Linq query to find objects in nested objects

Question

Complete code is attached below. I want to find all Cars objects that has a certain color.

The Vehicles list consists of two lists of type Cars. The Cars lists consist of objects of type Colours.

Instead of using foreach iterations, what would a Linq query look like?

using System.Collections.Generic;

public class Test
{
    public void testitall()
    {
        List<Cars> test = FindCarByColour("Red");
    }

    /// <summary>
    /// Find all cars with property ColourName like colourcriteria
    /// </summary>
    /// <param name="colourcriteria"></param>
    /// <returns></returns>
    private List<Cars> FindCarByColour(string colourcriteria)
    {
     // Populate data classes
        Colours Col1 = new Colours();
        Col1.ColourName ="Red";
        Colours Col2 = new Colours();
        Col2.ColourName ="Blue";
        List<Cars> CarList1 = new List<Cars>();
        CarList1.Add(new Cars { Name = "Saab", ColourProperties = Col1 });
        CarList1.Add(new Cars { Name = "Citroen", ColourProperties = Col2});
        List<Cars> CarList2 = new List<Cars>();
        CarList2.Add(new Cars { Name = "Daf", ColourProperties = Col1 });
        CarList2.Add(new Cars { Name = "Vauxhall", ColourProperties = Col2 });
        List<Vehicles> vehicleList = new List<Vehicles>();
        vehicleList.Add(new Vehicles { Vechicle = "SmallCar", Cars = CarList1 });
        vehicleList.Add(new Vehicles { Vechicle = "MediumCar", Cars = CarList2 });

        // Search 
        List<Cars> ListOfFindings = new List<Cars>();
        foreach (Vehicles vehicleItem in vehicleList)
        {
            foreach (Cars caritem in vehicleItem.Cars)
            {
                if (caritem.Name != null && caritem.ColourProperties.ColourName == colourcriteria)
                {
                    ListOfFindings.Add(caritem);
                }
            }
        }
        return ListOfFindings;
    }

    // Data classes
    public class Vehicles
    {
        public string Vechicle { get; set; }
        public List<Cars> Cars { get; set; }
    }
    public class Cars
    {
        public string Name { get; set; }
        public Colours ColourProperties { get; set; }
    }
    public class Colours
    {
        public string ColourName { get; set; }
    }

}

Try this : List<Cars> ListOfFindings = vehicleList.SelectMany(x => (List<Cars>)x.Cars).Where(y => y.ColourProperties.ColourName == colourcriteria).ToList(); — jdweng
– jdweng, Commented Nov 12, 2015 at 1:22

a little sheep · Accepted Answer · 2015-11-12 01:03:56Z

2

You could probably use something like:

var listOfFindings = (from vehicleItem in vehicleList
                      from carItem in vehicleItem.Cars
                      where carItem.Name != null
                      && carItem.ColourProperties.ColourName == colourcriteria
                      select carItem).ToList();

or

var listOfFindings = vehicleList.SelectMany(vehicleItem => vehicleItem.Cars).Where(carItem => carItem.Name != null && carItem.ColourProperties.ColourName == colourcriteria).ToList();

Depending on what style of Linq you want to use.

answered Nov 12, 2015 at 1:03

a little sheep

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3 Comments

netfed Over a year ago

Thank you ever so much. Thanks also for the alternative.

netfed Over a year ago

I see there is a very important difference in the use of Select vs. SelectMany. The Select keyword should really be named SelectOne, or is it more to it?

a little sheep Over a year ago

You could say that, yeah. Both methods are used to shape/project the structure of the results. Select keeps the sequence as-is and only changes the shape of the data (so it returns one element per element from the source sequence), while SelectMany is used to flatten multiple sequences into one sequence (so every element in each of the vehicle's 'cars' sequences are returned in one big sequence of car elements, if that makes sense!).

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