Very easy sync code logic.

Sync.swift

var server_data = [0, 11, 13, 15]
var local_data = [1, 11, 12]

for (i, local) in server_data.enumerated() {
    for (j, server) in local_data.enumerated() {
        if local.id == server.id {
            server_data.remove(at: i)
            local_data.remove(at: j)
            // Update record.
            // Write a code to update a record in the coredata
        }
    }
}

for (i, server) in server_data.enumerated() {
    server_data.remove(at: i)
    // Insert record
    // Write a code to insert a record in the coredata
}

for (i, local) in local_data.enumerated() {
    local_data.remove(at: i)
    // Delete the record
    // Write a code to delete a record from the coredata
}