Linq expression filter in IQueryable

Question

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"?

Answer 1

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));