---
title: "Type Converters"
description: "Convert between C# types and database types with custom converters."
canonical: "https://roomsharp.dev/docs/v0.5.3/type-converters"
source: "src/content/v0.5.3/type-converters.mdx"
---

# Type Converters

Type converters allow you to map complex C# types to database-compatible types and vice versa.

## Creating a Type Converter

Implement `ITypeConverter<TProvider, TModel>` or derive from `TypeConverter<TProvider, TModel>`:

```csharp
public class DateTimeTicksConverter : TypeConverter<long, DateTime>
{
    public override DateTime FromProvider(long provider) 
        => new(provider, DateTimeKind.Utc);
    
    public override long ToProvider(DateTime model) 
        => model.ToUniversalTime().Ticks;
}
```

## Applying Type Converters

Annotate entity properties with `[TypeConverter(ConverterType = typeof(...))]`:

```csharp
[Entity(TableName = "posts")]
public class Post
{
    [PrimaryKey(AutoGenerate = true)] 
    public long Id { get; set; }

    [TypeConverter(ConverterType = typeof(DateTimeTicksConverter))]
    public DateTime PublishedAt { get; set; }
}
```

## Generic Type Converter Attribute

For simpler syntax, use the generic attribute (C# 11+):

```csharp
[Entity(TableName = "users")]
public class User
{
    [PrimaryKey(AutoGenerate = true)]
    public long Id { get; set; }
    
    [TypeConverter<EnumToStringConverter<UserStatus>>]
    public UserStatus Status { get; set; }
    
    [TypeConverter<JsonConverter<UserSettings>>]
    public UserSettings? Settings { get; set; }
}
```

## Common Converters

### Enum to String

```csharp
public class EnumToStringConverter<TEnum> : TypeConverter<string, TEnum>
    where TEnum : struct, Enum
{
    public override TEnum FromProvider(string provider) 
        => Enum.Parse<TEnum>(provider);
    
    public override string ToProvider(TEnum model) 
        => model.ToString();
}
```

### JSON Serialization

```csharp
public class JsonConverter<T> : TypeConverter<string, T>
{
    public override T FromProvider(string provider) 
        => JsonSerializer.Deserialize<T>(provider)!;
    
    public override string ToProvider(T model) 
        => JsonSerializer.Serialize(model);
}
```

### DateTime to Ticks

```csharp
public class DateTimeTicksConverter : TypeConverter<long, DateTime>
{
    public override DateTime FromProvider(long provider) 
        => new(provider, DateTimeKind.Utc);
    
    public override long ToProvider(DateTime model) 
        => model.ToUniversalTime().Ticks;
}
```

### Guid to String

```csharp
public class GuidStringConverter : TypeConverter<string, Guid>
{
    public override Guid FromProvider(string provider) 
        => Guid.Parse(provider);
    
    public override string ToProvider(Guid model) 
        => model.ToString("D");
}
```

## Registering Converters at Runtime

RoomSharp discovers converters on entities automatically, but you can also register them at runtime:

```csharp
var db = RoomDatabase.Builder<AppDatabaseImpl>()
    .UseSqlite("app.db")
    .Build();

// Register custom converter
db.Converters.Register(new MyCustomConverter());
```

<Tip>
Converters discovered on entities are automatically registered. Use runtime registration for converters that apply to multiple entities or when you need dynamic behavior.
</Tip>

## Nullable Type Handling

For nullable types, handle null values appropriately:

```csharp
public class NullableDateTimeTicksConverter : TypeConverter<long?, DateTime?>
{
    public override DateTime? FromProvider(long? provider) 
        => provider.HasValue ? new DateTime(provider.Value, DateTimeKind.Utc) : null;
    
    public override long? ToProvider(DateTime? model) 
        => model?.ToUniversalTime().Ticks;
}
```

## Type Mapping Reference

Default type mappings without converters:

| C# Type | SQLite Type | Notes |
|---------|-------------|-------|
| `int`, `long`, `short` | INTEGER | Numeric types |
| `string` | TEXT | Text data |
| `double`, `float`, `decimal` | REAL | Floating point |
| `byte[]` | BLOB | Binary data |
| `DateTime` | INTEGER | Stored as Unix ticks |
| `bool` | INTEGER | 0 or 1 |
| `Guid` | TEXT | String representation |

<Note>
Use type converters when you need different storage formats or want to serialize complex objects to JSON/string.
</Note>