Pfthb

I have a class like this:

public class Student

 public int Id get; set; 
 public string Name get; set; 
 public string LOANIDBPM get; set; 
 public string REPORTTYPE get; set; 

I have a list Students,
I want to filter some student in list by LOANIDBPM and REPORTTYPE.

Usually, this is the code (using linq)

public void GetListStudent(List<Student> listStudent)

 listStudent = listStudent.Where(x => x.LOANIDBPM == "MIKEN" && x.REPORTTYPE == "DX").ToList();

However, for some reason, i can't Explicit "List",
My solution is below:

public void GetListStudent(object listStudent)

 ParameterExpression param = Expression.Parameter(listStudent.First().GetType(), nameof(listStudent));
 Expression propLoanBPM = Expression.Property(param, "LOANIDBPM");
 Expression<Func<string>> loanIdLampda = () => "MIKEN";
 Expression searchLoanBPM = Expression.Equal(propLoanBPM, loanIdLampda.Body);

 Expression propReportType = Expression.Property(param, "REPORTTYPE");
 Expression<Func<string>> reportTypeLampda = () => "DX";

 Expression searchReportType = Expression.Equal(propReportType, reportTypeLampda.Body);

 Expression searchFinal = Expression.And(searchLoanBPM, searchReportType);


 Expression<Func<???, bool>> lampda = Expression.Lambda<Func<???, bool>>(searchFinal, param);

 listStudent = listStudent.Where(lampda).ToArray();

The code above has two problems:

1: I don't know type of Student in Expression Func,
I can't use like:

Expression<Func< listStudent.First().GetType(), bool>> lampda = Expression.Lambda<Func< listStudent.First().GetType(), bool>>(searchFinal, param);

2: In Where method, it's need to IQueryable, but in my code is Expression Func.

Sorry by my English.
Thank you so much

Your first example doesn't compile because listStudent is a list and LINQ is generally going to return an IEnumerable of some kind. You need to add ToList():

public void GetListStudent(List<Student> listStudent)

 listStudent = listStudent
 .Where
 (
 x => x.LOANIDBPM == "MIKEN" && x.REPORTTYPE == "DX"
 )
 .ToList(); //<-- add this

Your second example doesn't work because c# doesn't know that your object array is actually a list of students. You can tell it using the Cast<>() method. When you're done, you need to convert back to an array, so add ToArray() at the end.

public void GetListStudent(object listStudent)

 listStudent = listStudent
 .Cast<Student>() //<-- add this
 .Where
 (
 x => x.LOANIDBPM == "MIKEN" && x.REPORTTYPE == "DX"
 )
 .ToArray(); //<-- and this

If only some of the objects are known to be students, you can use OfType<>() to filter them out.

public void GetListStudent(object listStudent)

 listStudent = listStudent
 .OfType<Student>() //<-- add this
 .Where
 (
 x => x.LOANIDBPM == "MIKEN" && x.REPORTTYPE == "DX"
 )
 .ToArray(); //<-- and this

And if you have absolutely no clue what those objects are but are quite certain they have LOANIDBPM and REPORTTYPE properties, I suppose you could use dynamic:

public void GetListStudent(List<dynamic> listStudent)

 listStudent = listStudent
 .Where
 (
 x => x.LOANIDBPM == "MIKEN" && x.REPORTTYPE == "DX"
 )
 .ToList();