Sylin.Koan.Data.Connector.Json

Sylin.Koan.Data.Connector.Json

Persist ordinary Koan Entities in inspectable local JSON files without running a database server.

Use it

dotnet add package Sylin.Koan.Data.Connector.Json

Keep the normal Koan bootstrap and Entity API:

builder.Services.AddKoan();

public sealed class Todo : Entity<Todo>
{
    public string Title { get; set; } = "";
}

var saved = await new Todo { Title = "Ship" }.Save(ct);
var same = await Todo.Get(saved.Id, ct);

The managed default directory is data. Choose another root only when placement matters:

{
  "Koan": {
    "Data": {
      "Json": { "DirectoryPath": "state" }
    }
  }
}

Named sources use the standard source grammar and may choose their own json:DirectoryPath.

What succeeds

• Managed/read-write use creates the directory and Entity file on the first write.
• Every read returns a detached Entity. Editing it changes nothing until Save() succeeds.
• A write builds a complete candidate file, replaces the target, then publishes the new live snapshot.
• Bulk upsert and delete each perform one physical file replacement.
• A new Koan host restores root/variant identity and managed isolation fields from disk.
• Two source path spellings that resolve to the same canonical file share one in-process snapshot and write gate.

Boundaries and failures

• Corrupt JSON, duplicate identities, incompatible Entity roots, and files larger than 64 MiB never become an empty successful store.
• Read-only writes fail before filesystem mutation.
• External requires an existing directory and Entity file; Koan never provisions either.
• Physical Map<T> declarations reject because the connector owns one Entity-array file shape.
• Required atomic batches and provider-bounded Entity streams reject before partial work.
• The 1,025th canonical Entity/partition file in one host rejects; the fixed 1,024-file ceiling keeps host state finite.

Choose a database connector when

You need multi-process writers, transactions, indexes, provider-side queries, crash-recovery guarantees, files above 64 MiB, or dynamically unbounded partitions. JSON is a deliberately small local persistence floor. It does not watch for external edits after a file enters the host cache, and lexical path canonicalization does not promise to collapse every symlink alias.

Use FirstPage/Page to limit results returned to application code. AllStream and QueryStream remain unavailable because loading a whole file before yielding would not be provider-bounded streaming.

See TECHNICAL.md for the exact storage and capability contract.