【高级技巧】版本对齐读：多表联查的一致性保证

local aligned = {
    current = { item = nil, drop = nil, shop = nil },
    snapshot = { item = nil, drop = nil, shop = nil },
}
local function tryAlign()
    local c = aligned.current
    if c.item.version == c.drop.version and c.item.version == c.shop.version then
        aligned.snapshot = c
        return true
    end
    return false
end
local function readAligned()
    if not tryAlign() then
        return aligned.snapshot
    end
    return aligned.current
end

local function queryShopPrice(itemId)
    local v = readAligned()
    local base = v.item[itemId].price
    local factor = v.shop.rate
    return math.floor(base * factor)
end