How to change value of an object in foreach from IEnumerable<Model>.
Code:
public IEnumerable<Model> ListDaftarPjsp()
{
IEnumerable<Model> list = from x in db.PJSPEvaluation
select new Model
{
foo = x.Foo,
bar = x.Bar
};
foreach (Model item in list) {
item.condition = "example";
}
return list;
}
public class Model{
public string foo{ get; set; }
public string bar { get; set; }
public string condition{ get; set; }
}
I already create Model. Then I am looping result using foreach, then set it. But the Return for conditionstill not changing? how to set condition inside foreach then return it for result
IEnumerable<T> is a query, not a collection. While there is some sort of collection at the other end, the query itself is not the collection. The nature of the collection you are targeting will determine whether or not you can modify the contents.
The general rule of thumb is that you can't expect an IEnumerable<T> to return the same list of objects twice, or even expect that you will be able to enumerate across it more than once - it is perfectly valid (if unusual) for an IEnumerable<T> to enumerate once only and refuse to enumerate a second or third time.
In this case what you have is actually a database query of type IQueryable<Model> that is cast to IEnumerable<Model>. It's still an IQueryable<Model> which means that each time you enumerate across it you will get (probably) the same list of data but in completely new objects. Changing one of the objects won't change all of the objects for the same source record, nor change the contents of the underlying record itself.
If you are trying to modify the returned objects without changing the underlying records (seems to be the case) then you need to materialize the query into a collection in memory. There are a few ways to do this depending on what you're expecting to do with the returned data.
The simplest is to convert the query to an array using the .ToArray() extension method:
public Model[] ListDaftarPjsp()
{
var query = from x in db.PJSPEvaluation
select new Model
{
foo = x.Foo,
bar = x.Bar
};
var list = query.ToArray();
foreach (Model item in list)
{
item.condition = "example";
}
return list;
}
Now the records are in an array in memory and enumeration of that array can be done multiple times returning the same exact objects instead of fetching new copies of the data from the database every time.
Here you are trying to create a list of Model using LINQ, then you are iterating the same for adding an additional property to each item. Then why don't you add the property at the time of creation of the list instead for an additional loop? Make things simple by try something like this:
from x in db.PJSPEvaluation
select new Model
{
foo = x.Foo,
bar = x.Bar,
condition = GetCondition(x.Foo)
};
Where the GetCondition() can be defined as :
private string GetCondition(int foo)
{
if(item.foo == 1)
{
return "a";
}
else if(item.foo == 2)
{
return "b";
}
else
{
return "xx";
}
}
There is already for this topic but there is more efficient way to do this.
Just use List<> instead of Array[].
public List<Model> ListDaftarPjsp()
{
List<Model> list = from x in db.PJSPEvaluation
select new Model
{
foo = x.Foo,
bar = x.Bar
};
foreach (Model item in list)
{
item.condition = "example";
}
return list;
}
public class Model{
public string foo{ get; set; }
public string bar { get; set; }
public string condition{ get; set; }
}
I case you dont want to load items in memory with a .ToArray or .ToList
You can use .Select from Linq.
return myEnumeration.Select(item => {
item.condition = "example";
return item;
})
Related
I need to return one row of List from my function Selectus.
So I pass to the function Selectus object that reflects database table fields and I need to return one row which match the parameter looking_for:
public static List<T> Selectus<T>(string looking_for)
{
//all select data
var db = OrmLiteBaza().Open();//opening database
var select_all_list = db.Select<T>();//getting all data for <T> object works fine
db.Dispose();
//try to select one row - here I have trouble:
var prop = typeof(T).GetProperties();//properties of passed <T> object
var list_selected_record = from records in select_all_list where prop[1].Name == looking_for select records;//tryin to select one record from <T> object as in looking_for variable
return list_selected_record.ToList();//here one record should be returned
}
I do not know how to select one row from the list assuming that T parameter is vary. In SelectusT> method I want to pass as T different objects which reflect fields in database table rather than creatinig separate methods for each select. e.g. call Selectus, where object passed is public class ProductCodes { public int ID { get; set; } public string SapIndex { get; set; } public string SapName { get; set; } }. Then I want to call another Selectus<ProductTypes> for another table etc... So I want to write generic/overall method and use it universally for all types of my objects which reflects the fields of few database tables. The SapIndex property is always in the same place of all objects...
Using prop[1] is incredibly fragile. Who says that the property you're currently interested in is always going to be in second place? What if someone adds another property tomorrow? What if not every T that you use have the same property in the second place on its list of properties? It is quite unclear what your actual goal is here and why you've taken the reflection route.
You would be better off using inheritance or interface implementation here. I'm going to use an interface in this answer, but either would work.
For the sake of clarity, let's assume there is a Code field in all your possible lists, and this is the property you're trying to match with.
Define a reusable interface:
public interface ICodeEntity
{
string Code { get; }
}
Apply your interface to all of the classes that you intend to use for your Selectus method.
public class Person : ICodeEntity
{
public string Code { get; set; }
// And other properties
}
public class Document : ICodeEntity
{
public string Code { get; set; }
// And other properties
}
Add a generic type constraint that limits the use of T only to types that implement your interface.
public static List<T> Selectus<T>(string code)
where T : ICodeEntity
You can now write your code in a way that it relies on the type in question having a Code property, and the compiler will help enforce it.
var db = OrmLiteBaza().Open();
var list = db.Select<T>().ToList();
db.Dispose();
return list.Where(item => item.Code == code).ToList();
Usage examples:
List<Person> peopleWithCodeABC = Selectus<Person>("ABC");
List<Person> documentsWithCodeXYZ = Selectus<Document>("XYZ");
// This will fail if Animal does not implement ICodeEntity
var compilerError = Selectus<Animal>("ABC");
I might not understand fully what you want, but instead of string looking_for you could pass in a Func<,> delegate which acts as a selector.
Something like:
public static List<TField> Selectus<T, TField>(Func<T, TField> selector)
{
var db = OrmLiteBaza().Open();
var select_all_list = db.Select<T>();
db.Dispose();
var list_selected_record = select_all_list.Select(selector); // 'using System.Linq;'
return list_selected_record.ToList();
}
Then I believe it could be called like this:
var list_one = Selectus((ProductCodes x) => x.SapIndex);
var list_two = Selectus((ProductTypes x) => x.SapIndex);
var list_three = Selectus((ProductCodes x) => x.SapName);
With this syntax I leave out the <ProductCodes, string> generic arguments to the method since they can be inferred.
Hmm, maybe you want it in the opposite dimension. You could do:
public static List<T> Selectus<T>(Func<T, bool> predicate)
{
var db = OrmLiteBaza().Open();
var select_all_list = db.Select<T>();
db.Dispose();
var list_selected_record = select_all_list.Where(predicate); // 'using System.Linq;'
return list_selected_record.ToList();
}
with:
var list_one = Selectus((ProductCodes x) => x.SapIndex == "ABC");
var list_two = Selectus((ProductTypes x) => x.SapIndex == "ABC");
var list_three = Selectus((ProductCodes x) => x.SapName == "DaName");
or:
var list_one = Selectus<ProductCodes>(x => x.SapIndex == "ABC");
var list_two = Selectus<ProductTypes>(x => x.SapIndex == "ABC");
var list_three = Selectus<ProductCodes>(x => x.SapName == "DaName");
But if it is going to always be the "same" property, like always x.SapIndex (but for different types of x), then Flater's answer looks good.
Otherwise, if you insist, your reflection approach should be possible. Use propety's name, not its index! Let me try:
public static List<T> Selectus<T>(string looking_for)
{
var db = OrmLiteBaza().Open();
var select_all_list = db.Select<T>();
db.Dispose();
const string prop_name = "SapIndex";
var prop = typeof(T).GetProperty(prop_name); // can blow up for bad T
var list_selected_record = select_all_list
.Where(x => (string)(prop.GetValue(x)) == looking_for); // 'using System.Linq;'
return list_selected_record.ToList();
}
with:
var list_one = Selectus<ProductCodes>("ABC");
var list_two = Selectus<ProductTypes>("ABC");
you can change code to return just one element
public static T Selectus<T>(string looking_for)
{
//all select data
var db = OrmLiteBaza().Open();//opening database
var select_all_list = db.Select<T>();//getting all data for <T> object works fine
db.Dispose();
//try to select one row - here I have trouble:
var prop = typeof(T).GetProperties();//properties of passed <T> object
var list_selected_record = from records in select_all_list where prop[1].Name == looking_for select records;//tryin to select one record from <T> object as in looking_for variable
return list_selected_record.FirstOrDefault();//here one record should be returned
}
I have below class
public class HydronicEquipment
{
public List<LibraryHydronicEquipment> Source { get; set; }
public List<LibraryHydronicEquipment> Distribution { get; set; }
public List<LibraryHydronicEquipment> Terminals { get; set; }
}
and then i have the below class for "libraryHydronicEquipment"
public class LibraryHydronicEquipment : IEquipmentRedundancy
{
public string Name { get; set; }
public RedundancyStatus RedundancyStatus { get; set; }
public EquipmentRedundancy EquipmentRedundancy { get; set; }
}
I am trying to concatenate the list of "LibraryHydronicEquipment" objects available from all three properties (i.e) from source, distribution and terminal and General concatenate method will looks like as this below
var source = hydronicEquipment.Source;
var distribution = hydronicEquipment.Distribution;
var teriminals = hydronicEquipment.Terminals;
Source.Concat(Distribution).Concat(Terminals)
I am trying to achieve the same using reflection and the code looks like as below
foreach (var (systemName, hydronicEquipment) in hydronicSystemEquipment)
{
bool isFirstSystem = true;
var equipmentList = new List<string> { "Source", "Distribution", "Terminals" };
var redundancyequipmentList = GetRedundancyEquipment(hydronicEquipment, equipmentList);
}
and the method GetRedundancyEquipment is looks like below
private static IEnumerable<IEquipmentRedundancy> GetRedundancyEquipment(HydronicEquipment hydronicEquipment, List<string> equipmentList)
{
IEnumerable<IEquipmentRedundancy> equipmentRedundancies = new List<IEquipmentRedundancy>();
dynamic equipmentResults = null;
foreach(var equipment in equipmentList)
{
var componentList = hydronicEquipment.GetType().GetProperty(equipment).GetValue(hydronicEquipment, null) as IEnumerable<IEquipmentRedundancy>;
equipmentResults = equipmentRedundancies.Concat(componentList);
}
return equipmentResults;
}
The problem here is even though i have Source is having list of objects and Distribution is having list of objects, the equipmentResults is giving only one object instead of list of concatenated objects.
I am trying to return the IEnumerable<IEquipmentRedundancy> at the end using reflection method but it seems not working with the above code.
Could any one please let me know how can i achieve this, Many thanks in advance.
GetRedundancyEquipment should preserve your values instead of reassign the reference with each iteration. Here's the fixed version:
private static IEnumerable<IEquipmentRedundancy> GetRedundancyEquipment(HydronicEquipment hydronicEquipment, List<string> equipmentList)
{
IEnumerable<IEquipmentRedundancy> equipmentRedundancies = new List<IEquipmentRedundancy>();
var equipmentResults = new List<IEquipmentRedundancy>();
foreach (var equipment in equipmentList)
{
var componentList = hydronicEquipment.GetType().GetProperty(equipment).GetValue(hydronicEquipment, null) as IEnumerable<IEquipmentRedundancy>;
equipmentResults.AddRange(equipmentRedundancies.Concat(componentList));
}
return equipmentResults;
}
If we look at what you're doing in GetRedundancyEquipment() it becomes clear.
First you create equipmentRedundancies = new List<IEquipmentRedundancy>();
Then you never modify equipmentRedundancies - e.g. via Add(). It remains an empty list until it goes out of scope and is garbage collected.
In a loop you then repeatedly make this assignment equipmentResults = equipmentRedundancies.Concat(componentList);
That is to say: Assign to equipmentResults the concatenation of componentList to equipmentRedundancies.
Note that Concat() is a lazily evaluated linq method. When you actually enumerate it results are produced. It doesn't modify anything, it's more like a description of how to produce a sequence.
So each time through the loop you're assigning a new IEnumerable that describes a concatentaion of an empty list followed by the property that you retrieved with reflection to equipmentResults. Then at the end you return the final one of these concatenations of an empty list and retrieved property.
If you want all of them together, you should concatenate each of them to the result of the previous concatenation, not to an empty list.
I have a class:
public class Doc
{
public int Id {get; set;}
public string Name {get; set;}
public bool IsActive {get; set;}
}
And two lists of Doc type.
How to write LINQ to compare these list and change IsActive property of first list if contains id from second list.
Given that your target list is named targetDocs and the list you want to check for document existance is srcDocs try something like (don't have access to a compiler here so can't test):
targetDocs.ForEach(d => d.IsActive = srcDocs.Any(sd => sd.id == d.Id))
I'm assuming that we are talking about Lists and not other collection types as the ForEach extension method is defined for Lists.
It's better to use the HashSet<T> collection for such operations, it has fast O(1) lookups and there is no real reason to use LINQ for changing property values here. True, we have to create another collection here and it takes time to allocate resources initialize it etc. but if there is one million records it will give huge performance boost.
Provided that docs1 is collection where you would like to change IsActive to true if docs2 collection has Id, you can use :
var ids = new HashSet<int>(docs2.Select(d => d.Id));
foreach(var doc in docs1)
{
// .Contains implementation in HashSet has fast O(1) lookups
doc.IsActive = ids.Contains(doc.Id);
}
You can create your own static method which is responsible for checking active property. I've used enumerators here, it works fast and easy to understand.
static class Program
{
static void Main(string[] args)
{
List<Data> firstInstance = new List<Data>
{
new Data { Id = 1, IsActive = false },
new Data { Id = 2, IsActive = false }
};
List<Data> secondInstance = new List<Data>
{
new Data { Id = 1, IsActive = false },
new Data { Id = 3, IsActive = false }
};
firstInstance.CheckActive(secondInstance);
}
static void CheckActive(this List<Data> firstInstance, List<Data> secondInstance)
{
using (IEnumerator<Data> firstEnumerator = firstInstance.GetEnumerator(), secondEnumerator = secondInstance.GetEnumerator())
{
while (true)
{
if (!firstEnumerator.MoveNext() || !secondEnumerator.MoveNext()) break;
if (firstEnumerator.Current.Id == secondEnumerator.Current.Id) firstEnumerator.Current.IsActive = true;
}
}
}
}
class Data
{
public int Id { get; set; }
public bool IsActive { get; set; }
}
You wrote:
How to write linq to compare these list and change "IsActive" propety of first list if contains id from second list.
Your first list does not have an IsActive property, however the elements of your list have one. Therefore I assume you want the following:
How do I get a sequence of all elements in the first list that have an Id of any of the elements in the second list, so I can change the IsActive properties of those elements.
LINQ is used to enumerate over objects. You can't change the object in the linq statement
If you want to change the objects, you'll have to enumerate over them, for instance with ForEach.
IEnumerable<int> activeIds = secondList.Select(item => item.Id);
IEnumerable<Doc> activeDocs = firstList.Where(item => activedIds.Contains(item.Id));
foreach (Doc activeDoc in activeDocs)
{
activeDoc.IsActive = true;
}
Beware: I did not change ISActive for all inActive docs. If you want that you'll have to foreach all elements from your firstList:
IEnumerable<int> activeIds = secondList.Select(item => item.Id);
foreach (Doc doc in firstList)
{
doc.IsActive = activeIds.Contains(doc.Id);
}
You can use this solution without using linq
foreach(Doc x in list1){
foreach(Doc y in list2){
if(x.id == y.id){
y.IsActive = true;
}
}
}
here is code illustration
interface IObjectA
{
int Id { get; }
string Name { get; }
}
class ObjectA : IObjectA
{
public int Id { get; set; }
public string Name { get; set; }
public ObjectA(int id, string name)
{
Id = id;
Name = name;
}
}
There are two ways for me to generate List<IObjectA> from some other objects
First one is using forloop:
IList<IObjectA> list = new List<IObjectA>();
foreach(var item in someList)
{
list.Add(new ObjectA(item.Id, item.Name));
}
This works perfectly fine.
Then I tried with linq
IList<IObjectA> list = someList.Select(c => new ObjectA(c.Id, c.Name)).ToList();
The compiler will throw me a error basically saying cannot convert ObjectA to IObjectA
To make it work, i have to add
IList<IObjectA> list = someList.Select(c => new ObjectA(c.Id, c.Name)).Cast<IObjectA>().ToList();
Can some one explain why the compile would complain?
Thanks in advance!
The problem is that the linq expressions result in a List<ObjectA>. If you can treat this result as a List<IObjectA>, the compiler might let you add hypothetical OtherObjectA objects to the list, which would blow up on you if you ever tried to cast back to the original List<ObjectA> type, which should be allowed.
To get around this, you can .Cast() the elements before calling .ToList() to get a list of the correct type:
IList<IObjectA> list = someList.Select(c => new ObjectA(c.Id, c.Name)).Cast<IObjectA>().ToList();
You could also use the var keyword:
var list = someList.Select(c => new ObjectA(c.Id, c.Name)).ToList();
But this will still result in a List<ObjectA> and I suspect you need the List<IObjectA> for code further on.
I have a situation where I need to iterate through a collection and add another collection to one of its member using Linq.
For example I have this class
public class Product
{
public string Car { get; set; }
public IEnumerable<Part> Part { get; set; }
}
This class would be within a collection like
IEnumerable<Product> ProductList
How can I populate the Part-property for each Product using GetPartData() with Linq
private IEnumerable<IEnumerable<Part>> GetPartData()
{
return new List<List<Part>>() {
new List<Part>{
new Part(){PartType="11",PartValue=1},
new Part(){PartType="12",PartValue=2}
},
new List<Part>{
new Part(){PartType="21",PartValue=1},
new Part(){PartType="22",PartValue=2}
}
};
}
So ultimately, my ProductList[0].Part should be equal to GetPartData()[0]
If both sequences should be linked via index you can use Enumerable.Zip:
ProductList = ProductList.Zip(GetPartData()
, (product, part) => new Product
{
Car = product.Car,
Part = part
})
.ToList();
Basically, you need to enumerate two IEnumerable at a time to match items from both. The ProductList and the result of GetPartData.
// The two IEnumerable
var products = ProductList;
var parts = GetPartData();
foreach((product, part) in (products, parts)) // will not work :(
{
product.Part = part;
}
Solutions has been debated before.
The Zip method will do it.
// The two IEnumerable
var products = ProductList;
var parts = GetPartData();
products.Zip(parts, (product, part) => product.Part = part).ToList();
The ToList() is really important, to force the execution.
If you are not comfortable with the lambda, you can do it like this:
// The two IEnumerable
var products = ProductList;
var parts = GetPartData();
products.Zip(parts, ProductPartAssociation).ToList();
...
Product ProductPartAssociation(Product product, IEnumerable<Part> part)
{
product.Part = part;
return product; // Actually not used.
}
The result of the Zip is an IEnumerable of whatever the ProductPartAssociation function return. You don't care about it, because what you need is just to be sure that the ProductPartAssociation is executed.