C#•3w ago

Resolving Entity Framework Core Tracking Issues with Shared Relationships in .NET MAUI and SQLite

Context: I am developing a .NET MAUI application using Entity Framework Core with SQLite as the local database provider. The application involves managing workouts, exercises, and exercise variants. Below is a detailed explanation of my workflow and the issue I am encountering: Workflow Saving Default Exercise Variants Locally Upon user login, I fetch a predefined list of exercise variants (with fixed IDs) and save them locally using the following code:

await _dbContext.AddRangeAsync(exerciseVariants, cancellationToken);
await _dbContext.SaveChangesAsync().ConfigureAwait(false);

await _dbContext.AddRangeAsync(exerciseVariants, cancellationToken);
await _dbContext.SaveChangesAsync().ConfigureAwait(false);

Retrieving All Exercise Variants To retrieve all locally stored exercise variants, I use the following query:

var allExerciseVariants = await dbContext.ExerciseVariant
    .AsNoTracking()
    .ToListAsync(cancellationToken);

var allExerciseVariants = await dbContext.ExerciseVariant
    .AsNoTracking()
    .ToListAsync(cancellationToken);

Creating and Saving a Workout When creating a workout, I define it with associated exercises as shown below:

var workout = new Workout()
{
    Title = "Test"
};

var exercises = new List<Exercise>()
{
    new Exercise()
    {
        Note = "Test note",
        ExerciseVariant = allExerciseVariants.FirstOrDefault(), // Selecting the first variant for testing purposes
    }
};

workout.Exercises.AddRange(exercises);

await dbContext.Workout.AddAsync(workout);
await dbContext.SaveChangesAsync();

var workout = new Workout()
{
    Title = "Test"
};

var exercises = new List<Exercise>()
{
    new Exercise()
    {
        Note = "Test note",
        ExerciseVariant = allExerciseVariants.FirstOrDefault(), // Selecting the first variant for testing purposes
    }
};

workout.Exercises.AddRange(exercises);

await dbContext.Workout.AddAsync(workout);
await dbContext.SaveChangesAsync();

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4 Replies

ZoliOP•3w ago

Entity Structure: Here is the class structure for my entities and their relationships:

public class Workout
{
    [Key]
    public Guid Id { get; set; }

    public required string Title { get; set; }

    public string? Note { get; set; }

    public ICollection<Exercise> Exercises { get; } = new List<Exercise>();
}

public class Exercise
{
    [Key]
    public Guid Id { get; set; }

    public Guid? ExerciseVariantId { get; set; }
    public ExerciseVariant ExerciseVariant { get; set; }

    public string? Note { get; set; }

    // Foreign keys
    public Guid? WorkoutId { get; set; }
    public Workout? Workout { get; set; }
}

public class ExerciseVariant
{
    [Key]
    public Guid Id { get; set; }
    
    public string Name { get; set; }

    public BodyPart BodyPart { get; set; }

    public Category Category { get; set; }

    public string? Video { get; set; }

    public bool IsCustom { get; set; }

    public ICollection<Exercise> Exercises { get; } = new List<Exercise>();
}

public class Workout
{
    [Key]
    public Guid Id { get; set; }

    public required string Title { get; set; }

    public string? Note { get; set; }

    public ICollection<Exercise> Exercises { get; } = new List<Exercise>();
}

public class Exercise
{
    [Key]
    public Guid Id { get; set; }

    public Guid? ExerciseVariantId { get; set; }
    public ExerciseVariant ExerciseVariant { get; set; }

    public string? Note { get; set; }

    // Foreign keys
    public Guid? WorkoutId { get; set; }
    public Workout? Workout { get; set; }
}

public class ExerciseVariant
{
    [Key]
    public Guid Id { get; set; }
    
    public string Name { get; set; }

    public BodyPart BodyPart { get; set; }

    public Category Category { get; set; }

    public string? Video { get; set; }

    public bool IsCustom { get; set; }

    public ICollection<Exercise> Exercises { get; } = new List<Exercise>();
}

Data Context Configuration:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    // Configure Exercise -> ExerciseVariant relationship
    modelBuilder.Entity<Exercise>()
        .HasOne(e => e.ExerciseVariant)
        .WithMany(ev => ev.Exercises)
        .HasForeignKey(e => e.ExerciseVariantId);

    // Configure Workout -> Exercise relationship
    modelBuilder.Entity<Workout>()
        .HasMany(w => w.Exercises)
        .WithOne(e => e.Workout)
        .HasForeignKey(e => e.WorkoutId)
        .OnDelete(DeleteBehavior.Cascade);

    base.OnModelCreating(modelBuilder);
}

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    // Configure Exercise -> ExerciseVariant relationship
    modelBuilder.Entity<Exercise>()
        .HasOne(e => e.ExerciseVariant)
        .WithMany(ev => ev.Exercises)
        .HasForeignKey(e => e.ExerciseVariantId);

    // Configure Workout -> Exercise relationship
    modelBuilder.Entity<Workout>()
        .HasMany(w => w.Exercises)
        .WithOne(e => e.Workout)
        .HasForeignKey(e => e.WorkoutId)
        .OnDelete(DeleteBehavior.Cascade);

    base.OnModelCreating(modelBuilder);
}

The Issue: When I attempt to create a workout and associate it with an existing ExerciseVariant, I encounter the following error: The instance of entity type 'ExerciseVariant' cannot be tracked because another instance with the same key value for {'Id'} is already being tracked. I have already tried using AsNoTracking when retrieving the ExerciseVariant, but the issue persists. How can i solve this issue? Is there a recommended way to handle such scenarios where an entity with shared relationships needs to be reused?

Sehra•3w ago

it's likely being tracked from await _dbContext.AddRangeAsync(exerciseVariants, cancellationToken);, you can clear it with _dbContext.ChangeTracker.Clear() or detach entities individually. keep in mind DbContext is supposed to be short lived

ZoliOP•3w ago

Shall I call _dbContext.ChangeTracker.Clear() after each await dbContext.SaveChangesAsync();?

Joschi•3w ago

Not really. Most of the time your dbcontext should not outlive a SaveChanges call. One dbContext should more or less be used for one unit of work.

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Resolving Entity Framework Core Tracking Issues with Shared Relationships in .NET MAUI and SQLite

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