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How to create FUNC Action List with Parameters and Return Values

I am trying to create my first list of actions that I will be able to check a status within the passed object.
But I can't get it to work - its giving me an error on the return type. But if I change the return type to what it wants - then I can't pass values down.
Sample code:
public class Class1
{
public Main()
{
var decisionObject = new DecisionObject();
var decisionList = new List<Func<DecisionObject, DecisionObject>>
{
Method1(decisionObject),
Method2(decisionObject),
Method3(decisionObject)
};
var exitLoop = false;
foreach (var method in decisionList)
{
decisionObject = method(decisionObject);
switch (decisionObject.Status)
{
case Status1:
exitLoop = true;
break;
case Status2:
case Status3:
case Status4:
break;
}
if (exitLoop) break;
}
}
public Func<DecisionObject, DecisionObject> Method1(DecisionObject
decisionObject)
{
decisionObject = SomeOtherMethod(decisionObject);
return decisionObject;
}
}
What am I missing here?

If I'm not mistaken, Method1,Method2, and Method3 are simply supposed to accept a decision object and return a different one. So they would be defined like this (hopefully this is straightforward to you):
DecisionObject Method1(DecisionObject input)
{
var output = SomeMethod(input);
return output;
}
You then want to put all these methods into a list and execute them. To put them into a list, put the method names in the code without parentheses. That tells C# that you want a reference to the method itself, rather than the result of invoking the method.
var decisionList = new List<Func<DecisionObject, DecisionObject>>
{
Method1, //Do not invoke-- just store a reference to the method
Method2,
Method3
};
You can then invoke them by passing the decision object in:
foreach (var func in decisionList)
{
var result = func(decisionObject);
}
The key thing here to remember is that when you put parentheses after a symbol, it tells C# to invoke it. So don't put parentheses if all you want is a reference to the method itself.

decisionObject = SomeOtherMethod(decisionObject)
Isn't probably returning a func but a value.
You could do this:
public Func<DecisionObject, DecisionObject> Method1()
{
var myFunc = (myObject) => SomeOtherMethod(myObject);
return myFunc;
}
That will create and returns a new func that expects one parameter and invokes SomeOtherMethod.
Please note that the parameter of Method1 isn't needed in this approach and so I removed it.

Why DapperRow.GetType() return null?

As far as I knew, Object.GetType() should never return null. (related discussion)
Dapper .Query() return private class DapperRow instances to be treated as dynamic objects. I found a strange thing: DapperRow's .GetType() return null.
Here's the sample code to reproduce the problem. Create a C# project, reference Dapper and open a connection to SQL Server (or other database), use .Query() to execute simple select query and retrieve the first row of result. Use GetType() to get the type of result object, the return value is null.
using (SqlConnection cn = new SqlConnection(csSql))
{
var rec = cn.Query("select getdate() as D").Single();
var t = rec.GetType(); // t == null
Console.WriteLine(t.Name); // null reference exception
}
I suspect that dynamic or private type is the cause of null, so I write my class library for test:
namespace Lib
{
public class Blah
{
public static dynamic SecretObject;
static Blah()
{
SecretObject = new PrivateType();
}
}
class PrivateType
{
}
}
In another project, get the dynamic type static field and call GetType():
dynamic obj = Lib.Blah.SecretObject;
Console.WriteLine(obj.GetType().Name); // "Lib.PrivateType"
According to the test result, even cast private type as dynamic, I still can get the private type information from GetType(), why DapperRow.GetType() return null?

DapperRow is specifically built and utilized within Dapper to provide highly optimized row returns without reiterating header information. This is to help condense the size of the object and reduce redundant data, making it more efficient.
However, it would appear that the StackExchange team took the meta programming even further than a first glance would indicate.
DapperRow implements the System.Dynamic.IDynamicMetaObjectProvide interface, which requires that the GetMetaObject method be implemented:
System.Dynamic.DynamicMetaObject System.Dynamic.IDynamicMetaObjectProvider.GetMetaObject(
System.Linq.Expressions.Expression parameter)
{
return new DapperRowMetaObject(parameter,
System.Dynamic.BindingRestrictions.Empty, this);
}
DapperRowMetaObject is a custom implementation of DynamicMetaObject that essentially hijacks and overrides what methods can be invoked against the dynamic type and what those calls should translate to. In this case, calls to anything other than the DapperRow's IDictionary.Item getter or the DapperRow.SetValue will fail since they are always routed to those two calls, but the value will be defaulted to null for any "get" calls where the target property does not exist in the table.
public bool TryGetValue(string name, out object value)
{
var index = table.IndexOfName(name);
if (index < 0)
{ // doesn't exist
value = null;
return false;
}
...
}
At that point, any methods invoked on a null dynamic value will throw a RuntimeBinderException:
RuntimeBinderException: Cannot perform runtime binding on a null
reference
You can easily test this hypothesis by replacing GetType() with another call that will throw the exact same exception:
var rec = cn.Query("select getdate() as D").Single();
var t = rec.AsEnumerable();
Console.WriteLine(t.ToList());
Keep in mind, the underlying type information of any properties on the dynamic object itself can still be accessed directly:
var rec = cn.Query("select getdate() as D").Single();
var t = rec.D.GetType();
Console.WriteLine(t.Name);

C# list in function param

I'm new to C#. I want to take a list as argument and return another from the data I get from the first one.
private List<DestinationGenericMapProps> ConstructDestinationMapPropsList(List<BoutiqueInWebService> datas)
{
var result = new List<DestinationGenericMapProps>(datas);
return result;
}
I get this error:
Error 241 The best overloaded method match for System.Collections.Generic.List<VDDataUpdaterGeneric.DataObjects.DestinationGenericMapProps>.List(int) has some invalid arguments
I know this is probably pretty basic but I'm new to C# and struggle with this. Thanks for your help.

List<BoutiqueInWebService> is not a List<DestinationGenericMapProps>.
This will not work unless BoutiqueInWebService is derived from DestinationGenericMapProps.
Basically, there is a List<T>(IEnumerable<T>) constructor, but the T's have to be the same.
Either change your return type to List<BoutiqueInWebService> and change your new statement:
private List<BoutiqueInWebService> ConstructDestinationMapPropsList(List<BoutiqueInWebService> datas)
{
var result = new List<BoutiqueInWebService>(datas);
return result;
}
or change your parameter to be of type List<DestinationGenericMapProps>:
private List<DestinationGenericMapProps> ConstructDestinationMapPropsList(List<DestinationGenericMapProps> datas)
{
var result = new List<DestinationGenericMapProps>(datas);
return result;
}
Alternatively, if you know how to make a DestinationGenericMapProps from a BoutiqueInWebService, you can use System.Linq and perform a select against the argument:
private List<DestinationGenericMapProps> ConstructDestinationMapPropsList(List<BoutiqueInWebService> datas)
{
var result = datas.Select(x => new DestinationGenericMapProps() { ... }).ToList();
return result;
}

Your method return type is a list of DestinationGenericMapProps, but you're trying to create list of BoutiqueInWebService (which is data).
You can do this to match your return type:
private List<DestinationGenericMapProps>
ConstructDestinationMapPropsList(List<BoutiqueInWebService> datas)
{
return (from d in datas
select new DestinationGenericMapProps()
{
// map properties here
Prop1 = d.SomePropInData
}).ToList();
}

You're getting the error because you're trying to populate a list of one type (DestinationGenericMapProps) with objects from a list of a different type (BoutiqueInWebService) which isn't type safe.
You can only do this if BoutiqueInWebService inherits from DestinationGenericMapProps.

C# supports function overloading, which means that a class can have more than one function with the same name as long as the parameters are different. The compiler decides which overload to call by compairing the types of the parameters. This applies to constructors too.
The List class has a three overloads of its constuctor:
List<T>()
List<T>(IEnumerable<T>)
List<T>(int)
I assume that you are trying to use the second of those as it will create a new list from the passed in one. For the list you are creating T is a DestinationGenericMapProps. So the constructors are:
List<DestinationGenericMapProps>()
List<DestinationGenericMapProps>(IEnumerable<DestinationGenericMapProps>)
List<DestinationGenericMapProps>(int)
The list you have passed in has T set to BoutiqueInWebService. As such the compiler is trying to find a constructor like this in the list above.
List<DestinationGenericMapProps>(IEnumerable<BoutiqueInWebService>)
As it can't find one it raises the error you have recieved.
Is it possible to cast a BoutiqueInWebService to a DestinationGenericMapProps object? If so you could do this:
var result = datas.Cast<DestinationGenericMapProps>().ToList()
If no direct cast is possible it may be possible to do a long hand cast like this:
var result = datas.Select(o => new DestinationGenericMapProps() { PropA = o.PropA, PropB = o.PropB /* etc */}).ToList();

c# Asp.net Error :Specified cast is not valid

Here is a portion of a code ..
public Admin_GetCourseById_spResult GetCourseById(long? courseId, short languageId)
{
ISQUserDataContext db = CreateDataContext();
Admin_GetCourseById_spResult result;
result = db.Admin_GetCourseById_sp(courseId,false,languageId).FirstOrDefault();
return result;
}
the third line in the function throws error Specified cast is not valid.
Any clue about whats happening ??

Small rewrite (needs more work)
public Course GetCourseById(long? courseId, short languageId)
{
ISQUserDataContext db = CreateDataContext();
return new Course(db.Admin_GetCourseById_sp(courseId, false, languageId).FirstOrDefault());
}
and then add a class Course with a constructor accepting the returntype of Admin_GetCourseById_sp to build a nice Course object.

Your
db.Admin_GetCourseById_sp(courseId,false,languageId).FirstOrDefault() line returns a datarow.
(It might return null if there are no data)
Therefore what you can do is this,
you can set each attribute of your
Admin_GetCourseById_spResult result object with the matching value from the returned datarow
i.e result.courseId = row["course_id"].ToString()
{ I assumed that courseId is String in your Admin_GetCourseById_spResult class + the matching db column is course_id.
You have given little data, so could answer only like this. Good Luck !

Entity framework with Linq

I have following method. I need to return var tynames by method so what would be the return type of the method will it be List<string> or something else and also what is the use of FirstOrDefault().
Thanks in advance for your reply
public static List<string> AppType()
{
var context = new Dll_IssueTracking.IssuTrackingEntities();// Object context defined in Dll_IssuTracking DLL
var query = from c in context.ApplicationTypes//Query to find TypeNames
select new { c.TypeName };
var **TypeNames** = query.FirstOrDefault();
}

FirstOrDefault returns the first element found, or the default value (which is null in this case) if the query returned no results.
In this case the return value of the method should be ApplicationType:
public static ApplicationType AppType()
{
var context = new Dll_IssueTracking.IssuTrackingEntities(); // Object context defined in Dll_IssuTracking DLL
var query = from c in context.ApplicationTypes //Query to find TypeNames
select new { c.TypeName };
return query.FirstOrDefault();
}

FirstOrDefault return first element in sequence, in this sample ApplicationTypes is your sequence or a default value if the sequence contains no elements.

FirstOrDefault is an extension method which looks something like this:
public T FirstOrDefault>T>(this IEnumerable<T> query)
{
return query.Any() ? query.First() : default(T);
}
So, it returns the first element in the sequence if it is not empty, or the default of the type if the sequence is empty.
For Instance, if you have an Enumerable<LinqEntity>, then most likely default(LinqEntity) is null. If you had something like Enumerable<int> then default(int) is 0.