.Net: Bug: [SqliteVectorStore] NOT NULL constraint failed: words.json during UpsertAsync

[P47K0]

Describe the bug
Calling UpsertAsync (single or batch) on a SqliteVectorStore collection throws:

SQLite Error 19: 'NOT NULL constraint failed: words.json'

The json column in the words table (or collection-named table) is defined as NOT NULL, but the connector serializes the non-vector properties into a null or empty value, violating the constraint.

Even after:

• GetCollection succeeds
• Dummy upsert attempts (single record, non-zero vector, empty batch) fail with the same error

To Reproduce

[VectorStoreRecord]
public record HangmanWordRecord
{
    [VectorStoreRecordKey]
    public int Key { get; init; }

    [VectorStoreData]
    public string Word { get; init; } = string.Empty;

    [VectorStoreData]
    public string Category { get; init; } = string.Empty;

    [VectorStoreData]
    public string Language { get; init; } = string.Empty;

    [VectorStoreData]
    public int Length { get; init; }

    [VectorStoreRecordVector(Dimensions = 768)]
    public ReadOnlyMemory<float> Embedding { get; init; } = default;
}

var store = new SqliteVectorStore("Data Source=:memory:");
var collection = store.GetCollection<int, HangmanWordRecord>("words");

var record = new HangmanWordRecord
{
    Key = 1,
    Word = "apple",
    Category = "food",
    Language = "en",
    Length = 5,
    Embedding = new ReadOnlyMemory<float>(new float[768])
};

await collection.UpsertAsync(record);  // throws NOT NULL constraint failed: words.json

Expected behavior

• UpsertAsync succeeds
• json column contains serialized non-vector properties (or is nullable if empty)

Workarounds tried

• Explicit non-empty string values in all [VectorStoreData] properties — still fails
• Relaxed schema (json TEXT without NOT NULL) — insert succeeds, but json column remains null/empty
• Manual raw SQL insert with JsonSerializer.Serialize — works reliably

Screenshots

Platform

• Language: C#
• .NET: 10.0
• Source:
  • Semantic Kernel version: 1.70.0
  • Connector: Microsoft.SemanticKernel.Connectors.SqliteVec 1.70.0-preview
• Database: SQLite (file-based)
• vec0.dll ->0.1.7-alpha.2 (loadable extension from https://github.com/asg017/sqlite-vec/releases)
• AI model: nomic-embed-text via ollama
• IDE: Visual Studio 2026 Pro
• OS: Winsows 11 x64
• GPU: Intel Arc iGPU

Additional context

• Occurs with both in-memory SQLite file-based DB
• Same issue in SqliteVec connector (chunk tables also remain empty)
• Manual SQL workaround bypasses the bug completely

You can see my simple Hangman game where I encountered the issue here:
https://github.com/P47K0/SKOrchestrationPractice