---
title: Common Column Types
---

One of the key design goals of Cratis Arc support for Entity Framework is to make it easy to support
different databases for an application.

If you're willing to hand-roll Entity Framework migrations, you can leverage the extension methods that will give you
a single migration but support different database types resolved at runtime.

## Available Column Extension Methods

The following table shows all the column extension methods available in Cratis Arc:

| Extension Method | Description | Supported Types | Parameters |
|------------------|-------------|-----------------|------------|
| `StringColumn()` | Creates a string column with appropriate database-specific type (VARCHAR/NVARCHAR/TEXT) | string | `maxLength` (int?, optional), `nullable` (bool, default: true) |
| `NumberColumn<T>()` | Creates a numeric column with appropriate database-specific type for any numeric type | char, byte, sbyte, short, ushort, int, uint, long, ulong, float, double, decimal | `nullable` (bool, default: true) |
| `BoolColumn()` | Creates a boolean column with appropriate database-specific type (BOOLEAN/BIT/INTEGER) | bool | `nullable` (bool, default: true) |
| `AutoIncrementColumn()` | Creates an auto-incrementing integer column with appropriate database-specific annotations | int | None (always non-nullable) |
| `GuidColumn()` | Creates a GUID/UUID column with appropriate database-specific type (UUID/UNIQUEIDENTIFIER/TEXT) | Guid | `nullable` (bool, default: true) |
| `DateTimeOffsetColumn()` | Creates a DateTimeOffset column with appropriate database-specific type (TIMESTAMPTZ/DATETIMEOFFSET/TEXT) | DateTimeOffset | `nullable` (bool, default: true) |
| `JsonColumn<T>()` | Creates a JSON column with appropriate database-specific type (jsonb/nvarchar(max)/text) | Any type | None (always non-nullable) |

## Database-Specific Type Mappings

The extension methods automatically select the appropriate SQL type based on the database provider:

### String Types

- **PostgreSQL**: `VARCHAR(n)` for limited length, `TEXT` for unlimited
- **SQL Server**: `NVARCHAR(n)` for limited length, `NVARCHAR(MAX)` for unlimited  
- **SQLite**: `TEXT`

### Numeric Types

The `NumberColumn<T>()` method supports all .NET numeric types and maps them appropriately:

- **PostgreSQL**: SMALLINT, INTEGER, BIGINT, NUMERIC, REAL, DOUBLE PRECISION, DECIMAL
- **SQL Server**: TINYINT, SMALLINT, INT, BIGINT, DECIMAL, REAL, FLOAT
- **SQLite**: INTEGER, REAL (simplified type system)

### Boolean Types

- **PostgreSQL**: `BOOLEAN`
- **SQL Server**: `BIT`
- **SQLite**: `INTEGER`

### GUID/UUID Types

- **PostgreSQL**: `UUID`
- **SQL Server**: `UNIQUEIDENTIFIER`
- **SQLite**: `TEXT`

### DateTime Types

- **PostgreSQL**: `TIMESTAMPTZ`
- **SQL Server**: `DATETIMEOFFSET`
- **SQLite**: `TEXT`

### JSON Types

- **PostgreSQL**: `jsonb`
- **SQL Server**: `nvarchar(max)`
- **SQLite**: `text`

> Note: Read more about JSON in [this article](/arc/backend/entity-framework/json/)

## Usage Examples

### Auto Incremental Primary Key

Auto incremental primary keys are very common but implemented in different ways with different annotations for them to
actual auto increment. The `.AutoIncrementColumn()` extension method for the `ColumnsBuilder` gives you a way to configure
it once.

```csharp
[DbContext(typeof(EventLogDbContext))]
[Migration($"EventLog_{nameof(v1_0_0)}")]
public class v1_0_0 : Migration
{
    protected override void Up(MigrationBuilder migrationBuilder)
    {
        migrationBuilder.CreateTable(
            name: "EventLog",
            columns: table => new
            {
                SequenceNumber = table.AutoIncrementColumn(migrationBuilder), // Creates an auto increment column
                /*
                Other columns...
                */
            },
            constraints: table => table.PrimaryKey("PK_EventLog", x => x.SequenceNumber));
    }
}
```

### String Columns with Length Limits

```csharp
columns: table => new
{
    Name = table.StringColumn(migrationBuilder, maxLength: 100), // VARCHAR(100)/NVARCHAR(100)
    Description = table.StringColumn(migrationBuilder), // TEXT/NVARCHAR(MAX)
}
```

### Numeric Columns

```csharp
columns: table => new
{
    Count = table.NumberColumn<int>(migrationBuilder), // INTEGER/INT
    Price = table.NumberColumn<decimal>(migrationBuilder), // DECIMAL
    Score = table.NumberColumn<double>(migrationBuilder), // DOUBLE PRECISION/FLOAT/REAL
}
```

### Other Column Types

```csharp
columns: table => new
{
    IsActive = table.BoolColumn(migrationBuilder), // BOOLEAN/BIT/INTEGER
    Id = table.GuidColumn(migrationBuilder, nullable: false), // UUID/UNIQUEIDENTIFIER/TEXT
    CreatedAt = table.DateTimeOffsetColumn(migrationBuilder), // TIMESTAMPTZ/DATETIMEOFFSET/TEXT
    Metadata = table.JsonColumn<Dictionary<string, object>>(migrationBuilder), // jsonb/nvarchar(max)/text
}
```