我有一个对象数组DataTestplans
我尝试使用显示的LINQ查询检索特定DataID
和ProductID
的记录,我当前的查询有Distinct()
如果在所有5个提到的属性上取消,我如何根据属性DataID
,TestPlanName
,TCIndexList
和ProductID
检索不同的记录?
DataTestplans: -
[
{
"DataTestPlanID": 0,
"DataID": 19148,
"TestPlanName": "string",
"TCIndexList": "string",
"ProductID": 2033915
},
{
"DataTestPlanID": 0,
"DataID": 19148,
"TestPlanName": "string",
"TCIndexList": "string",
"ProductID": 2033915
},
{
"DataTestPlanID": 0,
"DataID": 19149,
"TestPlanName": "string",
"TCIndexList": "string",
"ProductID": -2642
}
]
LINQ
DataTestPlans_DataID_ProductID = DataTestPlans.Where(c => c.DataID == DataID_ProductID_Record.DataID && c.ProductID == DataID_ProductID_Record.ProductID).Distinct();
答案 0 :(得分:4)
你可以这样做..
DataTestPlans.Where(c => c.DataID == YourInput && c.ProductID == YourInput)
.GroupBy(x => new {x.DataID,x.TestPlanName,x.TCIndexList,x.ProductID})
.Select(x => x.First());
答案 1 :(得分:1)
有两种方法可以做,都在this question中突出显示,不需要IComparer。这是一个你可以玩的快速示例(我没有使用你的实际对象,因为这样更容易解释):
class Program
{
static void Main(string[] args)
{
var persons = Setup();
//option 1, can stream, option suggested by Jon Skeet
//https://stackoverflow.com/a/1300116/897326
var result1 = persons.
DistinctBy(m => new {m.FirstName, m.LastName});
//option 2, cannot stream, but does reference to DistinctBy
//https://stackoverflow.com/a/4158364/897326
var result2 = persons.
GroupBy(m => new { m.FirstName, m.LastName }).
Select(group => group.First());
}
class Person
{
public string FirstName { get; set; }
public string LastName { get; set; }
public string Address { get; set; }
}
private static List<Person> Setup()
{
var p1 = new Person
{
FirstName = "John",
LastName = "Doe",
Address = "USA"
};
var p2 = new Person
{
FirstName = "John",
LastName = "Doe",
Address = "Canada"
};
var p3 = new Person
{
FirstName = "Jane",
LastName = "Doe",
Address = "Australia"
};
var persons = new List<Person>();
persons.Add(p1);
persons.Add(p2);
persons.Add(p3);
return persons;
}
}
public static class LinqExtensions
{
public static IEnumerable<TSource> DistinctBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
{
HashSet<TKey> knownKeys = new HashSet<TKey>();
foreach (TSource element in source)
{
if (knownKeys.Add(keySelector(element)))
{
yield return element;
}
}
}
}
答案 2 :(得分:0)
您必须使用GroupBy()
,这将创建一个可以迭代的IEnumerable<IGrouping<TKey, TElement>>
。您可以使用group.First()或通过组上的某种聚合函数来访问记录。
答案 3 :(得分:0)
您可以使用多个链式崽。如果你正在进行数据库调用,请确保它是IQueryable。一个例子如下
List<SomeClass> c = new List<SomeClass>();
var result = c.Where(x => x.ID == 4).Distinct().Where(y => y.Name == "foo").Distinct();
答案 4 :(得分:0)
您可以实施IEqualityComparer
并在Distinct()
方法中使用默认值。如果您的示例实现DataTestPlansComparer
,您可以在以下示例中使用:
DataTestPlans_DataID_ProductID = DataTestPlans.Where(c => c.DataID == DataID_ProductID_Record.DataID && c.ProductID == DataID_ProductID_Record.ProductID).Distinct(new DataTestPlansComparer());
注意,您的自定义比较器应作为参数传递给Distinct()
方法。
在你的情况下可以是:
public class DataTestPlanComparer : IEqualityComparer<DataTestPlan>
{
public bool Equals(DataTestPlan x, DataTestPlan y)
{
if (Object.ReferenceEquals(x, y)) return true;
if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null))
return false;
return x.DataID == y.DataID && x.ProductID == y.ProductID;
}
public int GetHashCode(DataTestPlan dataTestPlan)
{
if (Object.ReferenceEquals(dataTestPlan, null)) return 0;
int hashDataTestPlanDataID = dataTestPlan.DataID == null ? 0 : dataTestPlan.DataID.GetHashCode();
int hashDataTestPlanProductID = dataTestPlan.ProductID.GetHashCode();
return hashDataTestPlanDataID ^ hashDataTestPlanProductID;
}
}
请按照MSDN指南实施IEqualityComparer。