Styjun

I want to create generic expression filtering in IQueryable

public class Vehicle
 
 public int Id get; set; 
 public string VehicleNO get; set; 
 public int DriverId get; set; 
 public Driver Driver get;set;
 

 public class Driver
 
 public int Id get; set; 
 public string Name get; set; 
 

operator = "Contain", field name = "Driver.Name", Value filter =
"Micheal"

I don't know how to filter driver name.
Here is my full code

IQueryable<SysClientSiteUser> query = entity.SysClientSiteUsers.Include(i => i.SysClientSiteRole);

Dictionary<string, string> dtFilter = new Dictionary<string, string>();
dtFilter.Add("VehicleNo", "A123");


Dictionary<Type, Func<string, object>> lookup = new Dictionary<Type, Func<string, object>>();


lookup.Add(typeof(string), x => return x; );
lookup.Add(typeof(long), x => return long.Parse(x); );
lookup.Add(typeof(int), x => return int.Parse(x); );
lookup.Add(typeof(double), x => return double.Parse(x); );

var paramExpr = Expression.Parameter(typeof(Vehicle), "VehicleNo");

var keyPropExpr = Expression.Property(paramExpr, "VehicleNo");

if (!lookup.ContainsKey(keyPropExpr.Type))
 throw new Exception("Unknown type : " + keyPropExpr.Type.ToString());

var typeDelegate = lookup[keyPropExpr.Type];
var constantExp = typeDelegate("A123");
var eqExpr = Expression.Equal(keyPropExpr, Expression.Constant(constantExp));
var condExpr = Expression.Lambda<Func<SysClientSiteUser, bool>>(eqExpr, paramExpr);
query = query.Where(condExpr);

for normal field, it's working. But if I want to call Driver name. it's not work. How to call "Driver.Name"?

You can use a helper function to convert a nested property name string to an Expression that accesses that property for a given ParameterExpression and type:

private static Expression MakePropertyExpression<T>(string propertyName, Expression baseExpr) =>
 propertyName.Split('.').Aggregate(baseExpr, (b, pname) => Expression.Property(b, pname));