Get Data From Deserialized List By Type - C# Discussion Boards

22-Jan-20 8:45

I have a serialized collection of objects, such as

GroupEntity
  - ConfigEntity
     - DefinitionEntity
  - ConfigEntity
     - DefinitionEntity
  - ConfigEntity
     - DefinitionEntity

GroupEntity
  - ConfigEntity
     - DefinitionEntity
  - ConfigEntity
     - DefinitionEntity
  - ConfigEntity
     - DefinitionEntity

Given a generic type parameter T, how would you extract all items from the list for that type? So, if I have a class

public class Parser<T>
{
    public T Data { get; set; }
    public void LoadDataFromFile(string fileName)
    {
        // Deserialize the entire file into the master list ;
        List<GroupEntity> allData = Serialization.DeSerializeObject<List<GroupEntity>>(fileName);     

        // Get the type of the class's Parameter
        Type parameterType = typeof(T);

        // Now get all the objects of type T from the list
        //Data =  ????
    }
}

and I instantiated it as

var parser = new Parser<ConfigEntity>();  // Load only Configurations
parser.LoadDataFromFile(fileName);

var parser = new Parser<DefinitionsEntity>();  // Load only Definitions
parser.LoadDataFromFile(fileName);

This should then extract ONLY the type of entities into the Data property defined by the generic parameter.

I could write some looping code, but I would then need conditional code for each type. Is this possible with Linq?

If it's not broken, fix it until it is.
Everything makes sense in someone's mind.
Ya can't fix stupid.

Richard Deeming22-Jan-20 9:01

22-Jan-20 9:01

That depends.

Do you have a list of objects of different types, where ConfigEntity and DefinitionEntity both inherit from GroupEntity?

class GroupEntity { }
class ConfigEntity : GroupEntity { }
class DefinitionEntity : GroupEntity { }

Or do you have a serialized object graph, where a GroupEntity contains one or more ConfigEntity objects, each of which contains one or more DefinitionEntity objects?

class GroupEntity
{
    public List<ConfigEntity> ConfigEntities { get; }
}

class ConfigEntity
{
    public List<DefinitionEntity> DefinitionEntities { get; }
}

class DefinitionEntity { }

If it's the former, then OfType will do the trick:

public class Parser<T> where T : GroupEntity
{
    public List<T> Data { get; set; }
    
    public void LoadDataFromFile(string fileName)
    {
        List<GroupEntity> allData = Serialization.DeSerializeObject<List<GroupEntity>>(fileName); 
        Data = allData.OfType<T>().ToList();
    }
}

If it's the latter, then you're going to need conditional code for each type.

"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer

Kevin Marois22-Jan-20 9:15

22-Jan-20 9:15

1) They all individually inherit from EntityBase

2) I have a serialized object graph

If it's not broken, fix it until it is.
Everything makes sense in someone's mind.
Ya can't fix stupid.

Kevin Marois22-Jan-20 11:12

22-Jan-20 11:12

The problem I see is that there's no way to make the Data property generic.

I can get all of the types like this:

private void LoadDataFromFile(string fileName)
{
    try
    {
        // Lists
        List<RuleGroupEntity> groups = new List<RuleGroupEntity>();
        List<RuleConfigurationEntity> configs = new List<RuleConfigurationEntity>();
        List<RuleDefinitionEntity> definitions = new List<RuleDefinitionEntity>();

        // Deserialize into the Groups
        groups = Serialization.DeSerializeObject<List<RuleGroupEntity>>(fileName);

        // Go through all the data and load the lists
        foreach (var group in groups)
        {
            configs.AddRange(group.RuleConfigurations);

            foreach (var config in group.RuleConfigurations)
            {
                definitions.Add(config.RuleDefinition);
            }
        }

        // Get the parameter type
        Type parameterType = typeof(T);

        // If T is Configurations, the load the Data T property with the configs list
        if (parameterType == typeof(RuleConfigurationEntity))
        {
            Data = (T)Activator.CreateInstance(typeof(T), configs); // <== Something like this is what I want.
        }
    }
    catch (Exception e)
    {
    }
}

But I then need to assign one of those lists to Data T. Not sure how to convert that.

If it's not broken, fix it until it is.
Everything makes sense in someone's mind.
Ya can't fix stupid.

Richard Deeming23-Jan-20 0:48

23-Jan-20 0:48

Something like this should work:

public class Parser<T> where T : EntityBase
{
    public List<T> Data { get; set; }
    
    public void LoadDataFromFile(string fileName)
    {
        List<RuleGroupEntity> groups = Serialization.DeSerializeObject<List<RuleGroupEntity>>(fileName);
        switch (typeof(T))
        {
            case typeof(RuleGroupEntity):
            {
                Data = (List<T>)(object)groups;
                break;
            }
            case typeof(RuleConfigurationEntity):
            {
                List<RuleConfigurationEntity> configs = groups.SelectMany(g => g.RuleConfigurations).ToList();
                Data = (List<T>)(object)configs;
                break;
            }
            case typeof(RuleDefinitionEntity):
            {
                List<RuleDefinitionEntity> definitions = groups.SelectMany(g => g.RuleConfigurations).Select(c => c.RuleDefinition).ToList();
                Data = (List<T>)(object)definitions;
                break;
            }
            default:
            {
                throw new NotSupportedException($"Type '{typeof(T)}' is not supported.");
            }
        }
    }
}

However, I'm never entirely convinced by a generic type which switches on the type parameter. Perhaps you could use specific parser types instead?

public abstract class Parser<T> where T : EntityBase
{
    public List<T> Data { get; set; }
    
    public void LoadDataFromFile(string fileName)
    {
        List<RuleGroupEntity> groups = Serialization.DeSerializeObject<List<RuleGroupEntity>>(fileName);
        LoadDataFromGroups(groups);
    }
    
    protected abstract void LoadDataFromGroups(List<RuleGroupEntity> groups);
}

public class RuleGroupEntityParser : Parser<RuleGroupEntity>
{
    protected override void LoadDataFromGroups(List<RuleGroupEntity> groups)
    {
        Data = groups;
    }
}

public class RuleConfigurationEntityParser : Parser<RuleConfigurationEntity>
{
    protected override void LoadDataFromGroups(List<RuleGroupEntity> groups)
    {
        Data = groups.SelectMany(g => g.RuleConfigurations).ToList();
    }
}

public class RuleDefinitionEntityParser : Parser<RuleDefinitionEntity>
{
    protected override void LoadDataFromGroups(List<RuleGroupEntity> groups)
    {
        Data = groups.SelectMany(g => g.RuleConfigurations).Select(c => c.RuleDefinition).ToList();
    }
}

"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer

Kevin Marois23-Jan-20 7:35

23-Jan-20 7:35

OK, so I implemented your first code snippet. It works.

What I left out before was that this all goes in a repository. I currently have a MongoDB repo, and now I'm implementing the IRepository interface to deal with the serialized version of the data. Now I have a new issue:

This Works

public T Get(Guid id)
{
    return Data.Where(x => x.Id == id).FirstOrDefault();
}

This Doesn't Compile

public T Get(Expression<Func<T, bool>> predicate)
{
    return Data.Where(predicate).FirstOrDefault();
}

The error is "'List<t>' does not contain a definition for 'Where' and the best extension method overload 'Queryable.Where<t>(IQueryable<t>, Expression<func<t, bool="">>)' requires a receiver of type 'IQueryable<t>'"

The problem is that List<t> isn't an IQueryable. If I change method signaature to accept a delegate instead of an expression, it works.

public T Get(Func<T, bool> predicate)
{
    return Data.Where(predicate).FirstOrDefault();
}

I could add this method to the interface, but I'd rather not change existing code if I don't have to. And it causes abiguity beetween the two Get methods.

I'd like to hear your thoughts on this. And thanks for your help so far.

If it's not broken, fix it until it is.
Everything makes sense in someone's mind.
Ya can't fix stupid.

Richard Deeming23-Jan-20 9:34

Queryable.AsQueryable Method (System.Linq) | Microsoft Docs[^]

23-Jan-20 9:34

How about:

public T Get(Expression<Func<T, bool>> predicate)
{
    return Data.AsQueryable().Where(predicate).FirstOrDefault();
}

"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer

Kevin Marois23-Jan-20 7:51

23-Jan-20 7:51

This seems to work

Interface Change

// Old
//T Get(Expression<Func<T, bool>> predicate);

// new
T Get(Func<T, bool> predicate);

Mongo Repo

//public T Get(Expression<Func<T, bool>> predicate)
//{
//    var collection = GetCollection();
//    return collection.AsQueryable().Where(predicate).FirstOrDefault();
//}

public T Get(Func<T, bool> predicate)
{
    var collection = GetCollection().AsQueryable();
    return collection.Where(predicate).FirstOrDefault();
}

XML Repo

//public T Get(Expression<Func<T, bool>> predicate)
//{
//    throw new NotImplementedException();
//}

public T Get(Func<T, bool> predicate)
{
    return Data.AsQueryable().Where(predicate).FirstOrDefault();
}

If it's not broken, fix it until it is.
Everything makes sense in someone's mind.
Ya can't fix stupid.

BillWoodruff22-Jan-20 21:44

BillWoodruff

22-Jan-20 21:44

example of generic return filter ... you write the Linq version Smile | :)

... usage example in some method:

required: using GRFExample;    

    var gevalues = Example.GetByType<GroupEntity>(Example.Test1().ToArray()).Cast<GroupEntity>();
            
    var cevalues = Example.GetByType<ConfigEntity>(Example.Test1().ToArray()).Cast<ConfigEntity>();
    
    var devalues = Example.GetByType<DefinitionEntity>(Example.Test1().ToArray()).Cast<DefinitionEntity>();

using System.Collections.Generic;

namespace GRFExample
{
    public static class Example
    {
        private static int id = 0;

        public static IEnumerable<GroupEntity> Test1()
        {
            for (var i = 0; i < 5; i++)
            {
                var ge = new GroupEntity();

                for (var j = 0; j < 4; j++)
                {
                    var ce = new ConfigEntity();
                    ce.dee = new DefinitionEntity(id++);
                    ge.cees.Add(ce);
                }

                yield return ge;
            }
        }

        public static IEnumerable<TheBase> GetByType<T>(params GroupEntity[] bees)
        {
            var pType = typeof(T).Name;

            foreach (var b in bees)
            {
                switch (pType)
                {
                    case "B":
                        yield return b;
                        break;

                    case "C":
                        foreach (var c in b.cees) yield return c;
                        break;

                    case "D":
                        foreach (var c in b.cees) yield return c.dee;
                        break;
                }
            }
        }
    }

    public class TheBase
    {
    }

    public class GroupEntity : TheBase
    {
        public List<ConfigEntity> cees = new List<ConfigEntity>();
    }

    public class ConfigEntity : TheBase
    {
        public DefinitionEntity dee;
    }

    public class DefinitionEntity : TheBase
    {
        public int id;

        public DefinitionEntity(int id)
        {
            this.id = id;
        }
    }
}

«One day it will have to be officially admitted that what we have christened reality is an even greater illusion than the world of dreams.» Salvador Dali

Exception thrown: 'System.IO.FileNotFoundException' sqlite

Gerry Schmitz23-Jan-20 4:14

Gerry Schmitz

23-Jan-20 4:14

Use interfaces; "generics" aren't that generic in this case.

It was only in wine that he laid down no limit for himself, but he did not allow himself to be confused by it.
― Confucian Analects: Rules of Confucius about his food

Member 1472399222-Jan-20 8:41

Member 14723992

22-Jan-20 8:41

So I'm working on a plugin for an application. So I'm creating a ClassLibrary in C#. I'm stuck at this point where it throws that error telling me that System.data.sqlite.dll isn't found. But I've checked it and even manually replaced the file, and it's there.

Another thing to note is that since it's a ClassLibrary, there no executable, it runs when the button on the application is pressed to run the plugin. Also this is my first time working with sqlite in C#. So I followed someone's instructions, which told me to simply get sqlite core from nuget and get dapper from nuget. I've done that. Do I need to get something from system.data.sqlite's website?

Please excuse the way I've asked too many question, but I'm just puzzled. This is my first time working with a Class Library and I never thought it'd be so much different to a console or winform application.

Regards

Re: Exception thrown: 'System.IO.FileNotFoundException' sqlite

Richard Deeming22-Jan-20 8:54