FDDB121: Prefix not applicable to constant key

Field	Value
Code	FDDB121
Severity	Error

Message

Property '{0}' is a constant key but has Prefix configured — prefix is meaningless on a constant value

Description

A key property detected as a constant key (via expression-body or read-only auto-property syntax) cannot have a Prefix configured on [PartitionKey] or [SortKey]. The constant value already contains the exact key value that will be stored in DynamoDB — there is no variable portion to prepend a prefix to.

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(Prefix = "USER")]
    [DynamoDbAttribute("pk")]
    public string Pk => "CONSTANT_VALUE";  // Constant + Prefix = conflict
}

Fix

Remove the Prefix — the constant value already IS the full key value:

[DynamoDbTable("customers")]
public partial class Customer
{
    [PartitionKey]
    [DynamoDbAttribute("pk")]
    public string Pk => "USER#CONSTANT_VALUE";  // Include prefix in the constant itself
}

Or, if the key needs a prefix with a variable part, don't use a constant key:

[DynamoDbTable("customers")]
public partial class Customer
{
    [PartitionKey(Prefix = "USER")]
    [DynamoDbAttribute("pk")]
    public string Pk { get; set; } = string.Empty;  // Variable key with prefix
}