返回2列,Id和count,从EF作为Dictionary <int,int>

Question

我在两个表之间有一个FK关系,但是为了这个查询的目的,我需要得到每个FK的行数.

例如,我有一个CareTaker表CareTakerId作为PK; 还有一张FK 的Animal表格CareTakerId.给出一个列表CareTakerIds,我想要每个看护者负责的所有AnimalIds.像这样的东西:

select CareTakerId, count(1) 
from Animal
where CareTakerId in (1,2,3,4)
    and AnimalTypeId = 3
group by CareTakerId

哪个回报

CareTakerId | No ColumnName
1           | 42
2           | 6

我如何在EntityFramework中执行此操作？我需要这个结果,所以我认为我会把它作为一个Dictionary<int,int>(Dictionary<CareTakerId,Count>) - 但我无法弄清楚如何为它编写EF查询..这是我到目前为止所拥有的:

query
    .Where(r => r.AnimalTypeId == animalTypeId 
             && careTakerIds.Contains(r => r.CareTakerId))
    .GroupBy(r => r.CareTakerId)
    // Not sure what to write here; r.CareTakerId doesn't exist
    .Select(r => new {r.key, r.value }) 
    .ToDictionary(kvp => kvp.Key, kvp => kvp.value);

如何CareTakerId在实体框架中选择和计算(1)？

Answer 1

在你的这个Select:

//...
//You have groups here, 
//so you can call Count extension method to get how many elements belong to the current group
.Select(g => new {CareTakerId=g.Key,Count= g.Count() })
.ToDictionary(e=> e.CareTakerId,e=> e.Count);