[英]How to perform crud operation through linq on database in multiple transaction?
[英]Using Linq to perform CRUD on SETS: how to?
使用Linq,嘗試選擇不在我的本地集中的所有記錄失敗:
var localset = new List<Category>();
localset.Add( new Category { pk1 = 1, pk2 = 1, name = "one" } );
localset.Add( new Category { pk1 = 1, pk2 = 2, name = "two" } );
var dbCategories = dc.Categories;
var diff = dbCategories.Except(localset);
我需要做基本的CRUD:如果不在本地集中,請從數據庫集中刪除,更新存在的地方,然后在不存在的地方添加新的。
我通常會這樣做:
delete from Category C where not exists
( select null from LocalSet L where C.pk1 = L.pk1 and C.pk2 = L.pk2 )
update Category set name = L.name
from LocalSet L
where L.pk1 = Category.pk1 and L.pk2 = Category.pk2
insert into Category (pk1, pk2, name)
select pk1, pk2, name
from LocalSet L
where not exists (
select null from Category C where L.pk1 = C.pk1 and L.pk2 = C.pk2 )
我想起來很容易。 但是,.contains似乎是唯一適用於本地集的方法,並且似乎只比較單個字段。 數據庫表具有組合鍵。
在不更改組合鍵的情況下,有什么方法可以完成這些任務?
對我來說,目前尚不清楚您正在談論哪個包含方法,但是使用復合鍵的一般解決方案是使用匿名類型創建單個值。
例如,如果要加入復合鍵,則可以使用
from x in xs
join y in ys on new { x.k1, x.k2 } equals new { y.k1, y.k2 }
有幫助嗎?
怎么辦呢:
var localset = new List<Category>();
localset.Add(new Category { pk1 = 1, pk2 = 1, name = "one" });
localset.Add(new Category { pk1 = 1, pk2 = 2, name = "two" });
var flattened = localset
.Select(dd => dd.pk1 + "|" + dd.pk2 + "|" + dd.name)
.ToArray();
var dbCategories = dc.Categories;
var diff = from c in dbCategories
let x = c.pk1 + "|" + c.pk2 + "|" + c.name
where !flattened.Contains(x)
select c;
這會將組合鍵轉換為單個數組,使您可以使用Contains
運算符。 讓我知道是否有幫助。 干杯。
您必須實現一個CategoryComparer
,如下所示:
public class CategoryComparer : IEqualityComparer<Category>
{
public bool Equals(Category a, Category b)
{
bool result = false;
if( a.pk1 == b.pk1 && a.pk2 == b.pk2 && a.name == b.name)
result = true;
return result;
}
public int GetHashCode(Category category)
{
if (Object.ReferenceEquals(category, null)) return 0;
return category.pk1.GetHashCode() ^ category.pk2.GetHashCode();
}
}
然后調用Enumerable.Except:
var localset = new List<Category>();
localset.Add( new Category { pk1 = 1, pk2 = 1, name = "one" } );
localset.Add( new Category { pk1 = 1, pk2 = 2, name = "two" } );
var diff = dc.Categories
.AsEnumerable()
.Except(localset, new CategoryComparer());
讓我知道這是否滿足您的需求。
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