# Model the schema

Define the projects and tasks tables as annotated C# classes. Attributes map them to PostgreSQL columns, defaults, keys, and a foreign-key relationship.

In `Socigy.OpenSource.DB` the C# class **is** the schema. Each `[Table]` class is a partial class so the generator can add the typed query methods to it at build time.

## The project table

```csharp
// TaskApi.AppDb/Project.cs
using Socigy.OpenSource.DB.Attributes;

[Table("projects")]
public partial class Project
{
    [PrimaryKey, Default(DbDefaults.Guid.Random)]
    public Guid Id { get; set; }

    [Unique]
    public required string Name { get; set; }

    [Default(DbDefaults.Time.Now)]
    public DateTime CreatedAt { get; set; }
}
```

- `[Table("projects")]` sets the SQL table name. The class must be `partial`.
- `[PrimaryKey, Default(DbDefaults.Guid.Random)]` makes `Id` the primary key and tells the database to generate a random UUID, so callers never set it.
- `[Unique]` adds a unique constraint on `name`.
- `[Default(DbDefaults.Time.Now)]` stamps `created_at` server-side.

Property names map to `snake_case` columns automatically: `CreatedAt` becomes `created_at`. All of these attributes live in `Socigy.OpenSource.DB.Attributes`.

## The task table

```csharp
// TaskApi.AppDb/TaskItem.cs
using Socigy.OpenSource.DB.Attributes;

[Table("tasks")]
public partial class TaskItem
{
    [PrimaryKey, Default(DbDefaults.Guid.Random)]
    public Guid Id { get; set; }

    [ForeignKey(typeof(Project), OnDelete = DbValues.ForeignKey.Cascade)]
    public Guid ProjectId { get; set; }

    public required string Title { get; set; }

    public bool Done { get; set; }

    [Default(DbDefaults.Time.Now)]
    public DateTime CreatedAt { get; set; }
}
```

`[ForeignKey(typeof(Project), ...)]` on `ProjectId` references `Project`'s primary key automatically. `OnDelete = DbValues.ForeignKey.Cascade` deletes a project's tasks when the project is removed. See [Constraints](/database/0.3.2/defining-models/constraints) for composite keys and other referential actions.

> **NOTE** Nothing here is reflection or runtime configuration. The generator reads these attributes at compile time and emits plain C#. See [How it works](/database/0.3.2/core-concepts/how-it-works).

With the schema modelled, the next step turns it into a real database. Continue to [Generate and apply migrations](/database/0.3.2/tutorial/migrations).