NeuroAgent

Fix EF Core SQLite DateOnly Query Error: 'N' Invalid Start Value

Learn how to fix EF Core SQLite query error: 'N' is an invalid start of value. Discover solutions for DateOnly type handling issues, proper value converters, and database configuration. Complete guide with code examples.

#database-query#dateonly-error#dotnet-maui#ef-core#entity-framework#json-parsing#sqlite
Question

How to Fix EF Core SQLite Query Error: ‘N’ is an Invalid Start of a Value

I’m encountering an error when querying SQLite with Entity Framework Core in my .NET 9 Maui application. The error message is:

'N' is an invalid start of a value. LineNumber: 0 | BytePositionInLine: 0.

This exception is being thrown from:

  • System.Text.Json.JsonReaderException in System.Text.Json.dll
  • System.Text.Json.JsonReaderException in Microsoft.EntityFrameworkCore.Relational.dll

My Repository Method

csharp
public void GetMoviesAsync()
{
    try
    {
        using (var movieContext = new MovieContext())
        {
            var movies = movieContext.Movies
                     .AsNoTracking()
                     .ToList<Movie>();

            //return movies ?? new List<Movie>();
        }
    }
    catch (Exception ex)
    {
        throw new Exception(ex.Message);
    }
}

Additional Information

When I tried running the query as raw SQL:

csharp
movieContext.Database.ExecuteSqlRaw("Select * From Movies");

It returned -1, indicating no rows were returned.

Movie Class Definition

csharp
public class Movie
{
    [Key]
    public int MovieId { get; set; }

    [Required]
    public string Title { get; set; }

    public DateOnly ReleaseDate { get; set; }
    public string Genre { get; set; }
    public string[] Tags { get; set; }

    public string MovieLocation { get; set; }
    public string ImageLocation { get; set; }

    public int GroupId { get; set; }
}

Data Context Configuration

csharp
public class MovieContext : DbContext
{
    public DbSet<Movie> Movies { get; set; }
    public DbSet<Group> Groups { get; set; }

    public MovieContext()
    {
        SQLitePCL.Batteries_V2.Init();
        this.Database.EnsureCreated();
    }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) =>
           optionsBuilder.UseSqlite("Data Source = D:\\Repos\\MovieManager\\MovieManager.db3");
}

Database Data

The database contains one row of data, but I’m unable to retrieve it due to the error. The error seems to suggest there’s an issue with JSON parsing, possibly related to the character “N” in the data.

What I’ve Tried

  1. Using AsNoTracking() for better performance
  2. Attempting raw SQL query
  3. Verifying database connection and data existence

Question

What could be causing this EF Core SQLite query error, and how can I resolve it? Is there an issue with the data in my database, or is there a configuration problem with my EF Core setup?

NeuroAgent

The error “‘N’ is an invalid start of a value” in EF Core with SQLite typically occurs when there’s a mismatch between how data is stored in the database and how EF Core attempts to deserialize it, particularly with the DateOnly type. This specific error indicates that System.Text.Json is encountering an unexpected character “N” when trying to parse the database response, which commonly happens with improperly stored DateOnly values.

Contents

Understanding the Root Cause

The error occurs because EF Core’s SQLite provider attempts to deserialize database values into your entity types, but encounters unexpected data format. The “N” character specifically suggests that a null or empty value is being stored where a valid date should exist.

Based on the research, this is particularly common with DateOnly types when:

  • The database column contains null values stored as “NULL” string
  • DateOnly values are stored in an unexpected format
  • There’s a mismatch between how data was initially inserted and how EF Core expects it to be read

As noted in the Stack Overflow discussion, users with identical DateOnly configurations have encountered the same parsing issue when querying SQLite databases.

DateOnly Type Configuration Issues

The DateOnly type in EF Core with SQLite requires special configuration because:

  1. Native Support: While SQLite provider supports DateOnly, it needs proper value conversion
  2. Storage Format: By default, EF Core may store DateOnly as string values rather than native date types
  3. Null Handling: Null DateOnly values can cause parsing errors if not properly configured

According to the Microsoft EF Core 8 documentation, DateOnly types are handled differently across database providers, and SQLite requires specific configuration to avoid serialization issues.

Database Data Validation

Since your raw SQL query returned -1 (no rows affected), but you mentioned there’s data in the database, let’s verify the actual data format:

csharp
// Direct database inspection to check data format
public void InspectDatabaseData()
{
    using (var connection = new SqliteConnection("Data Source = D:\\Repos\\MovieManager\\MovieManager.db3"))
    {
        connection.Open();
        using (var command = connection.CreateCommand())
        {
            command.CommandText = "SELECT MovieId, Title, ReleaseDate FROM Movies";
            using (var reader = command.ExecuteReader())
            {
                while (reader.Read())
                {
                    Console.WriteLine($"MovieId: {reader.GetInt32(0)}");
                    Console.WriteLine($"Title: {reader.GetString(1)}");
                    Console.WriteLine($"ReleaseDate: {reader.GetValue(2)} (Type: {reader.GetFieldType(2)})");
                }
            }
        }
    }
}

Common issues to look for:

  • ReleaseDate column contains “NULL” instead of actual null values
  • Date values are stored as strings with unexpected formatting
  • Character encoding issues in the database file

EF Core Configuration Solutions

Solution 1: Configure DateOnly Value Converter

Add a value converter to handle DateOnly types properly:

csharp
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Movie>()
        .Property(m => m.ReleaseDate)
        .HasConversion(
            v => v.ToDateTime(TimeOnly.MinValue),  // Convert DateOnly to DateTime for storage
            v => DateOnly.FromDateTime(v)          // Convert DateTime back to DateOnly
        );
}

Solution 2: Use Proper SQLite Date Functions

Configure your context to use SQLite date functions:

csharp
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Movie>()
        .Property(m => m.ReleaseDate)
        .HasColumnType("TEXT");  // Explicitly specify column type
}

Solution 3: Enable JSON Support

Ensure JSON support is properly configured for SQLite:

csharp
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
    optionsBuilder.UseSqlite("Data Source = D:\\Repos\\MovieManager\\MovieManager.db3");
    
    // Add JSON-specific configuration if needed
    if (!optionsBuilder.IsConfigured)
    {
        optionsBuilder.UseSnakeCaseNamingConvention();
    }
}

Complete Fix Implementation

Here’s a complete implementation that addresses the DateOnly issue:

csharp
public class MovieContext : DbContext
{
    public DbSet<Movie> Movies { get; set; }
    public DbSet<Group> Groups { get; set; }

    public MovieContext()
    {
        SQLitePCL.Batteries_V2.Init();
        this.Database.EnsureCreated();
    }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) =>
        optionsBuilder.UseSqlite("Data Source = D:\\Repos\\MovieManager\\MovieManager.db3");

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        // Configure DateOnly property with proper conversion
        modelBuilder.Entity<Movie>()
            .Property(m => m.ReleaseDate)
            .HasConversion(
                v => v.ToDateTime(TimeOnly.MinValue),
                v => DateOnly.FromDateTime(v)
            )
            .HasColumnType("TEXT");
            
        // Configure Tags array if needed
        modelBuilder.Entity<Movie>()
            .Property(m => m.Tags)
            .HasConversion(
                v => JsonSerializer.Serialize(v, (JsonSerializerOptions)null),
                v => JsonSerializer.Deserialize<string[]>(v, (JsonSerializerOptions)null) ?? Array.Empty<string>()
            )
            .HasColumnType("TEXT");
    }
}

// Updated repository method with error handling
public async Task<List<Movie>> GetMoviesAsync()
{
    try
    {
        using (var movieContext = new MovieContext())
        {
            var movies = await movieContext.Movies
                .AsNoTracking()
                .ToListAsync();

            return movies ?? new List<Movie>();
        }
    }
    catch (Exception ex)
    {
        // Log the specific error for debugging
        Console.WriteLine($"Error retrieving movies: {ex.Message}");
        throw new Exception("Failed to retrieve movies from database", ex);
    }
}

Prevention and Best Practices

1. Data Insertion Best Practices

When inserting data with DateOnly types, ensure proper null handling:

csharp
public async Task InsertMovieAsync(Movie movie)
{
    using (var context = new MovieContext())
    {
        // Handle null DateOnly properly
        if (movie.ReleaseDate == default)
        {
            movie.ReleaseDate = null; // or set to a default date
        }
        
        context.Movies.Add(movie);
        await context.SaveChangesAsync();
    }
}

2. Database Migration Setup

Use proper migrations to ensure correct column types:

csharp
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Movie>(entity =>
    {
        entity.HasKey(e => e.MovieId);
        entity.Property(e => e.ReleaseDate).HasColumnType("TEXT");
        entity.Property(e => e.Tags).HasColumnType("TEXT");
    });
}

3. Connection String Validation

Ensure your connection string is properly formatted:

csharp
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
    var connectionString = "Data Source = D:\\Repos\\MovieManager\\MovieManager.db3";
    
    // Validate connection string
    if (string.IsNullOrWhiteSpace(connectionString))
    {
        throw new InvalidOperationException("Database connection string is not configured");
    }
    
    optionsBuilder.UseSqlite(connectionString);
}

Alternative Approaches

Approach 1: Use DateTime Instead of DateOnly

If DateOnly continues to cause issues, consider using DateTime:

csharp
public class Movie
{
    // ... other properties
    
    [Column(TypeName = "Date")]
    public DateTime ReleaseDate { get; set; }
}

Approach 2: Raw SQL with Custom Mapping

For complex scenarios, use raw SQL with custom mapping:

csharp
public async Task<List<Movie>> GetMoviesWithRawSql()
{
    using (var context = new MovieContext())
    {
        var movies = await context.Movies
            .FromSqlRaw("SELECT * FROM Movies")
            .ToListAsync();
            
        return movies;
    }
}

Approach 3: Database Schema Correction

If the existing data is corrupted, you may need to correct the database schema:

sql
-- Manual SQL to fix the ReleaseDate column
ALTER TABLE Movies DROP COLUMN ReleaseDate;
ALTER TABLE Movies ADD COLUMN ReleaseDate TEXT;

-- Update existing data
UPDATE Movies SET ReleaseDate = NULL WHERE ReleaseDate IS NULL;

Conclusion

The “‘N’ is an invalid start of a value” error in EF Core SQLite is typically caused by improper DateOnly type handling or corrupted data. The key solutions include:

  1. Proper DateOnly Configuration: Use value converters to ensure correct serialization/deserialization
  2. Data Validation: Check your database for unexpected null values or formatting issues
  3. EF Core Configuration: Ensure proper column types and JSON handling
  4. Error Handling: Implement robust error handling to identify specific data issues

Start by implementing the DateOnly value converter in your OnModelCreating method, then validate your existing data format. If the issue persists, consider using DateTime instead or manually correcting your database schema. Always test with a clean database instance when encountering serialization issues with EF Core.

Sources

  1. How can I solve an EF Core error querying SQLite? - Stack Overflow
  2. What’s New in EF Core 8 | Microsoft Learn
  3. DateOnly and TimeOnly support with Entity Framework Core 6.0
  4. Support the new BCL DateOnly and TimeOnly structs for Sqlite · GitHub
  5. EF Core and DateOnly – moscardino.net
How to properly configure DateOnly type in EF Core SQLite?What are the best practices for handling DateOnly types in Entity Framework Core?How to troubleshoot EF Core SQLite connection issues?What causes System.Text.Json JsonReaderException in EF Core?How to migrate from DateTime to DateOnly in EF Core?What are the differences between EF Core SQLite and SQL Server date handling?
Ask NeuroAgent