I have a generic list of countries completely filled with countries instances.
List <Country> mylist
This list has different instances of countries but some has the same value for the property "name".
How could i make a distinct over the property of the country "name" to get only the countries with different names?
Thanks.
Greets.
Jose.
Jon suggested MoreLINQ, which is obviously fine, but maybe you want to avoid another dependency. In this case, you can use Enumerable.Distinct with your own IEqualtyComparer<Country>:
var distinctCountries = myList.Distinct(new EqualityComparerForCountryByName());
//IEqualityComparer
class EqualityComparerForCountryByName : IEqualityComparer<Country> {
public bool Equals(Country x, Country y) {
if(Object.ReferenceEquals(x, y)) { return true; }
if(x == null || y == null) { return false; }
return x.Name == y.Name;
}
public int GetHashCode(Country obj) {
if(obj == null) { return 0; }
return obj.Name.GetHashCode();
}
}
You could use MoreLINQ with its DistinctBy method:
var distinctCountries = allCountries.DistinctBy(c => c.Name);
(You don't have to take all of MoreLINQ of course - you could just copy that one method into your code along with the ThrowIfNull extension method, and preserve the licence text appropriately.)
Related
in linq i'm tring to create gridview with dynamic sort columns
can any one help me what is worng on below code and why it does't work
// i created this function to get column value which i need to sorty by
private static string GetReflectedPropertyValue( object subject, string field)
{
object reflectedValue = subject.GetType().GetProperty(field).GetValue(subject, null);
return reflectedValue != null ? reflectedValue.ToString() : "";
}
// this is my grid query
List<ticketSearchRes> tickets = new List<ticketSearchRes>();
// here i deteermined sort direction ascending or desc
bool asc = (gridViewInputsVM.SortDirection == "asc") ? true : false;
bool desc = (gridViewInputsVM.SortDirection != "asc") ? true : false;
IQueryable<ticketSearchRes> source = (from ticket in _db.TblTicket
where (searchRes.assignTic == 1) ? ticket.AssignedTo == CurrentuserId : true
where (searchRes.myTicket == 1 && searchRes.forOthers != 1) ? ticket.CreatedFor == CurrentuserId : true
orderby
asc ? GetReflectedPropertyValue(ticket, "TicketTitle") : "",
// here i need to get dynamic column which i need to sort by
desc ? GetReflectedPropertyValue(ticket, "TicketTitle") : "" descending // doesn't work
select new ticketSearchRes
{
title = (ticket.TicketTitle != null) ? ticket.TicketTitle.ToString() : "",
ticId = ticket.TicketId.ToString()
}).AsQueryable();
How I would solve this is;
The partial class TicketSearchResList is part that fills in the partial method CustomSort. CustomSort accepts a property name and a sort direction and uses Reflection to sort on the named property. So far it should be easy to follow.
public partial class TicketSearchResList : List<TicketSearchRes>
{
partial void CustomSort(string propertyName, string direction);
public void Dump()
{
CustomSort("TicketTitle", "desc");
foreach(var ticket in this)
Console.WriteLine(ticket.ToString()); // For demo purposes
}
}
public partial class TicketSearchResList {
private string propertyName;
private string direction;
partial void CustomSort(string propertyName, string direction)
{
this.propertyName = propertyName;
this.direction = direction;
Sort(Comparer);
}
private int Comparer(TicketSearchRes x, TicketSearchRes y)
{
int directionChanger = direction == "asc" ? 1 : -1;
try
{
PropertyInfo lhs = x.GetType().GetProperty(propertyName);
PropertyInfo rhs = y.GetType().GetProperty(propertyName);
object o1 = lhs.GetValue(x, null);
object o2 = rhs.GetValue(y, null);
if(o1 is IComparable && o2 is IComparable)
{
return ((IComparable)o1).CompareTo(o2) * directionChanger;
}
// No sort
return 0;
}
catch(Exception ex)
{
Debug.WriteLine(ex.Message); // Should log something
return 0;
}
}
The comparison is done using Reflection in the Comparer method. The direction is
used to determine whether to multiply the result by 1 or -1. CompareTo returns
an integer where -1 means less than, 0 means equal to, and 1 means greater than. Thus, if
you multiply the result by -1, you change the direction of the sort.
Finally, the TicketSearchResList class inherits from List<TicketResearchRes>. As you can see, the Dump method calls CustomSort, which, if implemented, yields ordered output.
Also, have a look at the Sort Method documented here by Microsoft
in LINQ how do i search all fields in a table, what do i put for ANYFIELD in the below?
Thanks
var tblequipments = from d in db.tblEquipments.Include(t => t.User).Include(t => t.ChangeLog).Include(t => t.AssetType)
where d."ANYFIELD" == "VALUE" select d;
You can't. You must compare each field individually. It doesn't make sense to compare all fields, given a field may not even be of the same type as the object you're comparing to.
You can, using reflection. Try this:
static bool CheckAllFields<TInput, TValue>(TInput input, TValue value, bool alsoCheckProperties)
{
Type t = typeof(TInput);
foreach (FieldInfo info in t.GetFields().Where(x => x.FieldType == typeof(TValue)))
{
if (!info.GetValue(input).Equals(value))
{
return false;
}
}
if (alsoCheckProperties)
{
foreach (PropertyInfo info in t.GetProperties().Where(x => x.PropertyType == typeof(TValue)))
{
if (!info.GetValue(input, null).Equals(value))
{
return false;
}
}
}
return true;
}
And your LINQ query:
var tblequipments = from d in db.tblEquipments.Include(t => t.User).Include(t => t.ChangeLog).Include(t => t.AssetType)
where CheckAllFields(d, "VALUE", true) select d;
The third parameter should be true if you want to check all fields and all properties, and false if you want to check only all fields.
EDIT: Someone already built this...see here.
Not a full answer, but I don't agree with assertion that you simply can't...
You could come up with an extension method that dynamically filtered the IQueryable/IEnumerable (I'm guessing IQueryable by the db variable) based on properties of a similar type for you. Here's something whipped up in Linqpad. It references PredicateBuilder and is by no means complete/fully accurate, but I tested it out in Linq-to-SQL on some of my tables and it worked as described.
void Main()
{
YourDbSet.WhereAllPropertiesOfSimilarTypeAreEqual("A String")
.Count()
.Dump();
}
public static class EntityHelperMethods
{
public static IQueryable<TEntity> WhereAllPropertiesOfSimilarTypeAreEqual<TEntity, TProperty>(this IQueryable<TEntity> query, TProperty value)
{
var param = Expression.Parameter(typeof(TEntity));
var predicate = PredicateBuilder.True<TEntity>();
foreach (var fieldName in GetEntityFieldsToCompareTo<TEntity, TProperty>())
{
var predicateToAdd = Expression.Lambda<Func<TEntity, bool>>(
Expression.Equal(
Expression.PropertyOrField(param, fieldName),
Expression.Constant(value)), param);
predicate = predicate.And(predicateToAdd);
}
return query.Where(predicate);
}
// TODO: You'll need to find out what fields are actually ones you would want to compare on.
// This might involve stripping out properties marked with [NotMapped] attributes, for
// for example.
private static IEnumerable<string> GetEntityFieldsToCompareTo<TEntity, TProperty>()
{
Type entityType = typeof(TEntity);
Type propertyType = typeof(TProperty);
var fields = entityType.GetFields()
.Where (f => f.FieldType == propertyType)
.Select (f => f.Name);
var properties = entityType.GetProperties()
.Where (p => p.PropertyType == propertyType)
.Select (p => p.Name);
return fields.Concat(properties);
}
}
Useful resources for the unresolved part:
Finding the relevant properties
if this help some one.
first find all properties within Customer class with same type as query:
var stringProperties = typeof(Customer).GetProperties().Where(prop =>
prop.PropertyType == query.GetType());
then find all customers from context that has at least one property with value equal to query:
context.Customer.Where(customer =>
stringProperties.Any(prop =>
prop.GetValue(customer, null) == query));
Hi I want to set the value in the list of objects that matches the given condition in the where clause.Is it possible?
Other work around is to get the list of objects using where clause and then iterate using for Or foreach loop and update the value.
listOfRequestAssigned.Where(x => x.RequestedNumber == CurrentRequest);
I have list listOfRequestAssigned of objects and want to update some propery of the objects that match my search criteria.
class Request
{
bool _requestCompleted;
int _requestedNumber;
public int RequestedNumber
{
get { return _requestedNumber; }
set { _requestedNumber = value; }
}
public bool RequestCompleted
{
get { return _requestCompleted; }
set { _requestCompleted = value; }
}
}
I want to update RequestCompleted property of all objects that match criteria using Linq
You can use ForEach in Linq
listOfRequestAssigned.Where(x => x.RequestedNumber == CurrentRequest).ToList().ForEach(x => x.RequestCompleted = true);
if you have more than one update to do,
listOfRequestAssigned.Where(x => x.RequestedNumber == CurrentRequest).ToList().ForEach(x => { x.RequestCompleted = true; x.OtherProperty = value; } );
Where(...) give you a query, not a Request or a List<Request>. Use FirstOrDefault() if you want to have one (or 0) result, or ToList() if you want to have a list of results on wich you can use ForEach().
In general Linq is a query- not an update tool, but you can use a foreach:
var currentRequests = listOfRequestAssigned
.Where(x => x.RequestedNumber == CurrentRequest);
foreach(var req in currentRequests)
{
req.RequestCompleted = true;
}
Since you have specific collection of type List, you can just use ForEach and a conditional set:
listOfRequestAssigned.Foreach(x => { if (x.RequestedNumber == CurrentRequest) x.RequestCompleted = true;}});
If you had a more generic collection IEnumerable, you can use Select in Linq to build a projection where property will be set as desired (original collection will be left untouched!):
listOfRequestAssigned
.Where(x => x.RequestedNumber == CurrentRequest)
.Select(x => { x.RequestCompleted = true; return x; })
You can use to assign boolean value by following on comparing time. This is the very simplest and smart way for bool property.
listOfRequestAssigned.ForEach(x => x.RequestCompleted = x.RequestedNumber
== CurrentRequest);
I have a List<> of MyPersonObjects. The list is a list of people who I can assign something to. In this list, I include myself (As the task can be assigned to me - and usually is).
So, I want to make sure myself is at the top of the list. I know my personId, which is a property of my person object - so is there a way to order the list to make sure I am first, and then the rest, alphabetically by surname (which is another property of my object)
You can just order the list by two separate criteria, the OrderBy will be the main sort order, if the values are equal (1 for all except you), ThenBy is used.
personList.OrderBy(x => x.Id == myId ? 0 : 1)
.ThenBy(x => x.Surname);
One way is to sort the list by surname with Linq and then remove yourself and put back at the first place:
var personList = db.MyPersonObjects.OrderBy(p => p.Surname).ToList();
var myself = personList.Single(p => p.Id == myselfId);
personList.Remove(myself);
personList.Insert(0, myself);
Or create a custom comparer IComparer<MyPersonObject> where the implementation is something like:
public class PersonCompaper : IComparer<MyPersonObject>
{
private readonly int personId;
public PersonCompaper(int personId)
{
this.personId = personId;
}
public int Compare(MyPersonObject x, MyPersonObject y)
{
if (x.Id == personId && y.Id == personId)
return 0;
if (x.Id == personId)
return 1;
if (y.Id == personId)
return -1;
return string.Compare(x.Surname, y.Surname);
}
}
Then you use it in the OrderBy
db.MyPersonObjects.OrderBy(p => p, new PersonCompaper(myselfId))
While looking though some code of the project I'm working on, I've come across a pretty hefty method which does
the following:
public string DataField(int id, string fieldName)
{
var data = _dataRepository.Find(id);
if (data != null)
{
if (data.A == null)
{
data.A = fieldName;
_dataRepository.InsertOrUpdate(data);
return "A";
}
if (data.B == null)
{
data.B = fieldName;
_dataRepository.InsertOrUpdate(data);
return "B";
}
// keep going data.C through data.Z doing the exact same code
}
}
Obviously having 26 if statements just to determine if a property is null and then to update that property and do a database call is
probably very naive in implementation. What would be a better way of doing this unit of work?
Thankfully C# is able to inspect and assign class members dynamically, so one option would be to create a map list and iterate over that.
public string DataField(int id, string fieldName)
{
var data = _dataRepository.Find(id);
List<string> props = new List<string>();
props.Add("A");
props.Add("B");
props.Add("C");
if (data != null)
{
Type t = typeof(data).GetType();
foreach (String entry in props) {
PropertyInfo pi = t.GetProperty(entry);
if (pi.GetValue(data) == null) {
pi.SetValue(data, fieldName);
_dataRepository.InsertOrUpdate(data);
return entry;
}
}
}
}
You could just loop through all the character from 'A' to 'Z'. It gets difficult because you want to access an attribute of your 'data' object with the corresponding name, but that should (as far as I know) be possible through the C# reflection functionality.
While you get rid of the consecutive if-statements this still won't make your code nice :P
there is a fancy linq solution for your problem using reflection:
but as it was said before: your datastructure is not very well thought through
public String DataField(int id, string fieldName)
{
var data = new { Z = "test", B="asd"};
Type p = data.GetType();
var value = (from System.Reflection.PropertyInfo fi
in p.GetProperties().OrderBy((fi) => fi.Name)
where fi.Name.Length == 1 && fi.GetValue(data, null) != null
select fi.Name).FirstOrDefault();
return value;
}
ta taaaaaaaaa
like that you get the property but the update is not yet done.
var data = _dataRepository.Find(id);
If possible, you should use another DataType without those 26 properties. That new DataType should have 1 property and the Find method should return an instance of that new DataType; then, you could get rid of the 26 if in a more natural way.
To return "A", "B" ... "Z", you could use this:
return (char)65; //In this example this si an "A"
And work with some transformation from data.Value to a number between 65 and 90 (A to Z).
Since you always set the lowest alphabet field first and return, you can use an additional field in your class that tracks the first available field. For example, this can be an integer lowest_alphabet_unset and you'd update it whenever you set data.{X}:
Init:
lowest_alphabet_unset = 0;
In DataField:
lowest_alphabet_unset ++;
switch (lowest_alphabet_unset) {
case 1:
/* A is free */
/* do something */
return 'A';
[...]
case 7:
/* A through F taken */
data.G = fieldName;
_dataRepository.InsertOrUpdate(data);
return 'G';
[...]
}
N.B. -- do not use, if data is object rather that structure.
what comes to my mind is that, if A-Z are all same type, then you could theoretically access memory directly to check for non null values.
start = &data;
for (i = 0; i < 26; i++){
if ((typeof_elem) *(start + sizeof(elem)*i) != null){
*(start + sizeof(elem)*i) = fieldName;
return (char) (65 + i);
}
}
not tested but to give an idea ;)