CODEWITHSUNDEEP
c#linq
D J
D J

Reputation: 7028

How to get list for a property of a class from its collection

I have scenario where I need to get the collection of values of a property of class.

public class Person
{
    public string Name { get; set; }
    public string Property1 { get; set; }
    public string Property2 { get; set; }
}

public class PersonCollection : List<Person>
{
    public object[] GetValues(string propertyName)
    {
        // best way to implement this method?
        return null;
    }
}

I want to avoid the much iterations. Any idea will help.

Upvotes: 3

Views: 1384

Answers (7)

Ken Kin
Ken Kin

Reputation: 4683

A simple idea without using reflection would be like this: 

public partial class PersonCollection: List<Person> {
    public object[] GetValues(String propertyName) {
        return (
            from it in this
            let x=
                "Name"==propertyName
                    ?it.Name
                    :"Property1"==propertyName
                        ?it.Property1
                        :"Property2"==propertyName
                            ?it.Property2
                            :default(object)
            where null!=x
            select x).ToArray();
    }
}

But I'd rather return an IEnumerable for not to enumerate eagerly: 

public partial class PersonCollection: List<Person> {
    public IEnumerable GetValues(String propertyName) {
        return
            from it in this
            let x=
                "Name"==propertyName
                    ?it.Name
                    :"Property1"==propertyName
                        ?it.Property1
                        :"Property2"==propertyName
                            ?it.Property2
                            :default(object)
            where null!=x
            select x;
    }
}

Upvotes: 2

Erik Schierboom
Erik Schierboom

Reputation: 16636

A simple solution would be one that uses LINQ's Select method:

using System;
using System.Collections.Generic;
using System.Linq;

public class Person
{
    public string Name { get; set; }
    public string Property1 { get; set; }
    public string Property2 { get; set; }
}

public class PersonCollection : List<Person>
{
    public object[] GetValues(string propertyName)
    {
        if (propertyName == "Name")
        {
            return this.Select(p => p.Name).ToArray();
        }
        else if (propertyName == "Property1")
        {
            return this.Select(p => p.Property1).ToArray();
        }
        else if (propertyName == "Property2")
        {
            return this.Select(p => p.Property1).ToArray();
        }

        // best way to implement this method?
        return null;
    }
}

You can also use expression trees to allow for a type-safe accessor lambda to be used as an argument:

public object[] GetValues(Expression<Func<Person, object>> propertyNameExpression)
{
    var compiledPropertyNameExpression = propertyNameExpression.Compile();

    if (propertyNameExpression.Body.NodeType == ExpressionType.MemberAccess)
    {
        return this.Select(compiledPropertyNameExpression).ToArray();
    }

    throw new InvalidOperationException("Invalid lambda specified. The lambda should select a property.");
}

You can then use this as follows:

var personNames = personCollection.GetValues(p => p.Name)

Upvotes: 2

Ramunas
Ramunas

Reputation: 3883

A bit of Linq magic:

public object[] GetValues(Expression<Func<Person, object>> exp)
{
    var function = exp.Compile();
    return this.Select(function).ToArray();
}

Usage:

// assuming coll in a PersonCollection
var names = coll.GetValues(p => p.Name);

Upvotes: 4

shamp00
shamp00

Reputation: 11326

Here's a working program

public class Person
{
    public string Name { get; set; }
    public string Property1 { get; set; }
    public string Property2 { get; set; }
}

public class PersonCollection : List<Person>
{
    public object[] GetValues(string propertyName)
    {
        var result = new List<object>();
        foreach (Person item in this)
        {
            result.Add(item.GetType().GetProperty(propertyName).GetValue(item));
        }
        return result.ToArray();
    }
}
class Program
{
    static void Main(string[] args)
    {
        var collection = new PersonCollection();
        collection.Add(new Person(){Name = "George", Property1 = "aaa", Property2 = "bbbb"});
        collection.Add(new Person(){Name = "Peter", Property1 = "ccc", Property2 = "dddd"});
        var objects = collection.GetValues("Property1");
        foreach (object item in objects)
        {
            Console.WriteLine(item.ToString());
        }
        Console.Read();
    }
}

Upvotes: 1

petchirajan
petchirajan

Reputation: 4352

try this,

public object[] GetValues(string propertyName)
{
    List<object> result = new List<object>();
    PropertyInfo propertyInfo = typeof(Person).GetProperty(propertyName);
    this.ForEach(person => result.Add(propertyInfo.GetValue(person)));
    return result.ToArray();
}

Upvotes: 1

Taj
Taj

Reputation: 1728

use Reflection

Person P = new Person(); object obj = p.GetType().GetProperty(propertyName).GetValue(p, null);

Upvotes: 1

Keren Caelen
Keren Caelen

Reputation: 1466

If you are working with entity framework, you can use this.GetAll();

Upvotes: 0

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