I have a custom List (MyCustomList) that implements List(Of MyCustomClass).
I want to run a LINQ query against that and return a filtered MyCustomList.
Public ReadOnly Property DebitTransactions As MyCustomList
Get
Return From item In Me Where item.IsDebit = True Select item
End Get
End Property
I get a type conversion here because the LinQ query doesn't return the list in the same MyCustomList that it was filtering. It cannot convert a WhereSelectListIterator object (which is returned) to a MyCustomClass.
I really need the filtered results to be in the same format they came in as. Any suggestions?
If you implement your own Where exthension method you can keep using linq syntax.
public class MyCustomList : List<MyCustomClass>
{
public MyCustomList() : base()
{
}
public MyCustomList(IEnumerable<MyCustomClass> coll) : base(coll)
{
}
}
public static class MyCustomListExtensions
{
public static MyCustomList Where(this MyCustomList myList, Func<MyCustomClass, bool> predicate)
{
return new MyCustomList(Enumerable.Where(myList, predicate));
}
}
public class MyCustomClass
{
public int Int1 { get; set; }
public string Str1 { get; set; }
}
And here I'm using the custom Where implementation:
var myList = new MyCustomList()
{
new MyCustomClass() { Int1 = 1},
new MyCustomClass() { Int1 = 2},
new MyCustomClass() { Int1 = 3},
};
MyCustomList filteredList = from item in myList where item.Int1 > 1 select item;
Assert.AreEqual(2, filteredList.Count);
You have to iterate the list, add them to a collection, and return the collection. Linq doesn't support, directly, conversion of iterators to custom return types other than List, arrays and Dictionaries.
Related
I have 4 classes namely ClassA, ClassADto, ClassAA(inner class to ClassA) and the final Result class.
ClassAA
{
public int HouseNumber{get;set;}
public string StreetName{get;set;}
public string State{get;set;}
}
ClassA
{
public int Age{get;set;}
public string Name{get;set;}
public ClassAA AObj[get;set;}
}
ClassADto
{
public int Age{get;set;}
public string Name{get;set;}
}
class Result
{
public string StreetName{get;set;}
public int TotalCount{get;set;}
public int TodaysDate{get;set;}
public List<ClassADto> AObjectsList{get;set;}
}
Now my aim is map the 'Result' class with the List of ClassA object to fill it the property 'AObjectsList' as below:
Result data= map mapper.map>(obj);
Also at the same time in automapper i want to use custom function either using 'Resolve' or 'AfterMap' to set properties like 'TodaysDate' to current datetime of system and property 'TotalCount' by counting the number of data.
I tried in many ways using 'CreateMap' and also used 'ForMembers' as from 'classAA' we only need the 'StreetName' but it didn't work. Need some help please.
One time typing approach ;)
public static Result ToResult(this List<ClassA> users)
{
return new Result
{
TotalCount = users.Count,
TodaysDate = DateTime.Today,
AObjectsList = users
.Select(user => new ClassADto
{
Name = user.Name,
Age = user.Age
})
.ToList()
};
}
// Usage
var users = new List<ClassA> { new ClassA(), new ClassA() };
var result = users.ToResult();
I have this problem with lists and I can't seem to fix it
I have this class that implement a interface that has the following method.
public List<T> CalculateWad<T, TH>(
List<T> outputList,
List<TH> inputList,
bool flag)
{
...
}
Now, I have a outputlist and a inputlist with a common field Contract. I need to delete in outputlist all contracts that exist in inputlist.
It has to be as generic as possible. I can't seem to be able to get the fields of the lists.
Any ideas?
In order to access the Contract property, the generics T and TH must implement an interface with the Contract property.
Documentation : where (generic type constraint) (C# Reference)
interface IContractable { string Contract { get; } }
Then your class containing the CalculateWad method must be define as follow :
class MyClass<T, TH>
where T : IContractable
where TH : IContractable
{
public List<T> CalculateWad(List<T> outputList, List<TH> inputList, bool flag)
{
return outputList
.Where(o =>
inputList.Select(i => i.Contract).Contains(o.Contract) == false)
.ToList();
}
}
This should to the job, by adding a common IHasContract interface that both T and TH must implement:
class Program
{
static void Main(string[] args)
{
}
private IList<T> CalculateWad<T, TH>(IList<T> output,
IList<TH> input, bool flag)
where T : IHasContract
where TH : IHasContract
{
var contracts = new HashSet<string >(input.Select(i => i.Contract));
var qry = from o in output
where !contracts.Contains(o.Contract)
select o;
return qry.ToList();
}
private sealed class Contract
{
}
private interface IHasContract
{
string Contract { get; }
}
private sealed class Foo : IHasContract
{
public string Contract { get; set; }
}
private sealed class Bar : IHasContract
{
public string Contract { get; set; }
}
}
Note that is does not modify output, which you mention in the text. It does, however, return a new altered copy of the list, which may be rather what the method signature describes.
So this is your interface:
public List CalculateWad( List outputList, List inputList, bool flag) {
...
}
And you need to do this? Assumes that the objects in each list can be compared by their equals method.
public List<T> CalculateWad<T, TH>( List<T> outputList, List<TH> inputList, bool flag) {
// cast list to be regular object lists
List out = (List) outputList;
List in = (List) inputList;
for(Object object : in){
out.remove(object); // this looks for an object that matches using contract.equals(object)
}
}
What is flag variable for?
I am creating a fluent HtmlHelper in MVC - to create a grid based on HTML.
I am aware of mvc contrib and WebGrid - but I am making my own and have a specific problem:
I have to enter this:
#Html.DSGridFor().AddColumn(x=>x.FirstOrDefault().Message)
but I want to be able to type this:
#Html.DSGridFor().AddColumn(x=>x.Message)
The code that gets called when I start with #Html.DSGridFor() - taking in the page based model.
public static DSGridHelper<TModel> DSGridFor<TModel>(this HtmlHelper<TModel> html)
{
return new DSGridHelper<TModel>(html);
}
and then within the class DSGridHelper I have this:
public DSGridHelper<TModel> AddColumn(Expression<Func<TModel, dynamic>> property, string HeaderText = null)
{
string ColumnName = (property.Body as MemberExpression).Member.Name;
DSGridColumn DSGC = new DSGridColumn();
DSGC.ColumnName = ColumnName;
DSGC.HeaderText = HeaderText ?? ColumnName;
DSColumnList.Add(DSGC);
return this;
}
public List<DSGridColumn> DSColumnList { get; set; }
and the column class at the moment is really basic:
public class DSGridColumn
{
public DSGridColumn()
{
}
public string ColumnName { get; set; }
public string HeaderText { get; set; }
}
I can get this code working fine with string based column names, but I want the declaring code in the razor page to be simple in format and strongly typed. At the moment I have to type x=>x.First().Message but I really only need x=>x.Message to identify the column.
I appreciate any help.
UPDATE
Thanks to Justin I can now provide my/our code.
View:
#(Html.DSGridFor3().AddColumn(x => x.Message)
.AddColumn(x => x.Host)
.ToMvcString())
HTML Helper call:
public static DSGridHelper3<T> DSGridFor3<T>(this HtmlHelper<IEnumerable<T>> htmlHelper)
{
return new DSGridHelper3<T>(htmlHelper);
}
Returning class:
public class DSGridHelper3<T>
{
private HtmlHelper _htmlHelper;
//private IEnumerable<T> _dataList;
public List<DSGridColumn> DSColumnList { get; set; }
public DSGridHelper3(HtmlHelper<IEnumerable<T>> htmlHelper)
{
_htmlHelper = htmlHelper;
// _dataList = htmlHelper.ViewData.Model;
DSColumnList = new List<DSGridColumn>();
}
public DSGridHelper3<T> AddColumn(Expression<Func<T, object>> property)
{
string columnName = (property.Body as MemberExpression).Member.Name;
DSGridColumn DSGC = new DSGridColumn();
DSGC.ColumnName = columnName;
DSGC.HeaderText = columnName;
DSColumnList.Add(DSGC);
return this;
}
public MvcHtmlString ToMvcString()
{
sb.Append("<table>");
sb.Append("<tr>");
sb.Append("<td>");
sb.Append("hello world within a table");
sb.Append(#"</td>");
sb.Append("<td>");
sb.Append("hello world within a table");
sb.Append(#"</td>");
sb.Append(#"</tr>");
sb.Append(#"</table>");
return new MvcHtmlString(sb.ToString());
}
}
UPDATE 2
If you wanted to manually insert a different type (perhaps because you are going to get a small amount of table data from ViewData rather than the model of the page) then here is some more code:
View:
#(Html.DSGridFor3<DanSoftware.MVC.Areas.Errors.Code.ELMAH_Error>().AddColumn(x => x.Message).ToMvcString();)
Alternative signature for the DSGridHelper ...helper
public static DSGridHelper3<T> DSGridFor3<T>(this HtmlHelper htmlHelper)
{
return new DSGridHelper3<T>(htmlHelper);
}
Additional constructor:
public DSGridHelper3(HtmlHelper htmlHelper)
{
_htmlHelper = htmlHelper;
// _dataList = htmlHelper.ViewData.Model;
DSColumnList = new List<DSGridColumn>();
}
Hope this helps someone and thanks Justin!
I dont have Visual Studio with me but I'll take a stab at this...
I would take in a collection as a datatype either in your DsGridFor method or in the AddColumn method. This will allow you to send Strongly-typed arguments from a collection. Say you wanted a generic method of AddColumn for a given collection with access to the class properties vs the collection methods, it would look something like this (just an example):
public static DSGridHelper<T> AddColumn<T>(this HtmlHelper<IEnumerable<T>> htmlHelper, Expression<Func<T, object>> property) where T : class
{
string columnName = (property.Body as MemberExpression).Member.Name;
DSGridColumn DSGC = new DSGridColumn();
DSGC.ColumnName = ColumnName;
DSGC.HeaderText = HeaderText ?? ColumnName;
DSColumnList.Add(DSGC);
return this;
}
For your situation, to new-up a DsGridHelper class I might explicitly set a model-type first and then add overloads as I go:
public static DSGridHelper<T> DSGridFor<T>(this HtmlHelper<IEnumerable<T>> htmlHelper) where T : class
{
return new DSGridHelper<T>(htmlHelper);
}
And then my DsGridHelper might look something like this:
public class DsGridHelper<T>
{
private HtmlHelper _htmlHelper;
private IEnumerable<T> _dataList;
public DsGridHelper(HtmlHelper<IEnumerable<T>> htmlHelper)
{
_htmlHelper = htmlHelper;
_dataList = htmlHelper.ViewData.Model;
}
public DsGridHelper<T> AddColumn(Expression<Func<T, object>> property)
{
string columnName = (property.Body as MemberExpression).Member.Name;
DSGridColumn DSGC = new DSGridColumn();
DSGC.ColumnName = ColumnName;
DSGC.HeaderText = HeaderText ?? ColumnName;
DSColumnList.Add(DSGC);
return this;
}
}
Not sure if what I am trying is possible or not, but I'd like to reuse a linq expression on an objects parent property.
With the given classes:
class Parent {
int Id { get; set; }
IList<Child> Children { get; set; }
string Name { get; set; }
}
class Child{
int Id { get; set; }
Parent Dad { get; set; }
string Name { get; set; }
}
If i then have a helper
Expression<Func<Parent,bool> ParentQuery() {
Expression<Func<Parent,bool> q = p => p.Name=="foo";
}
I then want to use this when querying data out for a child, along the lines of:
using(var context=new Entities.Context) {
var data=context.Child.Where(c => c.Name=="bar"
&& c.Dad.Where(ParentQuery));
}
I know I can do that on child collections:
using(var context=new Entities.Context) {
var data=context.Parent.Where(p => p.Name=="foo"
&& p.Childen.Where(childQuery));
}
but cant see any way to do this on a property that isnt a collection.
This is just a simplified example, actually the ParentQuery will be more complex and I want to avoid having this repeated in multiple places as rather than just having 2 layers I'll have closer to 5 or 6, but all of them will need to reference the parent query to ensure security.
If this isnt possible, my other thought was to somehow translate the ParentQuery expression to be of the given type so effectively:
p => p.Name=="foo";
turns into:
c => c.Dad.Name=="foo";
but using generics / some other form of query builder that allows this to retain the parent query and then just have to build a translator per child object that substitutes in the property route to the parent.
EDIT:
Following on from comments by #David morton
Initially that looks like I can just change from Expression to a delegate function and then call
.Where(ParentQuery()(c.Dad));
However I am using this in a wider repository pattern and cant see how I can use this with generics and predicate builders - I dont want to retrieve rows from the store and filter on the client (web server in this case). I have a generic get data method that takes in a base expression query. I then want to test to see if the supplied type implements ISecuredEntity and if it does append the securityQuery for the entity we are dealing with.
public static IList<T> GetData<T >(Expression<Func<T, bool>> query) {
IList<T> data=null;
var secQuery=RepositoryHelperers.GetScurityQuery<T>();
if(secQuery!=null) {
query.And(secQuery);
}
using(var context=new Entities.Context()) {
var d=context.GetGenericEntitySet<T>();
data=d.ToList();
}
return data;
}
ISecuredEntity:
public interface ISecuredEntity : IEntityBase {
Expression<Func<T, bool>> SecurityQuery<T>();
}
Example Entity:
public partial class ExampleEntity: ISecuredEntity {
public Expression<Func<T, bool>> SecurityQuery<T>() {
//get specific type expression and make generic
Type genType = typeof(Func<,>).MakeGenericType(typeof(ExampleEntity), typeof(bool));
var q = this.SecurityQuery(user);
return (Expression<Func<T, bool>>)Expression.Lambda(genType, q.Body, q.Parameters);
}
public Expression<Func<ExampleEntity, bool>> SecurityQuery() {
return e => e.OwnerId==currentUser.Id;
}
}
and repositoryHelpers:
internal static partial class RepositoryHelpers {
internal static Expression<Func<T, bool>> SecureQuery<T>() where T : new() {
var instanceOfT = new T();
if (typeof(Entities.ISecuredEntity).IsAssignableFrom(typeof(T))) {
return ((Entities.ISecuredEntity)instanceOfT).SecurityQuery<T>();
}
return null;
}
}
EDIT Here is the (eventual) solution
I ended up going back to using expressions, and using LinqKit Invoke. Note: for EF I also had to call .AsExpandable() on the entitySet
The key part is being able to call:
Product.SecureFunction(user).Invoke(pd.ParentProduct);
so that I can pass in the context into my parent query
My end classes look like:
public interface ISecureEntity {
Func<T,bool> SecureFunction<T>(UserAccount user);
}
public class Product : ISecureEntity {
public Expression<Func<T,bool>> SecureFunction<T>(UserAccount user) {
return SecureFunction(user) as Expression<Func<T,bool>>;
}
public static Expression<Func<Product,bool>> SecureFunction(UserAccount user) {
return f => f.OwnerId==user.AccountId;
}
public string Name { get;set; }
public string OwnerId { get;set; }
}
public class ProductDetail : ISecureEntity {
public Expression<Func<T,bool>> SecureFunction<T>(UserAccount user) {
return SecureFunction(user) as Expression<Func<T,bool>>;
}
public static Func<ProductDetail,bool> SecureFunction(UserAccount user) {
return pd => Product.SecureFunction(user).Invoke(pd.ParentProduct);
}
public int DetailId { get;set; }
public string DetailText { get;set; }
public Product ParentProduct { get;set; }
}
Usage:
public IList<T> GetData<T>() {
IList<T> data=null;
Expression<Func<T,bool>> query=GetSecurityQuery<T>();
using(var context=new Context()) {
var d=context.GetGenericEntitySet<T>().Where(query);
data=d.ToList();
}
return data;
}
private Expression<Func<T,bool>> GetSecurityQuery<T>() where T : new() {
var instanceOfT = new T();
if (typeof(Entities.ISecuredEntity).IsAssignableFrom(typeof(T))) {
return ((Entities.ISecuredEntity)instanceOfT).SecurityQuery<T>(GetCurrentUser());
}
return a => true; //returning a dummy query
}
}
Thanks for the help all.
You're overthinking it.
First, don't return an Expression<Func<Parent, bool>>, that'll require you to compile the expression. Return simply a Func<Parent, bool> instead.
Next, it's all in how you call it:
context.Children.Where(c => c.Name == "bar" && ParentQuery()(c.Dad));
context.Parents.Where(ParentQuery());
If I have classes of Type A and B:
public class A
{
public int TotalCount;
public string Title;
}
public class B
{
public int Count;
public string Title;
}
I have a list of instances A instances, what is the most efficient way to create and populate a List of type B using Linq?
List<B> listB = listA.Select(a => new B()
{
Count = a.TotalCount,
Title = a.Title
}).ToList();
Does the same as eduncan's solution with different syntax. Take your pick..
var list =
from a in TableA
select new B {
Count = a.TotalCount,
Title = a.Title
};
You new up an instance of B in your select clause, and assign the properties using the inline property assignment feature in C# 3.0.
The advantages of mapping it inline comes from deferred execution of your Linq statement. Linq will map the modified statement, and execute it from your IQueryable. For example:
public class ClassA
{
public int TotalCount;
public string Title;
}
public class ClassB
{
public int Count;
public string Title;
}
public IQueryable<ClassB> FetchAllOfClassB()
{
var list =
from a in TableOfClassA
select new ClassB {
Count = a.TotalCount,
Title = a.Title
};
return list.AsQueryable();
}
Technically, the AsQueryable() is a bit redundant. Sometimes I use it to make it a point, others say it is absolutely required. None the less, the list object itself is IQueryable of ClassB.
Then you can call FetchAllOfClassB() further up the chain, and use IQuerable. It's pretty slick, and efficient.
Hmm, off the top of my head (so there will probably be errors!):
List< B > = from a in listOfA select new B(a.count, a.title);
might do the trick.