I have a simple hiearchical list of objects "ProductGroups" (IQueryable).
Each "ProductGroup" has a collection of ProductGroups called "Children",an integer ParentId field and a boolean "IsEnabled" field.
public class ProductGroup
{
public int Id;
public int ParentId;
public ICollection<ProductGroup> Children;
public bool IsEnabled;
}
I want to be able to return a tree of ProductGroups where "IsEnabled" is true.
At the moment, if I do
ProductGroups.Where(x => x.IsEnabled)
This returns the enabled products. If I do
ProductGroups.Where(x => x.ParentId == null)
This returns the roots. I want to be able to return a full tree excluding the disabled items in the neatest way possible (i.e. not using for loops after querying the collection).
ProductGroup1 (IsEnabled == true)
|
--------- ProductGroup2 (IsEnabled == true)
| |
| ----------- ProductGroup4 (IsEnabled == false)
|
--------- ProductGroup4 (IsEnabled == false)
i.e. Return ProductGroup1 with 1 child ProductGroup2
Thanks
I'm not sure of your exact needs with the filtered collection. I'm looking at it as a View-Model. And a recursive extension method provides you with a neat way to achieve this filter:
public static class Helper
{
public static ICollection<ProductGroup> EnabledWithChildren(this ICollection<ProductGroup> source)
{
var result = new List<ProductGroup>();
foreach (var ele in source)
{
if(ele.IsEnabled == true)
{
var productGroup = new ProductGroup{Id = ele.Id, IsEnabled = ele.IsEnabled, ParentId = ele.ParentId};
if(ele.Children != null && ele.Children.Count() > 0)
productGroup.Children = ele.Children.EnabledWithChildren();
result.Add(productGroup);
}
}
return result;
}
}
And usage:
public class ProductGroup
{
public int Id;
public int? ParentId;
public ICollection<ProductGroup> Children;
public bool IsEnabled;
static void Main()
{
var filteredProductGroups = ProductsGroups.EnabledWithChildren();
}
}
Related
Thanks in advance. I can get required output when using var but i want to get required output by using Distinct in List<>.
InventoryDetails.cs
public class InventoryDetails
{
public int? PersonalInventoryGroupId { get; set; }
public int? PersonalInventoryBinId { get; set; }
}
InventoryController.cs
[HttpGet("GetInventory")]
public IActionResult GetInventory(int id)
{
//Below code will return distinct record
var inventory = (from i in _context.TempTbl
where i.TempId == id
select new
{
PersonalInventoryBinId = i.PersonalInventoryBinId,
PersonalInventoryGroupId = i.PersonalInventoryGroupId,
}).ToList().Distinct().ToList();
//Below code is not doing distinct
List<InventoryDetails> inventory = (from i in _context.TempTbl
where i.TempId == id
select new InventoryDetails
{
PersonalInventoryBinId = i.PersonalInventoryBinId,
PersonalInventoryGroupId = i.PersonalInventoryGroupId,
}).ToList().Distinct().ToList();
}
If i use var as return type, then i am able to get distinct records. Could some one assist it.
Please try like this it may help.
IList<InventoryDetails> inventory = _context.InventoryDetails.Where(x=>x.TempId == id).GroupBy(p => new {p.PersonalInventoryGroupId, p.PersonalInventoryBinId } )
.Select(g => g.First())
.ToList();
You need to override Equals and GetHashCode.
First, let's see the AnonymousType vs InventoryDetails
var AnonymousTypeObj1 = new { PersonalInventoryGroupId = 1, PersonalInventoryBinId = 1 };
var AnonymousTypeObj2 = new { PersonalInventoryGroupId = 1, PersonalInventoryBinId = 1 };
Console.WriteLine(AnonymousTypeObj1.Equals(AnonymousTypeObj2)); // True
var InventoryDetailsObj1 = new InventoryDetails { PersonalInventoryBinId = 1, PersonalInventoryGroupId = 1 };
var InvertoryDetailsObj2 = new InventoryDetails { PersonalInventoryBinId = 1, PersonalInventoryGroupId = 1 };
Console.WriteLine(InventoryDetailsObj1.Equals(InvertoryDetailsObj2)); // False
You can see the Equals behave differently which make Distinct behave differently. The problem is not var you mentioned in your question but AnonoymizeType
To make Distinct works as you expect, you need to override Equals and GetHashCode
public class InventoryDetails
{
public int? PersonalInventoryGroupId { get; set; }
public int? PersonalInventoryBinId { get; set; }
public override bool Equals(object obj)
{
if (obj == null) return false;
if (obj is InventoryDetails)
{
if (PersonalInventoryGroupId == (obj as InventoryDetails).PersonalInventoryGroupId
&& PersonalInventoryBinId == (obj as InventoryDetails).PersonalInventoryBinId)
return true;
}
return false;
}
public override int GetHashCode()
{
int hash = 17;
hash = hash * 23 + PersonalInventoryBinId.GetHashCode();
hash = hash * 23 + PersonalInventoryGroupId.GetHashCode();
return hash;
}
}
Another approach would be
List<InventoryDetails> inventory = (from i in TempTbl
where i.TempId == id
select new InventoryDetails
{
PersonalInventoryBinId = i.PersonalInventoryBinId,
PersonalInventoryGroupId = i.PersonalInventoryGroupId,
}).AsQueryable().ToList().Distinct(new customComparer()).ToList();
public class customComparer:IEqualityComparer<InventoryDetails>
{
public bool Equals(InventoryDetails x, InventoryDetails y)
{
if (x.TempId == y.TempId && x.PersonalInventoryBinId == y.PersonalInventoryBinId
&& x.PersonalInventoryGroupId == y.PersonalInventoryGroupId)
{
return true;
}
return false;
}
public int GetHashCode(InventoryDetails obj)
{
return string.Concat(obj.PersonalInventoryBinId.ToString(),
obj.PersonalInventoryGroupId.ToString(),
obj.TempId.ToString()).GetHashCode();
}
}
As said in a comment by Ivan, you make your life difficult by calling ToList before Distinct. This prevents the SQL provider from incorporating the Distinct call into the generated SQL statement. But that leaves the question: what causes the difference?
The first query generates anonymous type instances. As per the C# specification, by default anonymous types (in C#) are equal when their properties and property values are equal (structural equality). Conversely, by default, reference types (like InventoryDetails) are equal when their reference (say memory address) is equal (reference equality or identity). They can be made equal by overriding their Equals and GetHashcode methods, as some people suggested to do.
But that's not necessary if you remove the first ToList():
var inventory = (from i in _context.TempTbl
where i.TempId == id
select new InventoryDetails
{
PersonalInventoryBinId = i.PersonalInventoryBinId,
PersonalInventoryGroupId = i.PersonalInventoryGroupId,
}).Distinct().ToList();
Now the whole statement until ToList() is an IQueryable that can be translated into SQL. The SQL is executed and the database returns a distinct result set of raw records from which EF materializes InventoryDetails objects. The C# runtime code was even never aware of duplicates!
I want to query a list by Linq but filter by an other list containing two elements ( Name, Status) in my example.
This is inspired by an old question I've adapted to my issue.
LINQ: "contains" and a Lambda query
(in this answer it's working for only one element i.e. Status)
I try to use the "contains" method but didn't succeed to filter my list.
I should obtain a result with only two buildings (two, five)
Has anyone an idea where I'm stopped ?
Thanks
Blockquote
public class Building
{
public enum StatusType
{
open,
closed,
weird,
};
public string Name { get; set; }
public StatusType Status { get; set; }
}
private static readonly List<Building> BuildingList = new List<Building>()
{
new Building() {Name = "one", Status = Building.StatusType.open},
new Building() {Name = "two", Status = Building.StatusType.closed},
new Building() {Name = "three", Status = Building.StatusType.weird},
new Building() {Name = "four", Status = Building.StatusType.open},
new Building() {Name = "five", Status = Building.StatusType.closed},
new Building() {Name = "six", Status = Building.StatusType.weird},
};
private void GetResult()
{
var buildingSelect = new List<Building>
{
new Building() {Name = "two", Status = Building.StatusType.closed},
new Building() {Name = "five", Status = Building.StatusType.closed}
};
var q = (from building in BuildingList
where buildingSelect.Contains(building.Name, building.Status)
select building).ToList();
dataGridView1.DataSource = q;
}
The main problem of your LINQ is that you are trying the compare the equality of two Buildings, which LINQ can only compare by their references because Building does not implement IEquatable<Building> nor override object.Equals.
One way to solve it is to manually specify which properties to compare for equality as per #Wayne's answer.
The other way is, if Building instances are meant to be equated by their values and not by their references, implement IEquatable<Building> and override object.Equals:
public class Building : IEquatable<Building>
{
public Building(string name, StatusType status)
{
Name = name;
Status = status;
}
public enum StatusType
{
open,
closed,
weird,
};
public string Name { get; }
public StatusType Status { get; }
public static bool operator ==(Building left, Building right)
=> Equals(left, right);
public static bool operator !=(Building left, Building right)
=> !Equals(left, right);
public override bool Equals(object obj) => Equals(obj as Building);
public bool Equals(Building other)
{
if (ReferenceEquals(this, other))
{
return true;
}
if (ReferenceEquals(other, null) || GetType() != other.GetType())
{
return false;
}
return Name == other.Name && Status == other.Status;
}
public override int GetHashCode()
{
unchecked
{
int hash = 17;
hash = hash * 23 + Name?.GetHashCode() ?? 0;
hash = hash * 23 + Status.GetHashCode();
return hash;
}
}
}
That way, your original code would work because List.Contains will now use your implementation of IEquatable<Building> to check for equality.
You mean something like this?
var q = from b in BuildingList
from bs in buildingSelect
where b.Name == bs.Name && b.Status == bs.Status
select b;
or perhaps:
var q = from b in BuildingList
join bs in buildingSelect
on new { b.Name, b.Status } equals new { bs.Name, bs.Status }
select b;
You can either override the equality in the class itself, IF this makes sense.
Or just make the check normally with Any(), like this:
var q = (from building in BuildingList
where buildingSelect.Any(b => b.Name == building.Name
&& b.Status == building.Status)
select building).ToList();
I have a type which has a default sort order as it implements IComparable<T> and IComparable. I'm not getting the results I expect from LINQ , basically it looks as if the IComparable<T> which the type implements is not being applied.
I thought I would get the result I want with an expression in the form:
var result = MyEnumerable<T>.OrderBy(r => r);
where T itself implements IComparable<T>. It's not happening.
I can see related questions where specific IComparable<T> classes are specified for the sort, but I can't find one which uses the default IComparable<T> implemented by T itself.
My syntax is clearly incorrect. What is the correct syntax please?
Thanks in advance.
OrderBy uses the default comparer Comparer<T>.Default which in turn will default to use the IComparable<T> implementation for T, or the non-generic IComparable if the former does not exist.
This code works:
public class Program
{
static void Main(string[] args)
{
var list = new List<Stuff>
{
new Stuff("one"),
new Stuff("two"),
new Stuff("three"),
new Stuff("four")
};
var sorted = list.OrderBy(x => x);
foreach (var stuff in sorted)
{
Console.Out.WriteLine(stuff.Name);
}
}
}
public class Stuff : IComparable<Stuff>
{
public string Name { get; set; }
public Stuff(string name)
{
Name = name;
}
public int CompareTo(Stuff other)
{
return String.CompareOrdinal(Name, other.Name);
}
}
public static class GenericSorter
{
public static IOrderedEnumerable<T> Sort<T>(IEnumerable<T> toSort, Dictionary<string, SortingOrder> sortOptions)
{
IOrderedEnumerable<T> orderedList = null;
foreach (KeyValuePair<string, SortingOrder> entry in sortOptions)
{
if (orderedList != null)
{
if (entry.Value == SortingOrder.Ascending)
{
orderedList = orderedList.ApplyOrder<T>(entry.Key, "ThenBy");
}
else
{
orderedList = orderedList.ApplyOrder<T>(entry.Key, "ThenByDescending");
}
}
else
{
if (entry.Value == SortingOrder.Ascending)
{
orderedList = toSort.ApplyOrder<T>(entry.Key, "OrderBy");
}
else
{
orderedList = toSort.ApplyOrder<T>(entry.Key, "OrderByDescending");
}
}
}
return orderedList;
}
private static IOrderedEnumerable<T> ApplyOrder<T>(this IEnumerable<T> source, string property, string methodName)
{
ParameterExpression param = Expression.Parameter(typeof(T), "x");
Expression expr = param;
foreach (string prop in property.Split('.'))
{
expr = Expression.PropertyOrField(expr, prop);
}
Type delegateType = typeof(Func<,>).MakeGenericType(typeof(T), expr.Type);
LambdaExpression lambda = Expression.Lambda(delegateType, expr, param);
MethodInfo mi = typeof(Enumerable).GetMethods().Single(
method => method.Name == methodName
&& method.IsGenericMethodDefinition
&& method.GetGenericArguments().Length == 2
&& method.GetParameters().Length == 2)
.MakeGenericMethod(typeof(T), expr.Type);
return (IOrderedEnumerable<T>)mi.Invoke(null, new object[] { source, lambda.Compile() });
}
}
It's the first time that I use EmitMapper.
I have a list of object ex: Customer and I would like to map this list in a ienumerable of CustomerDTO how can I do that?
Tnx
It's straightforward if you have a list and want to convert it to list of DTOs:
var mapper = ObjectMapperManager.DefaultInstance.GetMapper<Customer, CustomerDTO>();
IEnumerable<CustomerDTO> dtos = listOfCustomer.Select(mapper.map);
The preblem is when the list is in another object, for example User and UserDTO:
class User {
public List<Customer> Customers { get; set; }
}
class UserDTO {
public IEnumerable<CustomerDTO> Customers { get; set; }
}
It seems that EmitMapper does not support conversion from List to Enumerable. A way to support it would be:
var customerMapper = ObjectMapperManager
.DefaultInstance.GetMapper<Customer, CustomerDTO>();
var mapper = ObjectMapperManager.DefaultInstance
.GetMapper<User, UserDTO>(
new DefaultMapConfig()
.ConvertUsing<List<Customer>, IEnumerable<CustomerDTO>>(
a => a.Select(customerMapper.Map))
);
This can be done creating a custom class, implementing the interface "ICustomConverterProvider" and adding a ConvertGeneric to the "DefaultMapConfig".
Looking on the source code of EmitMapper, i found a class named "ArraysConverterProvider", which is the default generic converter from ICollections to Arrays.
Adapting the code from this class to work with IEnumerable collections:
class GenericIEnumerableConverterProvider : ICustomConverterProvider
{
public CustomConverterDescriptor GetCustomConverterDescr(
Type from,
Type to,
MapConfigBaseImpl mappingConfig)
{
var tFromTypeArgs = DefaultCustomConverterProvider.GetGenericArguments(from);
var tToTypeArgs = DefaultCustomConverterProvider.GetGenericArguments(to);
if (tFromTypeArgs == null || tToTypeArgs == null || tFromTypeArgs.Length != 1 || tToTypeArgs.Length != 1)
{
return null;
}
var tFrom = tFromTypeArgs[0];
var tTo = tToTypeArgs[0];
if (tFrom == tTo && (tFrom.IsValueType || mappingConfig.GetRootMappingOperation(tFrom, tTo).ShallowCopy))
{
return new CustomConverterDescriptor
{
ConversionMethodName = "Convert",
ConverterImplementation = typeof(GenericIEnumerableConverter_OneTypes<>),
ConverterClassTypeArguments = new[] { tFrom }
};
}
return new CustomConverterDescriptor
{
ConversionMethodName = "Convert",
ConverterImplementation = typeof(GenericIEnumerableConverter_DifferentTypes<,>),
ConverterClassTypeArguments = new[] { tFrom, tTo }
};
}
}
class GenericIEnumerableConverter_DifferentTypes<TFrom, TTo> : ICustomConverter
{
private Func<TFrom, TTo> _converter;
public IEnumerable<TTo> Convert(IEnumerable<TFrom> from, object state)
{
if (from == null)
{
return null;
}
TTo[] result = new TTo[from.Count()];
int idx = 0;
foreach (var f in from)
{
result[idx++] = _converter(f);
}
return result;
}
public void Initialize(Type from, Type to, MapConfigBaseImpl mappingConfig)
{
var staticConverters = mappingConfig.GetStaticConvertersManager() ?? StaticConvertersManager.DefaultInstance;
var staticConverterMethod = staticConverters.GetStaticConverter(typeof(TFrom), typeof(TTo));
if (staticConverterMethod != null)
{
_converter = (Func<TFrom, TTo>)Delegate.CreateDelegate(
typeof(Func<TFrom, TTo>),
null,
staticConverterMethod
);
}
else
{
_subMapper = ObjectMapperManager.DefaultInstance.GetMapperImpl(typeof(TFrom), typeof(TTo), mappingConfig);
_converter = ConverterBySubmapper;
}
}
ObjectsMapperBaseImpl _subMapper;
private TTo ConverterBySubmapper(TFrom from)
{
return (TTo)_subMapper.Map(from);
}
}
class GenericIEnumerableConverter_OneTypes<T>
{
public IEnumerable<T> Convert(IEnumerable<T> from, object state)
{
if (from == null)
{
return null;
}
return from;
}
}
This code is just a copy with a minimum of adaptation as possible and can be applyed to objects with many levels of hierarchy.
You can use the above code with the following command:
new DefaultMapConfig().ConvertGeneric(
typeof(IEnumerable<>),
typeof(IEnumerable<>),
new GenericIEnumerableConverterProvider());
This saved my day and I hope to save yours too! hehehe
I have a nested ObservableCollection<Student>, from which how can I get a particular student based on Id value using LINQ or Lambda ? Here is my Student class:
public class Student
{
public Student()
{
}
public string Name;
public int ID;
public ObservableCollection<Student> StudLists;
}
So each student object can have again student collections and it can go like any number of nested levels. how we can do it LINQ or using Lambda ? I have tried with
var studs = StudCollections.Where(c => c.StudLists.Any(m => m.ID == 122));
But this is not giving exact Student item ? Any idea ?
If you mean you want to search all descendants of StudCollections, then you could write an extension method like so:
static public class LinqExtensions
{
static public IEnumerable<T> Descendants<T>(this IEnumerable<T> source, Func<T, IEnumerable<T>> DescendBy)
{
foreach (T value in source)
{
yield return value;
foreach (T child in DescendBy(value).Descendants<T>(DescendBy))
{
yield return child;
}
}
}
}
and use it like so:
var students = StudCollections.Descendants(s => s.StudLists).Where(s => s.ID == 122);
If you want one student with a matching id, use:
var student = StudCollections.Descendants(s => s.StudLists).FirstOrDefault(s => s.ID == 122);
if (student != null)
{
// access student info here
}