FDDB122: Cannot extract from constant key

Field	Value
Code	FDDB122
Severity	Error

Message

Property '{0}' has [Extracted] referencing constant key property '{1}' — extraction from a constant is invalid

Description

An [Extracted] attribute references a key property that has been detected as a constant key. Extraction splits a composite key into component parts, but a constant key has a fixed value with no variable components to extract.

When this diagnostic fires, code generation is halted for the affected entity.

Example

The following code triggers this diagnostic:

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

    [SortKey]
    [DynamoDbAttribute("sk")]
    public string Sk => "PROFILE";  // Constant key

    [Extracted("Sk", 0)]
    [DynamoDbAttribute("skPart")]
    public string SkPart { get; set; } = string.Empty;  // Can't extract from constant
}

Fix

Remove the [Extracted] attribute — there are no variable components in a constant key to extract:

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

    [SortKey]
    [DynamoDbAttribute("sk")]
    public string Sk => "PROFILE";

    // If you need the constant value elsewhere, reference it directly
    // or use a regular property
}