[英]LINQ Lambda, Group by with list
I'm having some trouble with finding the right syntax to accomplish the following: 我找到正确的语法来完成以下操作时遇到了一些麻烦:
Is it possible with LINQ (Lambda Expression) to .GroupBy data and instead of using the usual .Sum() or .Count() I want the resulting data to be a List of Int. 是否可以使用LINQ(Lambda Expression)到.GroupBy数据,而不是使用通常的.Sum()或.Count(),我希望结果数据是Int的列表。
I defined my own class named: Filter_IDs. 我定义了自己的类:Filter_IDs。 Its constructor needs two parameters:
它的构造函数需要两个参数:
public int? type; // Represents the object_type column from my database
public List<int?> objects; // Represents the object_id column from my database
I want to load data from my database into this object. 我想将数据库中的数据加载到此对象中。 The following LINQ query should result in a List of Filter_IDs:
以下LINQ查询应该生成Filter_ID列表:
The following LINQ query should result in a List of Filter_IDs: 以下LINQ查询应该生成Filter_ID列表:
List<Filter_IDs> filterids = ef.filterLine
.GroupBy(fl => fl.objectType)
.Select(fl => new Filter_IDs { type = fl.Key, objects = fl.Select(x => x.object_id).ToList() })
.ToList();
Using this query gives no building error but gives an 'NotSupportedException' on RunTime. 使用此查询不会产生构建错误,但会在RunTime上显示“NotSupportedException”。
The database looks like this to give you a better understanding of the data: 数据库看起来像这样可以让您更好地理解数据:
http://d.pr/i/mnhq+ (droplr image) http://d.pr/i/mnhq+(droplr image)
Thanks in advance, Gerben 提前谢谢,Gerben
I think the problem is the DB is not able to call ToList in the select, nor to create a new Filter_ID. 我认为问题是DB无法在select中调用ToList,也无法创建新的Filter_ID。
Try something like this : 尝试这样的事情:
List<Filter_IDs> filterids = ef.filterLine.Select(o => new { objectType = o.objectType, object_id=o.object_id})
.GroupBy(fl => fl.objectType).ToList()
.Select(fl => new Filter_IDs { type = fl.Key, objects = fl.Select(x => x.object_id).ToList() })
.ToList();
Maybe you want 也许你想要
IList<Filter_IDs> filterIds = ef.filterline
.Select(fl => fl.objectType).Distinct()
.Select(ot => new Filter_IDs
{
type = ot,
objects = ef.filterline
.Where(fl => fl.objectType == ot)
.Select(fl =>objectType)
.ToList()
}).ToList();
Get the distinct list objectType
and use that to subquery for each list of object_id
. 获取不同的列表
objectType
并将其用于每个object_id
列表的子查询。
However, it seems more efficient to me to just enumerate the values in order, 但是,按顺序枚举值对我来说似乎更有效率,
var results = new List<Filter_IDs>();
var ids = new List<int>();
var first = true;
int thisType;
foreach (var fl in ef.filterLines
.OrderBy(fl => fl.objectType)
.ThenBy(fl => fl.object_Id))
{
if (first)
{
thisType = fl.objectType;
first = false;
}
else
{
if (fl.objectType == thisType)
{
ids.Add(fl.object_Id);
}
else
{
results.Add(new Filter_IDs
{
Type = thisType,
objects = ids
});
thisType = fl.objectType;
ids = new List<int>();
}
}
}
You can use GroupBy on client side: 您可以在客户端使用GroupBy:
List<Filter_IDs> filterids = ef.filterLine
.Select(fl=>new {fl.ObjectType, fl.object_id})
.AsEnumerable()
.GroupBy(fl => fl.objectType)
.Select(fl => new Filter_IDs { type = fl.Key, objects = fl.Select(x => x.object_id).ToList() })
.ToList();
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