Topics

C#•8mo ago

✅ System.Data.SQLiteDatabase .NET 7.0 Reading Items From Database

public static List<GameModel> GetAllGames()
{
    using SQLiteConnection? conn = new(dbFile);
    using SQLiteCommand? cmd = conn.CreateCommand();
    SQLiteDataReader? reader;

    List<GameModel> games = new();

    conn.Open();

    reader = cmd.ExecuteReader();

    while (reader.Read())
    {
        GameModel game = new()
        {
            Id = Convert.ToInt32(reader["Id"].ToString()),
            Username = reader["User"].ToString(),
            Date = reader["Date"].ToString(),
            StartTime = reader["StartTime"].ToString(),
            EndTime = reader["EndTime"].ToString(),
            Duration = reader["Duration"].ToString(),
            Score = Convert.ToInt32(reader["Score"].ToString()),
            Total = Convert.ToInt32(reader["Total"].ToString()),
            Difficulty = reader["Difficulty"].ToString(),
            GameType = reader["GameType"].ToString()
        };

        games.Add(game);
    }

    return games;
}

public static List<GameModel> GetAllGames()
{
    using SQLiteConnection? conn = new(dbFile);
    using SQLiteCommand? cmd = conn.CreateCommand();
    SQLiteDataReader? reader;

    List<GameModel> games = new();

    conn.Open();

    reader = cmd.ExecuteReader();

    while (reader.Read())
    {
        GameModel game = new()
        {
            Id = Convert.ToInt32(reader["Id"].ToString()),
            Username = reader["User"].ToString(),
            Date = reader["Date"].ToString(),
            StartTime = reader["StartTime"].ToString(),
            EndTime = reader["EndTime"].ToString(),
            Duration = reader["Duration"].ToString(),
            Score = Convert.ToInt32(reader["Score"].ToString()),
            Total = Convert.ToInt32(reader["Total"].ToString()),
            Difficulty = reader["Difficulty"].ToString(),
            GameType = reader["GameType"].ToString()
        };

        games.Add(game);
    }

    return games;
}

I use this exact code (change a couple of variable names) in my other version of the math game I created and it keeps hollering at me object reference not set to an instance of an object when it comes to reader = cmd.ExecuteReader();. What is happening? There are 2 records in the database, but it just will not read.

No description

39 Replies

SG97•8mo ago

debug to determine what is null most likely cmd assuming dbFile is correct

Mekasu0124•8mo ago

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <connectionStrings>
        <add name="database" connectionString="Data Source=main.db" />
    </connectionStrings>
</configuration>

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <connectionStrings>
        <add name="database" connectionString="Data Source=main.db" />
    </connectionStrings>
</configuration>

this is my App.config file and at the top of my database file, I have the line

private static readonly string? dbFile = ConfigurationManager.ConnectionStrings["database"].ConnectionString;

private static readonly string? dbFile = ConfigurationManager.ConnectionStrings["database"].ConnectionString;

which I know is correct since it's saving the game records to the database, and creating the database if I delete it and re-run the program

SG97•8mo ago

debug on what's null no need to guess on a side note, dbFile is not a db file, it's a connection string. Naming is kinda confusing

Mekasu0124•8mo ago

it's the reader that's null

SG97•8mo ago

so in that case cmd.ExecuteReader() is returning null?

Mekasu0124•8mo ago

yes

SG97•8mo ago

what is the actual query you're running against the db what is the CommandText of the cmd

Mekasu0124•8mo ago

the code I have is in the initial post. I've never had to create CommandText when reading all items from the database.

I use this exact code (change a couple of variable names) in my other version of the math game I create...

It reads just fine and normal in my other math game version

SG97•8mo ago

I've no idea how you would read anything from a db without an actual query. Maybe someone else can help you, I'm out of suggestions

Mekasu0124•8mo ago

I'll try putting in a query for the CommandText and see what happens I appreciate your suggestions thus far

public static int GetNumber(string gameType, string difficulty)
{
    Random rng = new();
    int randomNumber = 0;

    if (gameType == "Addition" || gameType == "Subtraction")
    {
        if (difficulty == "Easy")
        {
            randomNumber = rng.Next(0, 300);
        }
        else if (difficulty == "Medium")
        {
            randomNumber = rng.Next(0, 600);
        }
        else if (difficulty == "Hard")
        {
            randomNumber = rng.Next(0, 900);
        }
    }
    else if (gameType == "Multiplication" || gameType == "Division")
    {
        if (difficulty == "Easy")
        {
            randomNumber = rng.Next(0, 100);
        }
        else if (difficulty == "Medium")
        {
            randomNumber = rng.Next(0, 200);
        }
        else if (difficulty == "Hard")
        {
            randomNumber = rng.Next(0, 300);
        }
    }

    return randomNumber;
}

public static int GetNumber(string gameType, string difficulty)
{
    Random rng = new();
    int randomNumber = 0;

    if (gameType == "Addition" || gameType == "Subtraction")
    {
        if (difficulty == "Easy")
        {
            randomNumber = rng.Next(0, 300);
        }
        else if (difficulty == "Medium")
        {
            randomNumber = rng.Next(0, 600);
        }
        else if (difficulty == "Hard")
        {
            randomNumber = rng.Next(0, 900);
        }
    }
    else if (gameType == "Multiplication" || gameType == "Division")
    {
        if (difficulty == "Easy")
        {
            randomNumber = rng.Next(0, 100);
        }
        else if (difficulty == "Medium")
        {
            randomNumber = rng.Next(0, 200);
        }
        else if (difficulty == "Hard")
        {
            randomNumber = rng.Next(0, 300);
        }
    }

    return randomNumber;
}

before I try that though, I do have a question for you. What is a better way to write this?

SG97•8mo ago

generally I don't do strings on predefined "types", I use enums

Mekasu0124•8mo ago

I tried doing

public static int GetNumber(...)
{
  Random rng = new();

  if (gameType == "Addition" || gameType == "Subtraction")
  {
      return difficulty switch
      {
          "Easy" => rng.Next(0,300),
          "Medium" => rng.Next(0,600),
          "Hard" => rng.Next(0,900)
      };
  }
  else if (gameType == "Multiplication" || gameType == "Division")
  {
      return difficulty switch
      {
          "Easy" => rng.Next(0,100),
          "Medium" => rng.Next(0,200),
          "Hard" => rng.Next(0,300)
      };
  }
}

public static int GetNumber(...)
{
  Random rng = new();

  if (gameType == "Addition" || gameType == "Subtraction")
  {
      return difficulty switch
      {
          "Easy" => rng.Next(0,300),
          "Medium" => rng.Next(0,600),
          "Hard" => rng.Next(0,900)
      };
  }
  else if (gameType == "Multiplication" || gameType == "Division")
  {
      return difficulty switch
      {
          "Easy" => rng.Next(0,100),
          "Medium" => rng.Next(0,200),
          "Hard" => rng.Next(0,300)
      };
  }
}

but it told me that not all code paths returned a value... wdym?

SG97•8mo ago

I don't like matching strings anywhere, especially when you know what gametypes and difficulties you have

Mekasu0124•8mo ago

so what do you do instead?

SG97•8mo ago

        public enum GameType
        {
            Addition,
            Substraction
        }

        public enum Difficulty
        {
            Easy,
            Medium,
            Hard
        }

        public enum GameType
        {
            Addition,
            Substraction
        }

        public enum Difficulty
        {
            Easy,
            Medium,
            Hard
        }

Mekasu0124•8mo ago

public Enum GameTypes
{
  Addition,
  Subtraction,
  Multiplication,
  Division
}

public Enum Difficulties
{
  Easy,
  Medium,
  Hard
}

public Enum GameTypes
{
  Addition,
  Subtraction,
  Multiplication,
  Division
}

public Enum Difficulties
{
  Easy,
  Medium,
  Hard
}

so let's say I did this in my Helpers.cs file, how would I go about using that for what I'm wanting to do?

SG97•8mo ago

I think you need a discard for your switch expression oh

Mekasu0124•8mo ago

the discard plus changing if else if to an else fixed that problem are Enums more efficient?

SG97•8mo ago

you're not handling the case where gametype is not addition/substraction/multiplication/division ah, you changed to else all good

Mekasu0124•8mo ago

I switched it from an if/else if to an if/else and that fixed that so let's say theoretically I created the two enums shown here. How would I use them in place of my strings and such?

SG97•8mo ago

instead of passing in "Addition" as the gameType you pass in GameType.Addition same goes for the difficulty

Mekasu0124•8mo ago

oh ok. I'm trying to set one up to learn how to use them, but I'm not sure what I'm doing wrong

No description

Mekasu0124•8mo ago

do they getters/setters?

SG97•8mo ago

no

Mekasu0124•8mo ago

ok

SG97•8mo ago

are you using top level statements

Mekasu0124•8mo ago

so it's enum not Enum

SG97•8mo ago

ah yes

Mekasu0124•8mo ago

I don't know what a top level statement is and I've never used enums like this before so I think I'll keep the strings if it's not going to hurt anything

SG97•8mo ago

the idea is that the developer cannot pass in gameType as "asdf" and difficulty "fdas" as they are predefined as enums and generally matching magic strings is a code smell but yes, one problem at a time

Mekasu0124•8mo ago

public static void ShowMenu(string username, string date)
{
    string choice = GetMenuChoice();

    switch (choice)
    {
        case "Addition":
        case "Subtraction":
        case "Multiplication":
        case "Division":
        case "Random":
            string difficulty = GetGameDifficulty();
            int maxQuestions = GetNumberOfQuestions();

            Game.StartGame(username, date, choice, difficulty, maxQuestions);
            break;

        case "Previous Games":
            Game.ShowPreviousGames(username, date);
            break;

        case "Quit Game":
            ColorCon.WriteLine("Exiting Application", ConsoleColor.Red);
            Environment.Exit(0);
            break;
    }
}

public static string GetMenuChoice()
{
    Console.Clear();
    string menuOptions = """
                            What Would You Like To Do?

                            A - Addition
                            S - Subtraction
                            M - Multiplication
                            D - Division
                            R - Random
                            P - Previous Games
                            Q - Quit Game
                             
                             
                            Your Selection: 
                            """;
    List<string> choices = new() { "a", "s", "m", "d", "r", "p", "q" };
    string errorText = "Invalid Input. Choice Must Be: \"A\", \"S\", \"M\", \"D\", \"R\", \"P\", or \"Q\"";

    string choice = ColorCon.GetStringFromConsole(
        prompt: menuOptions,
        color: ConsoleColor.Cyan,
        validator: x => choices.Contains(x.ToLower()),
        errorMessage: errorText);

    return choice switch
    {
        "a" or "A" => "Addition",
        "s" or "S" => "Subtraction",
        "m" or "M" => "Multiplication",
        "d" or "D" => "Division",
        "r" or "R" => "Random",
        "p" or "P" => "Previous Games",

public static void ShowMenu(string username, string date)
{
    string choice = GetMenuChoice();

    switch (choice)
    {
        case "Addition":
        case "Subtraction":
        case "Multiplication":
        case "Division":
        case "Random":
            string difficulty = GetGameDifficulty();
            int maxQuestions = GetNumberOfQuestions();

            Game.StartGame(username, date, choice, difficulty, maxQuestions);
            break;

        case "Previous Games":
            Game.ShowPreviousGames(username, date);
            break;

        case "Quit Game":
            ColorCon.WriteLine("Exiting Application", ConsoleColor.Red);
            Environment.Exit(0);
            break;
    }
}

public static string GetMenuChoice()
{
    Console.Clear();
    string menuOptions = """
                            What Would You Like To Do?

                            A - Addition
                            S - Subtraction
                            M - Multiplication
                            D - Division
                            R - Random
                            P - Previous Games
                            Q - Quit Game
                             
                             
                            Your Selection: 
                            """;
    List<string> choices = new() { "a", "s", "m", "d", "r", "p", "q" };
    string errorText = "Invalid Input. Choice Must Be: \"A\", \"S\", \"M\", \"D\", \"R\", \"P\", or \"Q\"";

    string choice = ColorCon.GetStringFromConsole(
        prompt: menuOptions,
        color: ConsoleColor.Cyan,
        validator: x => choices.Contains(x.ToLower()),
        errorMessage: errorText);

    return choice switch
    {
        "a" or "A" => "Addition",
        "s" or "S" => "Subtraction",
        "m" or "M" => "Multiplication",
        "d" or "D" => "Division",
        "r" or "R" => "Random",
        "p" or "P" => "Previous Games",

        "q" or "Q" => "Quit Game",
        _ => throw new Exception("Error Determining Game Type In Helper Function")
    };
}

public static string GetGameDifficulty()
{
    string difficultyOptions = """

                                Select A Difficulty

                                E - Easy
                                M - Medium
                                H - Hard

                                Your Selection: 
                                """;

    List<string> choices = new() { "e", "m", "h" };
    string errorText = "Invalid Input. Choice Must Be: \"E\", \"M\", or \"H\"";

    string difficulty = ColorCon.GetStringFromConsole(
        prompt: difficultyOptions,
        color: ConsoleColor.Magenta,
        validator: x => choices.Contains(x.ToLower()),
        errorMessage: errorText);

    return difficulty switch
    {
        "e" => "Easy",
        "m" => "Medium",
        "h" => "Hard"
    };
}

        "q" or "Q" => "Quit Game",
        _ => throw new Exception("Error Determining Game Type In Helper Function")
    };
}

public static string GetGameDifficulty()
{
    string difficultyOptions = """

                                Select A Difficulty

                                E - Easy
                                M - Medium
                                H - Hard

                                Your Selection: 
                                """;

    List<string> choices = new() { "e", "m", "h" };
    string errorText = "Invalid Input. Choice Must Be: \"E\", \"M\", or \"H\"";

    string difficulty = ColorCon.GetStringFromConsole(
        prompt: difficultyOptions,
        color: ConsoleColor.Magenta,
        validator: x => choices.Contains(x.ToLower()),
        errorMessage: errorText);

    return difficulty switch
    {
        "e" => "Easy",
        "m" => "Medium",
        "h" => "Hard"
    };
}

well if I use those enums, then these functions will have to update accordingly and I don't know how to do that

SG97•8mo ago

you can always improve the codebase later ofc you do

Mekasu0124•8mo ago

so what. List<string> choices = new() { "e", "m", "h" }; would become....what....List<enum> choices = new() { Difficulties.Easy, Difficulties.Medium, Difficulties.Hard };?

SG97•8mo ago

no, those are user inputs you map them to gametype/difficulty later on

Mekasu0124•8mo ago

so then should it be

public enum GameTypes
{
  Addition = "Addition",
  ...
}

public enum GameTypes
{
  Addition = "Addition",
  ...
}

? yea I'm lost. I'm just not going to worry about it. Thanks anyways though

SG97•8mo ago

always make it work first, then improve

Mekasu0124•8mo ago

the game is done. It's complete. Everything works now and works as it should. I'm pushing a release to my github as we speak. I just wanted to learn about the enums and how to use them is all

SG97•8mo ago

you figured out the db problem?

Mekasu0124•8mo ago

yep. I thought for some odd ball reason that I didn't need to set a cmd.CommandText = "SELECT * FROM [table]"; and that turned out to be my problem

We are a programming server aimed at coders discussing everything related to C# (CSharp) and .NET.

52KMembers

View on Discord

Want results from more Discord servers?

Add your server

More Posts

✅ Switch Case Not Executing Properly```cs public static void ShowMenu(string username, string date) { string choice = GetMenuChoice(❔ How to install a xamarinios10 package onto net7.0-ios16.4The error I got is ``` error NU1202: Package StormUp.Xamarin.IQKeyboardManager 6.5.4.2 is not compa ❔ visual studio keyboard shortcutsas in visual studio, when pressing alt to remove the switch to the top panel, I constantly switch to ✅ launchSettings.json being ignored completelyAll of a sudden, my .NET Visual Studio project has stopped respecting my `launchSettings.json` file.✅ Unit Testing HttpClientHello, I'm currently trying to write some unit tests for a class that uses an HttpClientFactory thro are my getters and setters correct?Before I work on the rest of my code, please let me know if there are any errors in my getters and s ❔ Opinions wanted on a new server for information services workersWe are launching a new Discord server aimed at fostering collaboration, knowledge sharing, and servi MVVN w/ Dependency Injection: Best Practice*This question is for those who have personal experience building applications with the use of an MV Issue with AddUserStore in asp.net coreHi. I have an issue with the following line of code in asp.net core ```c builder.Services.AddIdentit ❔ EFCore Change Tracker ConfusionAssuming a entity `Order` with a relationship to entity `Table` ```csharp var order = new Order() {