PROJ004: Projection must be partial

Field	Value
Code	PROJ004
Severity	Error

Message

Projection class '{0}' must be declared as 'partial' to support source generation

Description

Projection classes must be declared as partial to allow the source generator to add mapping code. The source generator extends the projection class with implementations of IReadOnlyEntity and IProjectionModel, which requires the class to be declared with the partial keyword.

Without the partial modifier, the source generator cannot add the generated code to the class, and the projection will not function correctly at runtime.

Example

The following code triggers this diagnostic:

[DynamoDbTable("Orders")]
public partial class Order
{
    [PartitionKey]
    [DynamoDbAttribute("pk")]
    public string Pk { get; set; } = string.Empty;

    [DynamoDbAttribute("status")]
    public string Status { get; set; } = string.Empty;
}

// PROJ004: class must be declared as 'partial'
[DynamoDbProjection(typeof(Order))]
public class OrderSummary
{
    [DynamoDbAttribute("status")]
    public string Status { get; set; } = string.Empty;
}

Fix

The corrected version:

[DynamoDbTable("Orders")]
public partial class Order
{
    [PartitionKey]
    [DynamoDbAttribute("pk")]
    public string Pk { get; set; } = string.Empty;

    [DynamoDbAttribute("status")]
    public string Status { get; set; } = string.Empty;
}

[DynamoDbProjection(typeof(Order))]
public partial class OrderSummary
{
    [DynamoDbAttribute("status")]
    public string Status { get; set; } = string.Empty;
}