If I have following type hierarchy:
abstract class TicketBase
{
public DateTime PublishedDate { get; set; }
}
class TicketTypeA:TicketBase
{
public string PropertyA { get; set; }
}
class TicketTypeB:TicketBase
{
public string PropertyB { get; set; }
}
and many more TicketTypes : TicketBase
and want to create a function which selects any property e.g. PropertyA from any ticket type e.g. TicketTypeA
I wrote this function:
private Func<TicketBase, String> CreateSelect(Type t, String FieldName)
{
var parameterExp = Expression.Parameter(t, "sel");
var fieldProp = Expression.PropertyOrField(parameterExp, FieldName);
var lambda = Expression.Lambda<Func<TicketBase, String>>(fieldProp, parameterExp);
return lambda.Compile();
}
and call it on a List<TicketBase> Tickets like so:
Type typeToSelectFrom = typeof(TicketTypeA);
String propertyToSelect = "PropertyA";
Tickets.Select(CreateSelect(typeToSelectFrom, propertyToSelect));
I get the following ArgumentException:
ParameterExpression of type 'TicketTypes.TicketTypeA' cannot be used for delegate parameter of type 'Types.TicketBase'
Anyone know how to fix this?
Well, one option is to include a cast, e.g.
private Func<TicketBase, String> CreateSelect(Type t, String FieldName)
{
var parameterExp = Expression.Parameter(typeof(TicketBase), "sel");
var cast = Expression.Convert(parameterExp, t);
var fieldProp = Expression.PropertyOrField(cast, FieldName);
var lambda = Expression.Lambda<Func<TicketBase, String>>(fieldProp,
parameterExp);
return lambda.Compile();
}
So that calling CreateSelect(typeof(TicketTypeA), "PropertyA") is equivalent to:
Func<TicketBase, string> func = tb => ((TicketTypeA)tb).PropertyA;
Obviously that's going to fail if you apply it to a TicketBase value which refers to (say) a TicketTypeB, but it's hard to avoid that, if you've got a List<TicketBase> or something similar.
Related
Here is the enum extension method to get its description attribute.
public static string GetDescription(this Enum enumeration)
{
if (enumeration == null)
throw new ArgumentNullException();
var value = enumeration.ToString();
var type = enumeration.GetType();
var descriptionAttribute =
(DescriptionAttribute[]) type.GetField(value).GetCustomAttributes(typeof (DescriptionAttribute), false);
return descriptionAttribute.Length > 0 ? descriptionAttribute[0].Description : value;
}
Here is the source object:
public class Account {
public int AccountId {get;set;}
public int AccountStatusId {get;set;}
}
Here is the enum:
public enum AccountStatus {
[Description("N/A")]
None,
[Description("OPEN")]
Open,
[Description("CLOSED")]
Closed,
[Description("BAD CREDIT")
Problem
}
Here is the destination object:
public class GetAccountResponse {
public int AccountId {get;set;}
public string Status {get;set;}
}
Here is my attempt to map (using the latest non-static automapper version). Remember this is during an EF queryable projection.
_config = new MapperConfiguration(cfg => cfg.CreateMap<Account, GetAccountsResponse>()
.ForMember(dest => dest.Status,
opts => opts.MapFrom(src => ((AccountStatus) src.AccountStatusId).GetDescription())));
Here is the projection where query is an IQueryable<Account>:
query.ProjectToList<GetAccountResponse>(_config);
This is the exception I get:
Can't resolve this to Queryable Expression
If you check out the signature of the MapFrom method, you'll notice that one of the overloads takes a parameter of type Expression<Func<TSource, TMember>>.
This suggests that you could write a method which builds an expression tree from ternary expressions that can convert any possible value of your enum to its appropriate string. AutoMapper would then convert this into the appropriate SQL expression via LINQ.
Here's an example which just uses the Enum names themselves: you should be able to adapt it straightforwardly to use your Descriptions:
public static class EnumerableExpressionHelper
{
public static Expression<Func<TSource, String>> CreateEnumToStringExpression<TSource, TMember>(
Expression<Func<TSource, TMember>> memberAccess, string defaultValue = "")
{
var type = typeof(TMember);
if (!type.IsEnum)
{
throw new InvalidOperationException("TMember must be an Enum type");
}
var enumNames = Enum.GetNames(type);
var enumValues = (TMember[])Enum.GetValues(type);
var inner = (Expression)Expression.Constant(defaultValue);
var parameter = memberAccess.Parameters[0];
for (int i = 0; i < enumValues.Length; i++)
{
inner = Expression.Condition(
Expression.Equal(memberAccess.Body, Expression.Constant(enumValues[i])),
Expression.Constant(enumNames[i]),
inner);
}
var expression = Expression.Lambda<Func<TSource,String>>(inner, parameter);
return expression;
}
}
You would use it as follows:
CreateMap<Entry, EntryListItem>()
.ForMember(e => e.ReviewStatus,
c => c.MapFrom(EnumerableExpressionHelper.CreateEnumToStringExpression((Entry e) => e.ReviewStatus)))
Be first, my English is not very good. So I am sorry about that. :)
My question as the title. I have two tables on my database:
Siniflar (SinifId, SinifAdi, Kapasite, OgretmenId)
Ogretmenler (OgretmenId, Ad, Soyad, Brans)
Query:
var siniflar = (from s in db.Siniflar
join o in db.Ogretmenler
on s.OgretmenId equals o.OgretmenId
select new { s.SinifId, s.SinifAdi, s.Kapasite, o.Ad }).ToList();
I want to use the result of the query as a generic, like this:
public List<Siniflar> SiniflariListele()
{
var siniflar = (from s in db.Siniflar
join o in db.Ogretmenler
on s.OgretmenId equals o.OgretmenId
select new { s.SinifId, s.SinifAdi, s.Kapasite, o.Ad }).ToList();
return siniflar;
}
But I get an error. Because the result is anonymous types.
Error: Cannot implicitly convert type System.Collections.Generic.List<AnonymousType#1> to System.Collections.Generic.List<Entity.Siniflar>
How Can I use be generic result. What Can I do for that?
I changed question:
Class:
public class RSiniflar
{
public int SinifId { get; set; }
public string SinifAdi { get; set; }
public int Kapasite { get; set; }
public string OgretmenAdiSoyadi { get; set; }
}
Metod:
public List<RSiniflar> SiniflariListele()
{
List<RSiniflar> siniflar = (from s in db.Siniflar
join o in db.Ogretmenler
on s.OgretmenId equals o.OgretmenId
select new RSiniflar
{
SinifId = s.SinifId,
SinifAdi = s.SinifAdi,
Kapasite = s.Kapasite,
OgretmenAdiSoyadi = o.Ad + ' ' + o.Soyad
}).ToList();
return siniflar;
}
But now error to query: Unable to create a constant value of type 'System.Object'. Only primitive types or enumeration types are supported in this context.
I think, there are a problem on my query... I get an error same when query to var type...
You can return typed list, but you can't return a list of anonymous type. So you need to create a class which will handle your results:
public class A
{
public int SinifId { get; set; }
public int SiniAdi { get; set; }
public int Kapasite { get; set; }
public int Ad { get; set; }
}
And then use it in your query, instead of anonymous objects:
public List<A> SiniflariListele()
{
var siniflar = (from s in db.Siniflar
join o in db.Ogretmenler
on s.OgretmenId equals o.OgretmenId
select new A {
SinifId = s.SinifId,
SinifAdi = s.SinifAdi,
Kapasite = s.Kapasite,
Ad = o.Ad
}).ToList();
return siniflar;
}
You could do the same with an existing class (e.g. Siniflar), but you have to be sure that this class has all necessary properties.
Rather than using new { property1, property2 }, create new Siniflar's in your select.
E.g.
select new Siniflar() {
SinifId = s.SinifId,
SinifAdi = s.SinifAdi,
Kapasite = s.Kapasite }).ToList()
Note: as lazyberezovsky mentioned, your mapping seems to be flawed, as Siniflar does not contain the property Ad.
I am having to generically build a comparative predicate for an Entity Framework Linq query. I'm using reflection and am able to build a single level Lambda expression without any trouble. However where I am starting to get stuck is I have an Entity that has a relationship
public class Parent {
public virtual Child child { get; set; }
.... Other Stuff...
}
public class Child {
public int property { get; set; }
public virtual Parent parent { get; set; }
.... Other Stuff.....
}
How can I can I pass in "Child.property" into Reflection to be able to create a lambda expression comparing and come up with a lambda expression similar to item => item.Child.property == value?
I think you are looking for this:
ParameterExpression parameter = Expression.Parameter(typeof(Parent), "item");
Expression child = Expression.PropertyOrField(parameter, "child");
Expression childProperty = Expression.PropertyOrField(child, "property");
int value = 1;
Expression comparison = Expression.Equal(childProperty, Expression.Constant(value));
Expression<Func<Parent, bool>> lambda = Expression.Lambda<Func<Parent, bool>>(comparison, parameter);
var sample = new[] { new Parent() { child = new Child() { property = 1 } } };
var result = sample.Where(lambda.Compile());
I assume you are wanting a generic solution supporting nested properties:
public Expression buildLambda(Type startingType, string propertyPath, object value) {
var parameter=Expression.Parameter(startingType,"item");
var valueExpression = Expression.Constant(value);
var propertyExpression=propertyPath.Split('.').Aggregate(parameter,(Expression parent,string path)=>Expression.Property(parent,path));
return Expression.Lambda(Expression.Equal(propertyExpression,valueExpression),parameter);
}
What is the problem with the code below?
var newContextElementCollection = new List<NewContextElements>();
var res = from eleCollection in newContextElementCollection
where eleCollection.Property.Except(new List<string> { "Password", "Some Other Value" })
select eleCollection;
The NewContextElementCollection class:
public class NewContextElements
{
public string Property { get; set; }
public string Value { get; set; }
}
I am getting this error:
Instance argument: cannot convert from 'string' to
'System.Linq.IQueryable'
Error 2 'string' does not contain a definition for 'Except' and the best extension
method overload 'System.Linq.Queryable.Except(System.Linq.IQueryable,
System.Collections.Generic.IEnumerable)' has some invalid arguments
Property is a string, not an IEnumerable<string>, which is what your Except clause can work on.
var res= from eleCollection in newContextElementCollection
where eleCollection.Property != "Password"
select eleCollection;
var excluded = new List<string> { "Password","Some Other Value" };
var res = newContextElementCollection.Where(m => !excluded.Contains(m.Property));
MVC3, Entity Framework 4.1 Code first.
Working with 2 tables
Model:
public class UniversityMaster
{
[Key]
public string UniversityId { get; set; }
public string UniversityName { get; set; }
}
public class ProgramMaster
{
[Key]
public string ProgramId { get; set; }
public string ProgramName { get; set; }
public string UniversityId { get; set; }
public virtual UniversityMaster University { get; set; } // navigation property
}
Dynamic expression for sorting (just to avoid a switch case statement):
public virtual IQueryable< ProgramMaster > GetQueryableSort(string sortField="", string sortDirection="")
{
IQueryable<ProgramMaster> query = _dbSet;
ParameterExpression pe = Expression.Parameter(typeof(ProgramMaster), string.Empty);
MemberExpression property = Expression.PropertyOrField(pe, sortField);
//get a exception here if the sort field is of navigation property (University.UniversityName)
LambdaExpression lambda = Expression.Lambda(property, pe);
if (sortDirection == "ASC")
orderbydir = "OrderBy";
else
orderbydir = "OrderByDescending";
MethodCallExpression call = Expression.Call(typeof(Queryable),
orderbydir, new Type[] { typeof(TEntity), property.Type }, query.Expression, Expression.Quote(lambda));
var returnquery = (IOrderedQueryable<ProgramMaster>)query.Provider.CreateQuery< ProgramMaster >(call);
return returnquery;
}
The page is displaying a grid with two columns Program Name and University Name using webgrid. The sorting work fine for Program Name column, however fails if sorted by University Name as this property is in UniversityMaster and the Expression.PropertyOrField searches this property in ProgramMaster. Here is the exception:
University.UniversityName' is not a member of type 'App.Core.Model.ProgramMaster
My question is how I make this work for navigation properties of my model class.
Hope I was able explain the scenario. Any help is appreciated.
Well that's because the MemberExpression is trying to call a member named Univerty.UniversityName on the parameter. What you want to do is call a member named Univerity on the parameter, then call UniversityName on that. Effectively, you need to iteratively resolve the property names.
public virtual IQueryable< ProgramMaster > GetQueryableSort(string sortField = "", string sortDirection = "")
{
IQueryable<ProgramMaster> query = _dbSet;
var propertyNames = sortField.Split(".");
ParameterExpression pe = Expression.Parameter(typeof(ProgramMaster), string.Empty);
Expression property = pe;
foreach(var prop in propertyName)
{
property = Expression.PropertyOrField(property, prop);
}
LambdaExpression lambda = Expression.Lambda(property, pe);
if (sortDirection == "ASC")
orderbydir = "OrderBy";
else
orderbydir = "OrderByDescending";
MethodCallExpression call = Expression.Call(
typeof(Queryable),
orderbydir,
new Type[] { typeof(TEntity), property.Type },
query.Expression,
Expression.Quote(lambda));
var returnquery = (IOrderedQueryable<ProgramMaster>)query.Provider.CreateQuery<ProgramMaster>(call);
return returnquery;
}
Microsoft has a DynamicQueryable class which can be used to dynamically construct certain portions of a LINQ query using strings. With this you can say myQuery.OrderBy("University.UniversityName") and it will handle building the expression. The same library also supports dynamic construction of SELECT and WHERE clauses.
You can find a copy of the source as part of the excellent EntityFramework.Extended package by Loresoft. Microsoft's file is at https://github.com/loresoft/EntityFramework.Extended/blob/master/Source/EntityFramework.Extended/Dynamic/DynamicQueryable.cs