心一旦 DTO 需要更改,例如添加新字段,其他情况的预测可能彼此不一致(忘记或错过更新)。我怎样才能集中起来?
你可以做这样的事情:
var baseQuery = from item in tempItems select item;
switch (itemType)
{
case ItemType.Fixed:
baseQuery = from item in baseQuery where item.ID equals itemID select item;
break;
}
return (from item in baseQuery select new ItemDTO (...projection here... ));
你能这样处理吗?
var query = tempItems.AsQueryable();
switch(itemType)
{
case ItemType.Damaged:
query.Join(...);
break;
case ItemType.Fixed:
query.Where(...);
}
query.Select(e => new ItemDto{//Lots of properties});
return query.ToList();
这种方法会有帮助吗?
public IEnumerable<ItemDto> GetItemsByType2(int itemId, ItemType itemType)
{
var cases = new Dictionary<ItemType, Func<IEnumerable<ItemDto>, IEnumerable<ItemDto>>>()
{
{ ItemType.Normal, xs => xs },
{ ItemType.Damaged, xs =>
from item in xs
join itemDetail in _ItemDetails.Get() on item.ID equals itemDetail.ItemID
select item },
{ ItemType.Fixed, xs =>
from item in xs
join itemDetail in _ItemDetails.Get() on item.ID equals itemDetail.ItemID
where item.Status.ToLower() == "fixed"
select item },
};
return cases[itemType](_Items.Get(i => i.ItemId == itemId && o.Active == true))
.Select(x => new ItemDto { .... });
}