Myujth

I want to create a dynamic filter for my repositories using linq expressions, I have other filters but i don't know how to make the next one using expressions: (the condition was taked from here)

var result = _studentRepotory.GetAll().Where(s => 
SqlFunctions.StringConvert((double)s.Id).Contains("91")).ToList();

I have a method that receives the value of a property, the propertyName and the filter operator type (enum):

public static class Helper 
 public static Expression<Func<T, bool>> GetExpression<T>(object value, string propertyName, FilterOperatorType FilterType)
 
 var parameter = Expression.Parameter(typeof(T));
 var property = ExpressionUtils.GetPropertyChild(parameter, propertyName);
 var constValue = Expression.Constant(value);

 BinaryExpression expresion = null;
 switch (FilterType)
 
 case FilterOperatorType.Equal:
 expresion = Expression.Equal(property, constValue);
 break;
 case FilterOperatorType.Greater:
 expresion = Expression.GreaterThan(property, constValue);
 break;
 case FilterOperatorType.Less:
 expresion = Expression.LessThan(property, constValue);
 break;
 case FilterOperatorType.GreaterOrEqual:
 expresion = Expression.GreaterThanOrEqual(property, constValue);
 break;
 case FilterOperatorType.LessOrEqual:
 expresion = Expression.LessThanOrEqual(property, constValue);
 break;
 

 var lambda = Expression.Lambda<Func<T, bool>>(expresion, parameter);
 return lambda;
 

So, I want to add a new opertator type Contains that will evaluate if an integer contains some digits, in the first block of code I do it, but I want to do it with linq expressions using generics.

At the end I wil have:

Expression<Func<Student, bool>> where = Helper.GetExpression<Student>("91", "Id", FilterOperatorType.Contains);
var result = _studentRepotory.GetAll().Where(where).ToList();

The query should return all the students when the Id contains the digits 91.

Please help me, and tell me if you understand.

I'm at 2:00 am and still working on this, the brain works better at that time hehehe, here is the solution for create the expression:

object value = "91";

var parameter = Expression.Parameter(typeof(Student));
var property = ExpressionUtils.GetPropertyChild(parameter, "Id");
var constValue = Expression.Constant(value);

var expressionConvert = Expression.Convert(property, typeof(double?));

var methodStringConvert = typeof(SqlFunctions).GetMethod("StringConvert",
 BindingFlags.Public | BindingFlags.Static, null,
 CallingConventions.Any,
 new Type typeof(double?) ,
 null);

var methodContains = typeof(string).GetMethod("Contains", 
 BindingFlags.Public | BindingFlags.Instance,
 null, CallingConventions.Any,
 new Type typeof(String) , null);

var expresionStringConvert = Expression.Call(methodStringConvert, expressionConvert);
var expresionContains = Expression.Call(expresionStringConvert, methodContains, constValue);
var lambdaContains = Expression.Lambda<Func<Student, bool>>(expresionContains, parameter);

Now you can use lambdaContains in the Where method of the studentRepository