How to select column from string in efcore?

How to select column from string in efcore? - c#

I am looking for a solution to select a single column based on the column name. The type of columns I want to select is always string. Like so:
_dbContext.MyModel.Select("Name")...
I wanted to create a extension method:
_dbContext.MyModel.SelectFromString("Name")
It should allow nested selects, like:
_dbContext.MyModel.SelectFromString("Child.Name")
Extension method:
public static IQueryable<T> SelectFromString<T>(this IQueryable<T> query, string column)
{
var parameter = Expression.Parameter(typeof(T));
var property = Expression.Property(parameter, column);
//...
return query.Select(lambda);
}
Not sure how to create the lambda. Any ideas?

The following method projects any property to string and returns IQueryable<string>. Nested properties also supported.
public static class QueryableExtensions
{
public static IQueryable<string> SelectFromString<T>(this IQueryable<T> query, string column)
{
var parameter = Expression.Parameter(typeof(T), "e");
var property = MakePropPath(parameter, column);
if (property.Type != typeof(string))
{
if (property.Type != typeof(object))
property = Expression.Convert(property, typeof(object));
property = Expression.Call(_toStringMethod, property);
}
var lambda = Expression.Lambda<Func<T, string>>(property, parameter);
return query.Select(lambda);
}
private static Expression MakePropPath(Expression objExpression, string path)
{
return path.Split('.').Aggregate(objExpression, Expression.PropertyOrField);
}
private static MethodInfo _toStringMethod = typeof(Convert).GetMethods()
.Single(m =>
m.Name == nameof(Convert.ToString) && m.GetParameters().Length == 1 &&
m.GetParameters()[0].ParameterType == typeof(object)
);
}

Related

LINQ method, which Dynamically ordering data by column name I send

What I want to do?
I want to create method, which Dynamically ordering data by column name I send.
First I created a project for testing. I see the project works super.
Test Project:
PropertyInfo pinfo = typeof(MockData).GetProperty(orderColumn);
switch (orderDirection)
{
case "asc":
mockDataList = q.OrderBy(o => pinfo.GetValue(o, null)).Skip(start).Take(length).ToList();
break;
case "desc":
mockDataList = q.OrderByDescending(o => pinfo.GetValue(o, null)).Skip(start).Take(length).ToList();
break;
}
After, I applied things, which I learned to my essential project that way:
Essential Project:
public IQueryable<T> RefactoringQuerybyPagination<T>(DataTablesRequestModel dataTablesRequestModel, IQueryable<T> query)
{
PropertyInfo pinfo = typeof(T).GetProperty(dataTablesRequestModel.OrderColumn);
switch (dataTablesRequestModel.OrderDirection)
{
case "asc":
query = query.OrderBy(o => pinfo.GetValue(o, null) != null).ThenBy(o => pinfo.GetValue(o, null));
break;
case "desc":
query = query.OrderByDescending(o => pinfo.GetValue(o, null) != null).ThenBy(o => pinfo.GetValue(o, null));
break;
}
query = query.Skip(dataTablesRequestModel.Start);
query = query.Take(dataTablesRequestModel.Length);
var test = query.ToList();
return query;
}
But it doesn't work and it gives me an error ("could not be translated...")
Solution I tried
public static IQueryable<T> OrderBy<T>(this IQueryable<T> items, string propertyName)
{
var typeOfT = typeof(T);
var parameter = Expression.Parameter(typeOfT, "parameter");
var propertyType = typeOfT.GetProperty(propertyName).PropertyType;
var propertyAccess = Expression.PropertyOrField(parameter, propertyName);
var orderExpression = Expression.Lambda(propertyAccess, parameter);
var expression = Expression.Call(typeof(Queryable), "OrderBy", new Type[] { typeOfT, propertyType }, items.Expression, Expression.Quote(orderExpression));
return items.Provider.CreateQuery<T>(expression);
}
It works but I can't manipulate expression. (like o = > o.Column.HasValue).
All day, I worked on this, I'm really tired. Can anyone help me?

Try to create a QueryableExtensions with the the following code:
//required using System.Linq;
//required using System.Linq.Expressions;
public static class QueryableExtensions
{
public static IQueryable<T> OrderBy<T>(this IQueryable<T> source, string columnName, bool isAscending = true)
{
if (String.IsNullOrEmpty(columnName))
{
return source;
}
ParameterExpression parameter = Expression.Parameter(source.ElementType, "");
MemberExpression property = Expression.Property(parameter, columnName);
LambdaExpression lambda = Expression.Lambda(property, parameter);
string methodName = isAscending ? "OrderBy" : "OrderByDescending";
Expression methodCallExpression = Expression.Call(typeof(Queryable), methodName,
new Type[] { source.ElementType, property.Type },
source.Expression, Expression.Quote(lambda));
return source.Provider.CreateQuery<T>(methodCallExpression);
}
Then, in the LINQ statement, we could use the above method to sort the records:
public IActionResult CategoryIndex()
{
//CategoryName Descending
var result1 = _context.Categories.OrderBy("CategoryName", false).Select(c=>c.CategoryName).ToArray();
//CategoryID Descending
var result2 = _context.Categories.OrderBy("CategoryID", false).Select(c => c.CategoryID).ToArray();
return View();
}
The screenshot as below:

You can use the Dynamic LINQ to achieve what you are trying to do in a lot easier and simplified way. You can find the NuGet package here - System.Linq.Dynamic.Core
From your code I'm assuming your scenario does not involve sorting/ordering on multiple columns. If so, you can create an extension method like below -
// you'll need to add this
// using System.Linq.Dynamic.Core;
public static class IQueryableExtension
{
public static IQueryable<T> ApplyOrder<T>(this IQueryable<T> source, string column, string direction)
{
if (string.IsNullOrWhiteSpace(column))
return source;
var pinfo = typeof(T).GetProperty(column);
if (pinfo == null)
return source;
var order = (direction == "desc") ? $"{column} desc" : column;
return source.OrderBy(order);
}
}
You can use it from your existing code like -
public IQueryable<T> RefactoringQuerybyPagination<T>(DataTablesRequestModel dataTablesRequestModel, IQueryable<T> query)
{
// here is the call
query = query.ApplyOrder(dataTablesRequestModel.OrderColumn, dataTablesRequestModel.OrderDirection);
query = query.Skip(dataTablesRequestModel.Start);
query = query.Take(dataTablesRequestModel.Length);
var test = query.ToList();
return query;
}

Linq orderbys from collection [duplicate]

This question already has answers here:
Dynamic LINQ OrderBy on IEnumerable<T> / IQueryable<T>
(24 answers)
Closed 2 years ago.
How do I specify the argument passed to orderby using a value I take as a parameter?
Ex:
List<Student> existingStudends = new List<Student>{ new Student {...}, new Student {...}}
Currently implementation:
List<Student> orderbyAddress = existingStudends.OrderBy(c => c.Address).ToList();
Instead of c.Address, how can I take that as a parameter?
Example
string param = "City";
List<Student> orderbyAddress = existingStudends.OrderByDescending(c => param).ToList();

You can use a little bit of reflection to construct the expression tree as follows (this is an extension method):
public static IQueryable<TEntity> OrderBy<TEntity>(this IQueryable<TEntity> source, string orderByProperty,
bool desc)
{
string command = desc ? "OrderByDescending" : "OrderBy";
var type = typeof(TEntity);
var property = type.GetProperty(orderByProperty);
var parameter = Expression.Parameter(type, "p");
var propertyAccess = Expression.MakeMemberAccess(parameter, property);
var orderByExpression = Expression.Lambda(propertyAccess, parameter);
var resultExpression = Expression.Call(typeof(Queryable), command, new Type[] { type, property.PropertyType },
source.Expression, Expression.Quote(orderByExpression));
return source.Provider.CreateQuery<TEntity>(resultExpression);
}
orderByProperty is the Property name you want to order by and if pass true as parameter for desc, will sort in descending order; otherwise, will sort in ascending order.
Now you should be able to do existingStudents.OrderBy("City",true); or existingStudents.OrderBy("City",false);

Here's a possiblity using reflection...
var param = "Address";
var propertyInfo = typeof(Student).GetProperty(param);
var orderByAddress = items.OrderBy(x => propertyInfo.GetValue(x, null));

To expand on the answer by #Icarus: if you want the return type of the extension method to be an IOrderedQueryable instead of an IQueryable, you can simply cast the result as follows:
public static IOrderedQueryable<TEntity> OrderBy<TEntity>(this IQueryable<TEntity> source, string orderByProperty, bool desc)
{
string command = desc ? "OrderByDescending" : "OrderBy";
var type = typeof(TEntity);
var property = type.GetProperty(orderByProperty);
var parameter = Expression.Parameter(type, "p");
var propertyAccess = Expression.MakeMemberAccess(parameter, property);
var orderByExpression = Expression.Lambda(propertyAccess, parameter);
var resultExpression = Expression.Call(typeof(Queryable), command, new Type[] { type, property.PropertyType },
source.Expression, Expression.Quote(orderByExpression));
return (IOrderedQueryable<TEntity>)source.Provider.CreateQuery<TEntity>(resultExpression);
}

1) Install System.Linq.Dynamic
2) Add the following code
public static class OrderUtils
{
public static string ToStringForOrdering<T, TKey>(this Expression<Func<T, TKey>> expression, bool isDesc = false)
{
var str = expression.Body.ToString();
var param = expression.Parameters.First().Name;
str = str.Replace("Convert(", "(").Replace(param + ".", "");
return str + (isDesc ? " descending" : "");
}
}
3) Write your switch for selecting of Lambda function
public static class SortHelper
{
public static Expression<Func<UserApp, object>> UserApp(string orderProperty)
{
orderProperty = orderProperty?.ToLowerInvariant();
switch (orderProperty)
{
case "firstname":
return x => x.PersonalInfo.FirstName;
case "lastname":
return x => x.PersonalInfo.LastName;
case "fullname":
return x => x.PersonalInfo.FirstName + x.PersonalInfo.LastName;
case "email":
return x => x.Email;
}
}
}
4) Use your helpers
Dbset.OrderBy(SortHelper.UserApp("firstname").ToStringForOrdering())
5) You can use it with pagging (PagedList)
public virtual IPagedList<T> GetPage<TOrder>(Page page, Expression<Func<T, bool>> where, Expression<Func<T, TOrder>> order, bool isDesc = false,
params Expression<Func<T, object>>[] includes)
{
var orderedQueryable = Dbset.OrderBy(order.ToStringForOrdering(isDesc));
var query = orderedQueryable.Where(where).GetPage(page);
query = AppendIncludes(query, includes);
var results = query.ToList();
var total = Dbset.Count(where);
return new StaticPagedList<T>(results, page.PageNumber, page.PageSize, total);
}
Explanation
System.Linq.Dynamic allows us to set string value in OrderBy method. But inside this extension the string will be parsed to Lambda. So I thought it would work if we will parse Lambda to string and give it to OrderBy method. And it works!

Here's something I came up with for dealing with a conditional Descending. You could combine this with other methods of generating the keySelector func dynamically.
public static IOrderedQueryable<TSource> OrderBy<TSource, TKey>(this IQueryable<TSource> source,
System.Linq.Expressions.Expression<Func<TSource, TKey>> keySelector,
System.ComponentModel.ListSortDirection sortOrder
)
{
if (sortOrder == System.ComponentModel.ListSortDirection.Ascending)
return source.OrderBy(keySelector);
else
return source.OrderByDescending(keySelector);
}
Usage:
//imagine this is some parameter
var direction = System.ComponentModel.ListSortDirection.Ascending;
query = query.OrderBy(ec => ec.MyColumnName, direction);
Notice this allows you to chain this .OrderBy extension with a new parameter onto any IQueryable.
// perhaps passed in as a request of user to change sort order
// var direction = System.ComponentModel.ListSortDirection.Ascending;
query = context.Orders
.Where(o => o.Status == OrderStatus.Paid)
.OrderBy(ec => ec.OrderPaidUtc, direction);

private Func<T, object> GetOrderByExpression<T>(string sortColumn)
{
Func<T, object> orderByExpr = null;
if (!String.IsNullOrEmpty(sortColumn))
{
Type sponsorResultType = typeof(T);
if (sponsorResultType.GetProperties().Any(prop => prop.Name == sortColumn))
{
System.Reflection.PropertyInfo pinfo = sponsorResultType.GetProperty(sortColumn);
orderByExpr = (data => pinfo.GetValue(data, null));
}
}
return orderByExpr;
}
public List<T> OrderByDir<T>(IEnumerable<T> source, string dir, Func<T, object> OrderByColumn)
{
return dir.ToUpper() == "ASC" ? source.OrderBy(OrderByColumn).ToList() : source.OrderByDescending(OrderByColumn).ToList();``
}
// Call the code like below
var orderByExpression= GetOrderByExpression<SearchResultsType>(sort);
var data = OrderByDir<SponsorSearchResults>(resultRecords, SortDirectionString, orderByExpression);

This doesn't let you pass a string, as you asked for in your question, but it might still work for you.
The OrderByDescending method takes a Func<TSource, TKey>, so you can rewrite your function this way:
List<Student> QueryStudents<TKey>(Func<Student, TKey> orderBy)
{
return existingStudents.OrderByDescending(orderBy).ToList();
}
There are other overloads for OrderByDescending as well that take a Expression<Func<TSource, TKey>>, and/or a IComparer<TKey>. You could also look into those and see if they provide you anything of use.

The only solution that worked for me was posted here https://gist.github.com/neoGeneva/1878868 by neoGeneva.
I will re-post his code because it works well and I wouldn't want it to be lost in the interwebs!
public static IQueryable<T> OrderBy<T>(this IQueryable<T> source, string sortExpression)
{
if (source == null)
throw new ArgumentNullException("source", "source is null.");
if (string.IsNullOrEmpty(sortExpression))
throw new ArgumentException("sortExpression is null or empty.", "sortExpression");
var parts = sortExpression.Split(' ');
var isDescending = false;
var propertyName = "";
var tType = typeof(T);
if (parts.Length > 0 && parts[0] != "")
{
propertyName = parts[0];
if (parts.Length > 1)
{
isDescending = parts[1].ToLower().Contains("esc");
}
PropertyInfo prop = tType.GetProperty(propertyName);
if (prop == null)
{
throw new ArgumentException(string.Format("No property '{0}' on type '{1}'", propertyName, tType.Name));
}
var funcType = typeof(Func<,>)
.MakeGenericType(tType, prop.PropertyType);
var lambdaBuilder = typeof(Expression)
.GetMethods()
.First(x => x.Name == "Lambda" && x.ContainsGenericParameters && x.GetParameters().Length == 2)
.MakeGenericMethod(funcType);
var parameter = Expression.Parameter(tType);
var propExpress = Expression.Property(parameter, prop);
var sortLambda = lambdaBuilder
.Invoke(null, new object[] { propExpress, new ParameterExpression[] { parameter } });
var sorter = typeof(Queryable)
.GetMethods()
.FirstOrDefault(x => x.Name == (isDescending ? "OrderByDescending" : "OrderBy") && x.GetParameters().Length == 2)
.MakeGenericMethod(new[] { tType, prop.PropertyType });
return (IQueryable<T>)sorter
.Invoke(null, new object[] { source, sortLambda });
}
return source;
}

Add the nugget package Dynamite to your code
Add the namespace Dynamite.Extensions
Eg : using Dynamite.Extensions;
Give Order by query like any SQL query
Eg : students.OrderBy(" City DESC, Address").ToList();

To extend the response of #Icarus: if you want to sort by two fields I could perform the following function (for one field the response of Icarius works very well).
public static IQueryable<T> OrderByDynamic<T>(this IQueryable<T> q, string SortField1, string SortField2, bool Ascending)
{
var param = Expression.Parameter(typeof(T), "p");
var body = GetBodyExp(SortField1, SortField2, param);
var exp = Expression.Lambda(body, param);
string method = Ascending ? "OrderBy" : "OrderByDescending";
Type[] types = new Type[] { q.ElementType, exp.Body.Type };
var mce = Expression.Call(typeof(Queryable), method, types, q.Expression, exp);
return q.Provider.CreateQuery<T>(mce);
}
This is the function that the body returns for the lambda expression, it works with string and int, but it is enough to add more types to make it work according to the need of each programmer
public static NewExpression GetBodyExp(string field1, string field2, ParameterExpression Parametro)
{
// SE OBTIENE LOS NOMBRES DE LOS TIPOS DE VARIABLE
string TypeName1 = Expression.Property(Parametro, field1).Type.Name;
string TypeName2 = Expression.Property(Parametro, field2).Type.Name;
// SE DECLARA EL TIPO ANONIMO SEGUN LOS TIPOS DE VARIABLES
Type TypeAnonymous = null;
if (TypeName1 == "String")
{
string var1 = "0";
if (TypeName2 == "Int32")
{
int var2 = 0;
var example = new { var1, var2 };
TypeAnonymous = example.GetType();
}
if (TypeName2 == "String")
{
string var2 = "0";
var example = new { var1, var2 };
TypeAnonymous = example.GetType();
}
}
if (TypeName1 == "Int32")
{
int var1 = 0;
if (TypeName2 == "Int32")
{
string var2 = "0";
var example = new { var1, var2 };
TypeAnonymous = example.GetType();
}
if (TypeName2 == "String")
{
string var2 = "0";
var example = new { var1, var2 };
TypeAnonymous = example.GetType();
}
}
//se declaran los TIPOS NECESARIOS PARA GENERAR EL BODY DE LA EXPRESION LAMBDA
MemberExpression[] args = new[] { Expression.PropertyOrField(Parametro, field1), Expression.PropertyOrField(Parametro, field2) };
ConstructorInfo CInfo = TypeAnonymous.GetConstructors()[0];
IEnumerable<MemberInfo> a = TypeAnonymous.GetMembers().Where(m => m.MemberType == MemberTypes.Property);
//BODY
NewExpression body = Expression.New(CInfo, args, TypeAnonymous.GetMembers().Where(m => m.MemberType == MemberTypes.Property));
return body;
}
to use it the following is done
IQueryable<MyClass> IqMyClass= context.MyClass.AsQueryable();
List<MyClass> ListMyClass= IqMyClass.OrderByDynamic("UserName", "IdMyClass", true).ToList();
if there is a better way to do this, it would be great if they share it
I managed to solve it thanks to: How can I make a Multiple property lambda expression with Linq

New Answer : this is a more complete answer that supports multiple columns for order by like SQL. Example : .OrderBy("FirstName,Age DESC") :
namespace Utility;
public static class QueryExtension
{
public static IQueryable<TEntity> OrderBy<TEntity>(this IQueryable<TEntity> source, string orderByProperty, bool desc, bool isThenBy = false)
{
string command = isThenBy ? (desc ? "ThenByDescending" : "ThenBy") : (desc ? "OrderByDescending" : "OrderBy");
var type = typeof(TEntity);
var property = type.GetProperty(orderByProperty);
var parameter = Expression.Parameter(type, "p");
var propertyAccess = Expression.MakeMemberAccess(parameter, property);
var orderByExpression = Expression.Lambda(propertyAccess, parameter);
var resultExpression = Expression.Call(typeof(Queryable), command, new Type[] { type, property.PropertyType },
source.Expression, Expression.Quote(orderByExpression));
return source.Provider.CreateQuery<TEntity>(resultExpression);
}
public static IQueryable<TEntity> OrderBy<TEntity>(this IQueryable<TEntity> source, string sqlOrderByList)
{
var ordebyItems = sqlOrderByList.Trim().Split(',');
IQueryable<TEntity> result = source;
bool useThenBy = false;
foreach (var item in ordebyItems)
{
var splt = item.Trim().Split(' ');
result = result.OrderBy(splt[0].Trim(), (splt.Length > 1 && splt[1].Trim().ToLower() == "desc"), useThenBy);
if (useThenBy)
useThenBy = true;
}
return result;
}
}
The second function iterates over orderby columns and uses the first one.
Use it like this :
using Utility;
...
public void MyMethod()
{
var query = _dbContext.Person.AsQueryable();
query.OrderBy("FirstName,Age DESC");
}

I'm way late to the party but none of these solutions worked for me. I was eager to try System.Linq.Dynamic, but I couldn't find that on Nuget, maybe depreciated? Either way...
Here is a solutions I came up with. I needed to dynamically use a mixture of OrderBy, OrderByDescending and OrderBy > ThenBy.
I simply created an extension method for my list object, a bit hacky I know... I wouldn't recommend this if it were something I was doing a lot of, but it's good for a one off.
List<Employee> Employees = GetAllEmployees();
foreach(Employee oEmployee in Employees.ApplyDynamicSort(eEmployeeSort))
{
//do stuff
}
public static IOrderedEnumerable<Employee> ApplyDynamicSort(this List<Employee> lEmployees, Enums.EmployeeSort eEmployeeSort)
{
switch (eEmployeeSort)
{
case Enums.EmployeeSort.Name_ASC:
return lEmployees.OrderBy(x => x.Name);
case Enums.EmployeeSort.Name_DESC:
return lEmployees.OrderByDescending(x => x.Name);
case Enums.EmployeeSort.Department_ASC_Salary_DESC:
return lEmployees.OrderBy(x => x.Department).ThenByDescending(y => y.Salary);
default:
return lEmployees.OrderBy(x => x.Name);
}
}

Better way to Sort a List by any property

My method receives all DataTables parameters to sort table by column clicked. I call this method from controller of each page list.
I'm looking for a better way to do this like a generic method for all types: string, int, decimal, double, bool (nullable or not). But I can't find it.
My current code:
public List<T> OrderingList<T>(List<T> list, DataTablesParam model)
{
var iColumn = model.Order.FirstOrDefault().Column;
var property = typeof(T).GetProperty(model.Columns.ToArray()[iColumn].Data);
var param = Expression.Parameter(typeof(T));
var final = Expression.Property(param, property);
var isDirAsc = model.Order.FirstOrDefault().Dir.Equals("asc");
if (property.PropertyType == typeof(string))
{
var lambda = Expression.Lambda<Func<T, string>>(final, param).Compile();
return isDirAsc ? list.OrderBy(lambda).ToList() : list.OrderByDescending(lambda).ToList();
}
else if (property.PropertyType == typeof(int))
{
var lambda = Expression.Lambda<Func<T, int>>(final, param).Compile();
return isDirAsc ? list.OrderBy(lambda).ToList() : list.OrderByDescending(lambda).ToList();
}
else if (property.PropertyType == typeof(bool))
{
var lambda = Expression.Lambda<Func<T, bool>>(final, param).Compile();
return isDirAsc ? list.OrderBy(lambda).ToList() : list.OrderByDescending(lambda).ToList();
}
else if (property.PropertyType == typeof(decimal))
{
var lambda = Expression.Lambda<Func<T, decimal>>(final, param).Compile();
return isDirAsc ? list.OrderBy(lambda).ToList() : list.OrderByDescending(lambda).ToList();
}
else if (property.PropertyType == typeof(double))
{
var lambda = Expression.Lambda<Func<T, double>>(final, param).Compile();
return isDirAsc ? list.OrderBy(lambda).ToList() : list.OrderByDescending(lambda).ToList();
}
return list;
}
I want to do something like this: (But this code doesn't work)
public List<T> OrderingList<T>(List<T> list, DataTablesParam model)
{
var iColumn = model.Order.FirstOrDefault().Column;
var property = typeof(T).GetProperty(model.Columns.ToArray()[iColumn].Data);
var param = Expression.Parameter(typeof(T));
var final = Expression.Property(param, property);
var isDirAsc = model.Order.FirstOrDefault().Dir.Equals("asc");
var lambda = Expression.Lambda<Func<T, dynamic>>(final, param).Compile();
return isDirAsc ? list.OrderBy(lambda).ToList() : list.OrderByDescending(lambda).ToList();
}

You can just call the Enumerable.OrderBy method using reflection. That way, you don’t have to know the type at compile-time. To do that, you just need to get the method, and create a generic method using the property’s type:
private IEnumerable<T> Sort<T> (List<T> list, string propertyName)
{
MethodInfo orderByMethod = typeof(Enumerable).GetMethods().First(mi => mi.Name == "OrderBy" && mi.GetParameters().Length == 2);
PropertyInfo pi = typeof(T).GetProperty(propertyName);
MethodInfo orderBy = orderByMethod.MakeGenericMethod(typeof(T), pi.PropertyType);
ParameterExpression param = Expression.Parameter(typeof(T));
Delegate accessor = Expression.Lambda(Expression.Property(param, pi), param).Compile();
return (IEnumerable<T>)orderBy.Invoke(null, new object[] { lst, accessor });
}
Note that I abstracted out the stuff about your model to keep this method generic enough. It can basically sort by any property on a list by just specifying the property name. Your original method would then look like this:
public List<T> OrderingList<T>(List<T> list, DataTablesParam model)
{
var iColumn = model.Order.FirstOrDefault().Column;
string propertyName = model.Columns.ToArray()[iColumn].Data;
return Sort(list, propertyName).ToList();
}

It's works fine for me: (Thanks #Poke)
https://stackoverflow.com/a/31393168/5112444
My final method:
private IEnumerable<T> Sort<T>(IEnumerable<T> list, string propertyName, bool isAsc)
{
MethodInfo orderByMethod = typeof(Enumerable).GetMethods().First(mi => mi.Name == (isAsc ? "OrderBy" : "OrderByDescending") && mi.GetParameters().Length == 2);
PropertyInfo pi = typeof(T).GetProperty(propertyName);
MethodInfo orderBy = orderByMethod.MakeGenericMethod(typeof(T), pi.PropertyType);
ParameterExpression param = Expression.Parameter(typeof(T));
Delegate accessor = Expression.Lambda(Expression.Call(param, pi.GetGetMethod()), param).Compile();
return (IEnumerable<T>)orderBy.Invoke(null, new object[] { list, accessor });
}

Your suggested method almost works. You need to change two things in order to make it work:
public List<T> OrderingList<T>(List<T> list, DataTablesParam model)
{
var iColumn = model.Order.FirstOrDefault().Column;
var property = typeof(T).GetProperty(model.Columns.ToArray()[iColumn].Data);
var param = Expression.Parameter(typeof(T), "p");
Expression final = Expression.Property(param, property);
// Boxing of value types
if (property.PropertyType.IsValueType) {
final = Expression.MakeUnary(ExpressionType.Convert, final, typeof(object));
}
var isDirAsc = model.Order.FirstOrDefault().Dir.Equals("asc");
// VVVVVV
var lambda = Expression.Lambda<Func<T, object>>(final, param).Compile();
return isDirAsc
? list.OrderBy(lambda).ToList()
: list.OrderByDescending(lambda).ToList();
}
Instead of using dynamic use object, since every type is an object.
If you have a value type, you need a boxing operation, i.e. you must cast the value to object (object)i. This is done with a unary convert operation:
Expression final = Expression.Property(param, property);
if (property.PropertyType.IsValueType) {
final = Expression.MakeUnary(ExpressionType.Convert, final, typeof(object));
}
Note also that final is declared explicitly as Expression, since the expression type might change from property to unary expression.

Beyond just not being very generic, your solution also requires a lot of extra memory because you're copying the list with LINQ. You can avoid this using List.Sort.
I would do:
static void SortBy<T>(List<T> list, MemberInfo member, bool desc)
{
Comparison<T> cmp = BuildComparer<T>(member, desc);
list.Sort(cmp);
}
static Comparison<T> BuildComparer<T>(MemberInfo member, bool desc)
{
var left = Expression.Parameter(typeof(T));
var right = Expression.Parameter(typeof(T));
Expression cmp = Expression.Call(
Expression.MakeMemberAccess(desc ? right : left, member),
"CompareTo",
Type.EmptyTypes,
Expression.MakeMemberAccess(desc ? left : right, member));
return Expression.Lambda<Comparison<T>>(cmp, left, right).Compile();
}

I found a better way to do this. I had to do 3 steps:
1 - Add the package "Linq Dynamic" in project:
Install-Package System.Linq.Dynamic.Library
2 - Import the package in Class:
using System.Linq.Dynamic;
3 - Order list by the string name of property:
list.OrderBy(stringPropertyName); //asc
list.OrderBy(stringPropertyName + " descending"); //des
It work perfectly for me.

Using reflection to obtain values based on a specific query condition

I have a slightly different issue to the one answered here (Using reflection to retrieve a value from a list)
While the approved answer here works fine for select, I'd like to extend it so that I can obtain data from a query based on a condition type. Currently, my adapted code looks like this
public static async Task<T> GetDataFromTable<T>(string paramName, string condition="")
{
var k = Activator.CreateInstance(typeof(T));
var mn = typeof(T).GetProperty(paramName);
var tc = typeof(T).GetProperty(condition);
if (mn == null || !ftrackData.Online)
return (T)k;
var data = GetTableData<T>();
if (!string.IsNullOrEmpty(paramName))
{
var retval = data.Select(t => mn.GetValue(t, null));
return (T)retval;
}
else
return (T)data.FirstOrDefault(t => mn.GetValue(t, null) > tc.GetType(t, null)).ToList();
}
I'd be looking to have the ">" in the final return change depending on an additional parameter passed into the arguments list. I know I can do a simple switch after the else, but is there some way to change the condition by insertion?

Your code doesn't really make any sense. The Select extension method takes a Func<T, TResult> which implies the return type should be IEnumerable<TResult> whereas you specify it as T.
In your question you want to do a Select and FirstOrDefault in the same method, but that is not possible since the result types will be different.
Select:
public static async Task<IEnumerable<TResult>> SelectData<T, TResult>(
string propertyName
)
{
if(string.IsNullOrWhiteSpace(propertyName))
{
return Enumerable.Empty<TResult>();
}
var dataTask = GetTableData<T>();
var tType = Expression.Parameter(typeof(T), "t");
var property = Expression.Property(tType, propertyName);
var selectExpression =
Expression.Lambda<Func<T, TResult>>(property, tType)
.Compile();
return (await dataTask).Select(selectExpression);
}
FirstOrDefault:
public static async Task<T> FirstOrDefaultData<T>(
string propertyName,
string conditionName,
Func<MemberExpression, MemberExpression, BinaryExpression> comparer
)
{
if(string.IsNullOrWhiteSpace(propertyName) ||
string.IsNullOrWhileSpace(conditionName) ||
comparer == null
{
return default(T);
}
var dataTask = GetTableData<T>();
var tType = Expression.Parameter(typeof(T), "t");
var property = Expression.Property(tType, propertyName);
var condition = Expression.Property(tType, conditionName);
var binaryExpression =
Expression.Lambda<Func<T, bool>>(comparer(property, condition), tType)
.Compile();
return (await dataTask).FirstOrDefault(binaryExpression);
}
Usage:
public class Foo
{
public string Bar { get; set; }
public bool Flag { get; set; }
}
var bars = SelectData<Foo, string>("Bar");
var foo = FirstOrDefaultData<Foo>("Bar",
"Flag",
(p, c) => Expression.GreaterThan(p, c));

Create an expression that will evaluate the result of a delegate and return the consequent or the alternate as the case may be

I want to retrieve the value of a property using a getter expression , but within that expression I want to evaluate a predicate and only return the value of the property if predicate evaluates to false, otherwise return a constant.
Something along the lines of (partially using code from here):
Expression<Func<U, bool>> exp = FuncToExpression(predicate);
var instance = Expression.Parameter(propertyInfo.DeclaringType, "instance");
var property = Expression.Property(instance, propertyInfo);
var convert = Expression.TypeAs(property, typeof(object));
var getLamba = Expression.Lambda(convert, instance);
var evaluate = Expression.Condition(exp, getLamba, Expression.Constant(alternate));
var lambda = Expression.Lambda(evaluate, instance);
return (Func<T, object>)lambda.Compile();
Any help here would be appreciated
Edit
More detail as per Jon's comment:
I am getting the following error on the evaluate variable :
{"Argument must be boolean"}
This is the FuncToExpression method :
private static Expression<Func<U, bool>> FuncToExpression<U>(Func<U, bool> predicate)
{
return argument => predicate(argument);
}
Edit 2
Complete Sample:
public class Test
{
public static void Main(string[] args)
{
TestPredicate test = new TestPredicate();
test.Number = 11;
Func<TestPredicate, object> callDelegate;
PropertyInfo info = typeof(TestPredicate).GetProperties().Where(a => a.Name == "Number").FirstOrDefault();
Func<int, bool> f = (x => x > 10 ? true : false);
if (info != null)
{
callDelegate = CreateValueGetDelegate<TestPredicate, int, int>(info, f, -1);
var item = (int) callDelegate(test);
Console.WriteLine(item); // expecting -1 here
}
Console.Read();
}
private static Func<T,object> CreateValueGetDelegate<T,U, S>(PropertyInfo propertyInfo, Func<U, bool> predicate, S alternate)
{
if (typeof(T) != propertyInfo.DeclaringType)
{
throw new ArgumentException();
}
Expression<Func<U, bool>> exp = FuncToExpression(predicate);
var instance = Expression.Parameter(propertyInfo.DeclaringType, "instance");
var property = Expression.Property(instance, propertyInfo);
var convert = Expression.TypeAs(property, typeof(object));
var getLamba = Expression.Lambda(convert, instance);
var evaluate = Expression.Condition(exp, getLamba, Expression.Constant(alternate));
var lambda = Expression.Lambda(evaluate, instance);
return (Func<T, object>)lambda.Compile();
}
private static Expression<Func<U, bool>> FuncToExpression<U>(Func<U, bool> predicate)
{
return argument => predicate(argument);
}
public class TestPredicate
{
public int Number { get; set; }
}
}

It would have helped if you'd said what currently going wrong, but I think you just need to get rid of the first Lambda call. I've made a few changes to the variable names too:
Expression<Func<U, bool>> test = FuncToExpression(predicate);
var parameter = Expression.Parameter(propertyInfo.DeclaringType, "instance");
var property = Expression.Property(parameter, propertyInfo);
var trueOption = Expression.TypeAs(property, typeof(object));
var falseOption = Expression.Constant(alternative);
var conditional = Expression.Condition(test, trueOption, falseOption);
var lambda = Expression.Lambda<Func<T, object>>(conditional, parameter);
return lambda.Compile();
If this doesn't work, please let us know in what way - ideally editing a short but complete sample program into your question.

This extension method will allow you to provide a selector (get the property), validator (validate the property) and a default value:
public static P GetValueOrDefault<T, P>(this T item, Func<T, P> selector, Func<P, bool> validator, P defaultValue)
{
if (item == null)
return defaultValue;
P value = selector(item);
if (validator == null || !validator(value))
return defaultValue;
return value;
}

Develop Reference

C# (C-Sharp) is a programming language developed by Microsoft that runs on the .NET Framework.

How to select column from string in efcore? - c#

Related

LINQ method, which Dynamically ordering data by column name I send

Linq orderbys from collection [duplicate]

Better way to Sort a List by any property

Using reflection to obtain values based on a specific query condition

Create an expression that will evaluate the result of a delegate and return the consequent or the alternate as the case may be

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