[英]Mapping one to many with Dapper
Trying to figure this out, but I can't get it to work. 试图弄清楚这一点,但我无法正常工作。 This query:
该查询:
select MultiCollections.*, Collections.* from MultiCollections
left join MultiCollectionCollections on MultiCollections.Id = MultiCollectionCollections.MultiCollectionId
left join Collections on MultiCollectionCollections.CollectionId = Collections.Id
where MultiCollections.UserId=5
This will return this data: 这将返回以下数据:
As you can see, row 1 and 2 are from the same Title.
如您所见,第1行和第2行来自同一标题。 The data behind them are books.
它们背后的数据是书籍。 Row 3 and 4 are also collections but don't have books.
第3行和第4行也是馆藏,但没有书籍。
I have two objects in my code: MultiCollection Collection 我的代码中有两个对象:MultiCollection集合
Both correspond with the data given in the result of the query: Id, UserId and Title are for object MultiCollection. 两者都与查询结果中给出的数据相对应:Id,UserId和Title用于对象MultiCollection。 Other data are for the object Collection.
其他数据用于对象Collection。
I expect to see three MultiCollections in my C# code: Action Drama Fiction 我希望在我的C#代码中看到三个MultiCollection:Action Drama Fiction
Action will have 2 collections. 动作将有2个集合。 Drama and Fiction should be empty.
戏剧和小说应该是空的。
Instead, I get 4 MultiCollections and none of them contains Collections. 相反,我得到了4个MultiCollections,它们都不包含Collections。 My C# code:
我的C#代码:
public IEnumerable<MultiCollection> GetAll(int userId)
{
string query = @"select MC.*, C.* from MultiCollections MC
left join MultiCollectionCollections MCC on MC.Id = MCC.MultiCollectionId
left join Collections C on MCC.CollectionId = C.Id
where UserId=" + userId;
using (DbConnection connection = ConnectionFactory())
{
connection.Open();
return connection.Query<MultiCollection, List<Collection>, MultiCollection>(query,
(a, s) =>
{
a.Collections = s;
return a;
});
}
}
When running the code I would expect this: 运行代码时,我期望这样:
Action
Collections
-> Book 1
-> Book 2
Drama
Collections
Null
Fiction
Collections
Null
I have no idea what I'm doing wrong. 我不知道我在做什么错。
Your c# code should of look like this: 您的C#代码应如下所示:
public IEnumerable<MultiCollection> GetAll(int userId)
{
string query = @"select MC.*, C.* from MultiCollections MC
left join MultiCollectionCollections MCC on MC.Id = MCC.MultiCollectionId
left join Collections C on MCC.CollectionId = C.Id
where UserId=" + userId;
using (DbConnection connection = ConnectionFactory())
{
connection.Open();
return connection.Query<MultiCollection, Collection, MultiCollection>(query,
(a, s) =>
{
a.Collections = new List<Collection>();
a.Collections.Add(s);
return a;
}, splitOn: "MultiCollectionId,CollectionId"););
}
}
Notice, that .Query<MultiCollection, Collection, MultiCollection>
is a Collection
not List<Collection>
and it is doing .add()
and not setter. 通知,即
.Query<MultiCollection, Collection, MultiCollection>
是一个Collection
不List<Collection>
和它做.add()
而不是设置器。
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