sync-function.js

// Sync Gateway Sync Function skeleton
// Assigned to an App Endpoint (Sync Gateway database config)
// Called for every document write — controls access, routing, and validation.

function sync(doc, oldDoc) {
    // --- Validation ---
    if (!doc.type) {
        throw({ forbidden: "Document must have a 'type' field" });
    }

    // Prevent changing document type
    if (oldDoc && oldDoc.type !== doc.type) {
        throw({ forbidden: "Cannot change document type" });
    }

    // --- Channel routing ---
    // Route to a user-specific channel
    if (doc.userId) {
        channel("user." + doc.userId);
    }

    // Route to a shared channel by type
    channel(doc.type);

    // --- Access control ---
    // Grant the owning user read/write access to their channel
    if (doc.userId) {
        access(doc.userId, "user." + doc.userId);
    }

    // Grant admins access to all channels
    access("role:admin", "*");

    // --- Role assignment ---
    // Assign roles based on document content
    if (doc.type === "user" && doc.role) {
        role(doc.userId, "role:" + doc.role);
    }
}