请问是需要通过事件跟踪struct还是需要自己在the graph里额外编写，struct如下，要获取结构体中buyprice的最大值，也定义了相应事件:

struct tradeMes {
        uint64 tradeId;
        uint64 buyTime;
        uint128 buyTotalAmount; 
        uint128 buyPrice; 
        uint128 tradeState; 
        address tokenAddress;
        address buyerAddress;
        address solderAddress;
    }
    tradeMes[] private  _tradeMes;

    //事件
    event tradeMessage(uint64 id,uint64 buyTime,uint128 amount,uint128 price,uint128 tradeState,address choosedToken,address buyerAddress,address solderAddress);