NET Maui – How do I run a SQLight query with parms and populate a List of objects?

Introduction

Are you tired of struggling with running SQLite queries with parameters in .NET Maui? Do you find yourself wondering how to populate a list of objects with the results of your query? Well, wonder no more! In this comprehensive guide, we’ll take you by the hand and walk you through the process of running a SQLite query with parameters and populating a list of objects in .NET Maui.

Setting up SQLite in .NET Maui

Before we dive into running queries, we need to set up SQLite in our .NET Maui project. First, add the `SQLite.NET` NuGet package to your project. You can do this by right-clicking on your project in Visual Studio, selecting “Manage NuGet Packages”, and searching for `SQLite.NET`.

Once the package is installed, create a new class to handle your database operations. Let’s call it `DatabaseService`.

public class DatabaseService
{
    private readonly SQLiteConnection _connection;

    public DatabaseService(string databasePath)
    {
        _connection = new SQLiteConnection(databasePath);
        _connection.CreateTable<MyTable>();
    }
}

In this example, we’re creating a `DatabaseService` class that takes a database path in its constructor. We’re then creating a new `SQLiteConnection` instance and creating a table called `MyTable`.

Running a SQLite Query with Parameters

Now that we have our database set up, let’s create a method to run a SQLite query with parameters. We’ll create a new method called `GetMyObjects` that takes a parameter `id` and returns a list of `MyObject` instances.

public List<MyObject> GetMyObjects(int id)
{
    var query = "SELECT * FROM MyTable WHERE Id = @Id";
    var parms = new Dictionary<string, object> { { "@Id", id } };
    return _connection.Query<MyObject>(query, parms);
}

In this example, we’re creating a query that selects all columns from `MyTable` where the `Id` column is equal to the `id` parameter. We’re then creating a dictionary of parameters, where the key is the parameter name (`@Id`) and the value is the parameter value (`id`).

Finally, we’re using the `Query` method of the `SQLiteConnection` instance to execute the query and return a list of `MyObject` instances.

Population of List of Objects

Now that we have our query results, let’s populate a list of objects with the data. We’ll create a new class called `MyObject` to represent our data.

public class MyObject
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }
}

In our `GetMyObjects` method, we’re using the `Query` method of the `SQLiteConnection` instance to execute the query and return a list of `MyObject` instances. The `Query` method will automatically map the query results to the properties of our `MyObject` class.

Example Usage

Let’s create an example usage of our `GetMyObjects` method. We’ll create a new page in our .NET Maui project called `MyPage`.

public partial class MyPage : ContentPage
{
    private readonly DatabaseService _databaseService;

    public MyPage()
    {
        InitializeComponent();
        _databaseService = new DatabaseService("mydatabase.db3");
    }

    private async void Button_Clicked(object sender, EventArgs e)
    {
        var myObjects = await Task.Run(() => _databaseService.GetMyObjects(1));
        MyListView.ItemsSource = myObjects;
    }
}

In this example, we’re creating a new page called `MyPage` that has a `Button` and a `ListView` called `MyListView`. When the button is clicked, we’re calling our `GetMyObjects` method and passing in the parameter `1`. We’re then setting the `ItemsSource` of our `ListView` to the list of `MyObject` instances returned by the `GetMyObjects` method.

Troubleshooting Common Issues

Error: SQLite query with parameters not working

If you’re having issues with your SQLite query not working with parameters, make sure you’re using the correct syntax for parameter names. In SQLite, parameter names should start with the `@` symbol.

Error: SQLite query returning null

If your SQLite query is returning null, make sure you’re checking for null before trying to access the results. You can do this by using the null-conditional operator (`?.`) in C#.

var myObjects = await Task.Run(() => _databaseService.GetMyObjects(1));
MyListView.ItemsSource = myObjects?.ToList();

Conclusion

Running a SQLite query with parameters and populating a list of objects in .NET Maui is a straightforward process. By following the steps outlined in this guide, you should be able to create a robust and efficient database-driven application.

Additional Resources

• Xamarin.Forms Database Documentation
• SQLite Documentation

Tip	Description
Use parameterized queries to prevent SQL injection.	Parameterized queries help prevent SQL injection by separating the SQL code from the data.
Use transactions to improve performance.	Transactions can improve performance by reducing the number of database operations.

By following the tips and best practices outlined in this guide, you’ll be well on your way to creating a robust and efficient database-driven application in .NET Maui. Happy coding!

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